Appendix 1 

Acronyms and Abbreviations 

APPENDIX 1 

ACRONYMS AND ABBREVIATIONS 

AAPG American Association of Petroleum Geologists 

AD Associated Dissolved (natural gas) 

APD Application for Permit to Drill 

ARMP Approved Resource Management Plan 

bbl Barrels (of oil) 

BLM Bureau of Land Management 

BOE Barrels of Oil Equivalent 

CBM Coal Bed Methane 

CEQ Council on Environmental Quality 

CFR Code of Federal Regulations 

CPAs Citizen's Proposal Areas 

CSU Control Surface Usage 

DEM Digital Elevation Model 

DOE Department of Energy 

DOI Department of the Interior 

EA Environmental Assessment 

EDZ Extended Drilling Zone 

EIA Energy Information Administration 

EIS Environmental Impact Statement 

EPCA Energy Policy and Conservation Act 

ESRI Environmental Systems Research Institute 

EUR Estimated Ultimate Recovery 

FDGC Federal Geographic Data Committee 

FEIS Final Environmental Impact Statement 

GCDB Geographic Coordinate Database 

GGR Greater Green River 

GGRB Greater Green River Basin 

GIS Geographic Information System 

GOR Gas to Oil Ratio 

LGR Liquids to Gas Ratio 

LR Legacy Rehost 

MFP Management Framework Plan 

MMS Minerals Management Service 

NA Non-Associated natural gas 

NEPA National Environmental Policy Act 

NF National Forest 

NGLs Natural Gas Liquids 

NHRP National Register of Historic Places 

NLA No Leasing, Administrative 

NLA/LUP No Leasing, Administrative/Land Use Planning 

NLS No Leasing, Statutory or Executive Order 

NPC National Petroleum Council 

A1-1
Appendix 1 

Acronyms and Abbreviations 

NSO No Surface Occupancy 

PLSS Public Land Survey System 

RA Recreation Areas 

RMP Resource Management Plan 

ROD Record of Decision 

ROW Right-of-Way 

RPD Reserves and Production Division of the EIA 

SLT Standard Lease Terms 

SUPO Surface Use Plan of Operations 

Tcf Trillion cubic feet of natural gas 

TL Timing Limitation 

TLS Timing Limitation Stipulation 

TPS Total Petroleum System 

URA Ultimate recovery appreciation 

USDA United States Department of Agriculture 

USDA-FS U.S. Department of Agriculture-Forest Service 

USFWS United States Fish and Wildlife Service 

USGS United States Geologic Survey 

WRAs Wilderness Reinventory Areas 

A1-2
Appendix 2 

Glossary of Terms 

APPENDIX 2 

GLOSSARY OF TERMS 

-AAccess Probability: The probability, expressed as a decimal fraction, of sufficient access 

(political and physical) to a particular assessment unit within a given time frame for the activities 

necessary to find an accumulation of minimum size and to add its volume to proved reserves. 

The time frame for this assessment is 30 years. 

Accumulation: Consists of two types: conventional and continuous. A conventional 

accumulation is an individual producing unit consisting of a single pool or multiple pools of 

petroleum grouped on, or related to, a single structural or stratigraphic feature. A continuous 

accumulation is also an individual producing unit but has a really extensive pool or pools of 

petroleum not necessarily related to structural or stratigraphic features. 

Affected Environment: Surface or subsurface resources (including social and economic 

elements) within or adjacent to a geographic area that could potentially be affected by oil and gas 

activities; the environment of the area to be affected or created by the alternatives under 

consideration. (40 Code of Federal Regulations (CFR) 1502.15) 

Alternative: A combination of management prescriptions applied in specific amounts and 

locations to achieve a desired management emphasis as expressed in goals and objectives. One of 

several policies, plans, or projects proposed for decision-making. An alternative need not 

substitute for another in all respects. 

Alternative, No Action: An alternative that maintains established trends or management 

direction. 

Application: A written request, petition, or offer to lease lands for the purpose of oil and gas 

exploration and/or the right of extraction. 

Application for Permit to Drill (APD): An application to drill a well submitted by a lessee or 

operator to the BLM. The APD consists of a Drilling Plan that discusses downhole specifications 

and procedures (reviewed by the BLM) and a Surface Use Plan of Operations (SUPO) that 

examines surface uses, including access roads, well site layout, cut and fill diagrams, reclamation 

procedures, production facility locations, etc. (reviewed by the surface-managing agency). The 

approved APD is a contract between the operator and the Federal government and cannot be 

changed or modified unless authorized by the BLM and the surface-managing agency. 

Aquifer: (1.) A layer of material that contains water. (2.) The part of a water-drive reservoir that 

contains the aquifer. 

Archeological/historic site: A site that contains either objects of antiquity or cultural values 

relating to history and/or prehistory that warrant special attention. 

Assessment Unit Probability: Represents the likelihood, expressed as a decimal fraction, that, 

in a given assessment unit, at least one undiscovered accumulation of a selected minimum size 

A2-1
Appendix 2 

Glossary of Terms 

exists that has the potential for its volume to be added to proved reserves in a given time frame. 

The assessment unit probability is the product of the probabilities of the three geologic attributes 

(charge, rocks, and timing) and the probability of access. 

Associated/Dissolved Gas: Natural gas that occurs in an oil accumulation, either as a free gas 

cap or in solution; synonymous with gas in oil accumulations. 

-BBarrels of Oil Equivalent (BOE): A unit of petroleum volume in which the gas portion is 

expressed in terms of its energy equivalent in barrels of oil. For this assessment, 6,000 cubic feet 

of gas equals 1 BOE. 

Basin: 1. A depressed area with no surface outlet. 2. A low in the Earth’s crust of tectonic origin 

in which sediments have accumulated. 

Big Game: Larger species of wildlife that are hunted, such as elk, deer, bighorn sheep, and 

pronghorn antelope. 

Big Game Winter Range: An area available to and used by big game (large mammals normally 

managed for sport hunting) through the winter season. 

Buffer Zone: 1. An area between two different land uses that is intended to resist, absorb, or 

otherwise preclude developments or intrusions between the two use areas. 2. A strip of 

undisturbed vegetation that retards the flow of runoff water, causing deposition of transported 

sediment 

Bureau of Land Management: The Department of the Interior agency responsible for managing 

most Federal onshore subsurface minerals. It also has surface management responsibility for 

Federal lands designated under the Federal Land Policy and Management Act of 1976. 

-CCandidate Species: 1. A species for which substantial biological information exists on file to 

support a proposal to list it as endangered or threatened, but for which no proposal has yet been 

published in the Federal Register. The list of candidate species is revised approximately every 

two years in the Notice of Review. 2. Any species not yet officially listed, but undergoing a status 

review or proposed for listing according to Federal Register notices published by the Secretary of 

the Interior or the Secretary of Commerce. 

Casing: Steel pipe placed in an oil or gas well to prevent the hole from caving. 

Cell: A subdivision or area within an assessment unit having dimensions related to the drainage 

areas of wells (not to be confused with finite-element cells). Three categories of cells are 

recognized: cells tested by drilling, untested cells, and untested cells having potential to provide 

additions to reserves within the forecast span of the assessment. A continuous-type assessment 

unit is a collection of petroleum-containing cells. 

Completion: The activities and methods to prepare a well for production. Includes installation of 

equipment for production from an oil or gas well. 

A2-2
Appendix 2 

Glossary of Terms 

Composite Total Petroleum System: A mappable entity encompassing all or a portion of two 

or more total petroleum systems. Composite total petroleum systems are used when 

accumulations within an assessment unit are assumed to be charged by more than one source 

rock. 

Continuous-Type Accumulation: A petroleum accumulation that is pervasive throughout a 

large area, that is not significantly affected by hydrodynamic influences, and for which the chosen 

methodology for assessment of sizes and number of discrete accumulations is not appropriate. 

Continuous-type accumulations lack well-defined down-dip water contacts. The terms 

“continuous-type accumulation” and “continuous accumulation” are used interchangeably. 

Controlled Surface Use (CSU): Allowed use and occupancy (unless restricted by another 

stipulation) with identified resource values requiring special operational constraints that may 

modify the lease rights. CSU is used as an operating guideline, not as a substitute for NSO or 

Timing Lease (TL) stipulations. 

Conventional Accumulation: A discrete accumulation, commonly bounded by a down-dip 

water contact that is significantly affected by the buoyancy of petroleum in water. This geologic 

definition does not involve factors such as water depth, regulatory status, or engineering 

techniques. 

Council on Environmental Quality (CEQ): An advisory council to the President established by 

the National Environmental Policy Act of 1969. It reviews Federal programs for their effect on 

the environment, conducts environmental studies, and advises the President on environmental 

matters. 

Crucial Winter Range: Winter habitat on which a wildlife species depends for survival. 

Because of severe weather conditions or other limiting factors, no alternative habitat would be 

available. 

Cultural Resources: Those fragile and nonrenewable physical remains of human activity, 

occupation, or endeavor reflected in districts, sites, structures, buildings, objects, artifacts, ruins, 

works of art, architecture, burial mounds, petroglyphs, and natural features that were of 

importance in past human events. These resources consist of (1) physical remains; (2) areas 

where significant human events occurred, even though evidence of the event no longer remains; 

and (3) the environment immediately surrounding the resource. Cultural resources are commonly 

discussed in terms of prehistoric and historic values; however, each period represents a part of the 

full continuum of cultural values from the earliest to the most recent. 

Cumulative Petroleum Production: Reported cumulative volume of petroleum that has been 

produced. Cumulative oil, cumulative gas, and cumulative production are sometimes used as 

abbreviated forms of this term. 

-DDirectional Drilling: The intentional deviation of a wellbore from vertical to reach subsurface 

areas off to one side from the drilling site. 

A2-3
Appendix 2 

Glossary of Terms 

-EEndangered Species: As defined in the Federal Endangered Species Act, any species that is in 

danger of extinction throughout all or a significant portion of its range. For terrestrial species, the 

U.S. Fish and Wildlife Service determines endangered status. 

Environmental Assessment (EA): A public document for which a Federal agency is responsible 

that serves to: (1) briefly provide sufficient evidence and analysis for determining whether to 

prepare an Environmental Impact Statement (EIS) or a finding of no significant impact; (2) help 

an agency comply with the NEPA when no EIS is necessary; and (3) facilitate the preparation of 

an EIS when one is necessary. An EA includes brief discussions of the need for the proposal and 

of the environmental impacts of the proposed action and other alternatives. 

Environmental Impact Statement (EIS): A written analysis of the impacts on the natural, 

social, and economic environment of a proposed project or resource management plan. 

Estimated Ultimate Recovery (EUR): The total expected recoverable volume of oil, gas, and 

natural gas liquids production from a well, lease, or field under present economic and engineering 

conditions; synonymous with total recovery. 

-FFederal Land: For the purpose of the EPCA study, land owned by the United States, without 

reference to how the land was acquired or which Federal agency administers the surface; includes 

mineral estates underlying private surface. 

Field: A production unit consisting of a collection of oil and gas pools that, when projected to 

the surface, form an approximately contiguous area that can be circumscribed. 

Field Growth: The increases in known petroleum volume that commonly occur as oil and gas 

fields are developed and produced; synonymous with reserve growth. 

Forecast Span: A specified future time span in which petroleum accumulations have the 

potential to provide additions to reserves. A 30-year forecast span is used in the USGS 

assessments, which affects (1) the minimum undiscovered accumulation size, (2) the number of 

years in the future that reserve growth is estimated, (3) economic assessments, (4) the 

accumulations that are chosen to be considered, and (5) the risking structure as represented by 

access risk. 

Forest Plan: A plan for a unit of the National Forest system that provides for USDA-FS 

administered lands in the planning area included. 

Forest Service (USDA-FS): The agency of the United States Department of Agriculture 

responsible for managing National Forests and Grasslands under the Multiple Use and Sustained 

Yield Act of 1960. 

-GGas Accumulation: An accumulation with a gas to oil ratio of 20,000 cubic feet/barrel or 

greater. 

A2-4 
Appendix 2 

Glossary of Terms 

Gas in Gas Accumulations: Gas volumes in gas accumulations. 

Gas in Oil Accumulations: Gas volumes in oil accumulations. 

Gas to Oil Ratio (GOR): The ratio of gas to oil (in cubic feet/barrel) in an accumulation. GOR 

is calculated using known gas and oil volumes at surface conditions. 

Geographic Information System (GIS): In the strictest sense, a computer system capable of 

assembling, storing, manipulating, and displaying geographically referenced information, i.e., 

data identified according to their locations. 

Geologic Province: A USGS-defined area having characteristic dimensions of perhaps hundreds 

to thousands of kilometers encompassing a natural geologic entity (for example, a sedimentary 

basin, thrust belt, or delta) or some combination of contiguous geologic entities. 

Geospatial: Information that identifies the geographic location and characteristics of natural or 

constructed features and boundaries on the earth. This information may be derived from remote 

sensing, mapping, and surveying technologies, or from other sources. 

Grown Petroleum Volume: Known petroleum volume adjusted upward to account for future 

reserve growth. Thirty years of reserve growth is considered for the USGS assessments. 

-HHabitat: A specific set of physical conditions that surround a single species, a group of species, 

or a large community. In wildlife management, the major components of habitat are considered 

to be food, water, cover, and living space. 

-I-

-J-

-KKnown Petroleum Volume: The sum of cumulative production and remaining reserves as 

reported in the databases used in support of an assessment. Also called estimated total 

recoverable volume (sometimes called "ultimate recoverable reserves" or "estimated ultimate 

recovery"). 

-LLandscape: A relatively large area of land with common climate, geology, and soils containing 

predictably occurring terrain features such as slopes, drainage channels, rock outcrops, etc. 

Lease: An authorization to possess and use public land for a period of time sufficient to amortize 

capital investments in the land. 

A2-5
Appendix 2 

Glossary of Terms 

Lease Stipulations: See Stipulations. 

Liquids to Gas Ratio (LGR): Ratio of total petroleum liquids (including oil, condensate, and 

natural gas liquids) to gas (in barrels/million cubic feet) in a gas accumulation. The LGR is 

calculated using known petroleum liquids and gas volumes at surface conditions. This ratio is 

used to assess the liquid co-products associated with undiscovered gas in gas accumulations. 

-MMineral: Organic and inorganic substances occurring naturally, with characteristics and 

economic uses that bring them within the purview of mineral laws; a substance that may be 

obtained under applicable laws from public lands by purchase, lease, or pre-emptive entry. 

Minimum Accumulation Size: The smallest accumulation size (volume of oil in oil 

accumulations or volume of gas in gas accumulations) that is considered in the assessment 

process for conventional accumulations. 

Minimum Petroleum System: The mappable part of a total petroleum system for which the 

presence of essential elements has been proved by discoveries of petroleum shows, seeps, and 

accumulations. 

Minimum Total Recovery Per Cell: The smallest total recovery per cell (volume of oil or gas) 

that is considered in the assessment process for continuous-type accumulations. 

Mitigation: Includes the following: 

(1) Avoiding an impact altogether by not taking a certain action or parts of an action.

(2) Minimizing impacts by limiting the degree of magnitude of the action and its 

implementation. 

(3) Rectifying the impact by repairing, rehabilitating, or restoring the affected 

environment. 

(4) Reducing or eliminating the impact over time by preservation and maintenance 

operations during the life of the action. 

(5) Compensating for the impact by replacing or providing substitute resources or 

environments. 

Monitoring: The orderly collection, analysis, and interpretation of resource data to evaluate 

progress toward meeting resource management objectives. 

-NNational Environmental Policy Act (NEPA): The law that requires a process to assess and 

document the environmental and social impacts of federal actions. This act establishes policy, 

sets goals, and provides different ways to carry out the policy. 

A2-6
Appendix 2 

Glossary of Terms 

National Forest: A forest or weathershed reservation that is administered by the United States 

Department of Agriculture-Forest Service for multiple uses, including grazing, logging, and 

recreation. 

National Register of Historic Places (NRHP): A Federal Government list of “ . . .districts, sites, 

buildings, structures, and other objects significant in American history, architecture, archeology, 

and culture.” The National Register is maintained by the National Park Service, U.S. Department 

of the Interior, and is published in its entirety in the Federal Register each year in February. 

Natural Gas Liquids (NGL): Petroleum that occurs naturally as a gas in the reservoir, but that 

is a liquid under surface conditions. Natural gas liquids are typically reported separately from 

crude oil. 

Natural Gas Liquids to Gas Ratio (for oil accumulations): Ratio of natural gas liquids to gas 

(in barrels/million cubic feet) in an oil accumulation, calculated using known natural gas liquids 

and gas volumes at surface conditions. This ratio is used to assess the natural gas liquids 

associated with undiscovered gas in oil accumulations. 

Non-Associated Gas: Natural gas that occurs in a gas accumulation; synonymous with gas in 

gas accumulations. 

No Surface Occupancy (NSO): A no surface occupancy area where no surface-disturbing 

activities of any nature or for any purpose are allowed. For example, construction or the 

permanent or long-term placement of structures or other facilities for any purpose would be 

prohibited in an NSO area. It is also used as a stipulation or mitigation requirement for 

controlling or prohibiting selected land uses or activities that would conflict with other activities, 

uses, or values in a given area. When used in this way, the NSO stipulation or mitigation 

requirement is applied to prohibit one or more specific types of land and resource development 

activities or surface uses in an area, while other—perhaps even similar— types of activities or 

uses (for other purposes) would be allowed. For example, protecting important rock art relics 

from destruction may require closing the area to the staking of mining claims and surface mining, 

off-road vehicle travel, construction or long-term placement of structures or pipelines, power 

lines, general purpose roads, and livestock grazing. Conversely, the construction of fences (to 

protect rock art from vandalism or from trampling or breakage by livestock), an access road or 

trail, and other visitor facilities to provide interpretation and opportunity for public enjoyment of 

the rock art would be allowed. Additionally, if there were potential and interest for leasing and 

development of leasable minerals in the area, then leases for gas and oil, coal, etc., could be 

issued with a "no surface occupancy" stipulation or mitigation requirement for the rock art site, 

which would still allow access to the leasable minerals from adjacent lands and underground. 

The term "no surface occupancy" has no relationship or relevance to the presence of people in an 

area. 

Notice: The communication of a pending Federal action; the notification to parties of Federal 

actions about to the taken. This is a part of due process. 

-OOccupancy: Actual possession and use of land in something more than a slight or sporadic 

manner. As defined as a multiple use component, it is the management of public lands for 

A2-7
Appendix 2 

Glossary of Terms 

occupancy involving the protection, regulated use, and development of lands as sites for 

economically and socially useful structures, either publicly or privately owned. 

Oil Accumulation: An accumulation with a gas to oil ratio of less than 20,000 (in cubic 

feet/barrel). 

Oil in Gas Accumulations: Oil volumes in gas accumulations. For this assessment, oil in gas 

accumulations were calculated along with other liquids rather than separately. 

Oil in Oil Accumulations: Oil volumes in oil accumulations. 

Operator: An individual, group, association, or corporation authorized to conduct, for example, 

livestock grazing or oil and gas drilling on public lands. 

-PPetroleum: A collective term for oil, gas, natural gas liquids, and tar. 

Play: A set of known or postulated oil and gas accumulations sharing similar geologic, 

geographic, and temporal properties, such as source rock, migration pathway, timing, trapping 

mechanism, and hydrocarbon type. A play may or may not differ from an assessment unit; an 

assessment unit can include one or more plays. 

Proposed Species: A species of plant or animal formally proposed by the U.S. Fish and Wildlife 

Service (USFWS) to be listed as threatened or endangered under the Endangered Species Act. 

Proved Reserves: Quantities of crude oil, natural gas, or natural gas liquids that geological and 

engineering data demonstrate with reasonable certainty (defined as 90 percent or more probable) 

to be recoverable in future years from known reservoirs under existing economic and operating 

conditions. 

Public Lands: Any land and interest in land owned by the United States that are administered by 

the Secretary of the Interior through the BLM, without regard to how the United States acquired 

ownership, except for (1) lands located on the Outer Continental Shelf and (2) lands held for the 

benefit of Indians, Aleuts, and Eskimos; includes public domain and acquired lands (see 

definitions). Vacant, unappropriated, and unreserved public lands, or public lands withdrawn by 

Executive Order 6910 of November 26, 1934, as amended, or by Executive Order 6964 of 

February 5, 1935, as amended, and not otherwise withdrawn or reserved, or public lands within 

grazing district established under Section 1 of the Act of June 28, 1934 (48 Stat. 1269), as 

amended, and not otherwise withdrawn or reserved. 

-Q-

-RRemaining Petroleum Reserves: Volume of petroleum in discovered accumulations that has 

not yet been produced. Remaining reserves is sometimes used as an abbreviated form of this 

term. 

A2-8
Appendix 2 

Glossary of Terms 

Reserve Growth: The increases in known petroleum volume that commonly occur as oil and gas 

accumulations are developed and produced; synonymous with field growth. 

Resource Management Plan (RMP): A plan that provides the basic, general direction and 

guidance for BLM-administered public lands in the planning area involved. 

Right-of-Way (ROW): A permit or easement which authorizes the use of public land for certain 

specified purposes, commonly for pipelines, roads, telephone lines, etc.; also, the lands covered 

by such an easement or permit. Does not grant an estate or any kind, only the right of use. May 

also include a site. 

Riparian Areas: The vegetation along the banks of rivers and streams and around springs, bogs, 

wet meadows, lakes, and ponds. 

Roadless: Refers to an absence of roads that have been constructed and maintained by 

mechanical means to ensure regular and continuous use. 

Roads: Vehicle routes that have been improved and maintained by mechanical means to ensure 

relatively regular and continuous use. (A way maintained strictly by the passage of vehicles does 

not constitute a road.) 

-SSense of Place: Sense of place offers a holistic interpretation of a geographic place. It 

synthesizes a complex grouping of meanings, symbols, values, and feelings associated with a 

particular locality. It can include social, political, economic, aesthetic, occupational, biological, 

physical, etc. information, which can be drawn on an individual, community, and/or regional 

basis. Sense of place combines (1) contemporary (present-day) attachment, (2) traditional 

cultural use and attachment (perhaps by American Indians or other cultural/ethnic groups), and 

(3) cultural and heritage sites, properties, and districts. 

Shapefile: GIS file format usable with ESRI (such as ArcView) and other commercial GIS 

software. It is a nontopological data structure that does not explicitly store topological 

relationships. However, unlike other simple graphic data structures, one or more rings represent 

shapefile polygons. A ring is a closed, non-self-intersecting loop. This structure can represent 

complex structures, such as polygons, that contain “islands.” The vertices of a ring maintain a 

consistent, clockwise order so that the area to the right, as one “walks” along the ring boundary, is 

inside the polygon, while the area to the left is outside the polygon. 

Split Estate: Federal mineral estate administered by the BLM, which is under either private 

lands, State lands, or lands administered by another Federal agency. On split estate lands, the 

surface owner or managing agency controls the surface uses but the mineral estate is the 

dominant estate. However, the BLM coordinates with surface owners on mineral leasing and 

development. In a few cases, the BLM administers the surface, but the minerals are owned by the 

State or a private entity. 

A2-9
Appendix 2 

Glossary of Terms 

Stipulations* : Conditions, promises, or demands added to a lease when the environmental and 

planning record demonstrates the necessity for the stipulations. Stipulations, as such, are neither 

“standard” nor “special”; they are a necessary modification of the terms of the lease. In order to 

accommodate the variety of resources encountered on Federal lands, stipulations are categorized 

as to how the stipulation modifies the lease rights, not by the resource(s) to be protected. What, 

why, and how this mitigation/protection is to be accomplished is determined by the land 

management agency through land use planning and NEPA analysis. 

If, upon weighing the relative resource values, uses, and/or users, conflict with oil and gas 

operations is identified that cannot be adequately managed and/or accommodated on other lands, 

then a lease stipulation is necessary. Land use plans serve as the primary vehicle for determining 

the necessity for lease stipulations. Documentation of the necessity for a stipulation is disclosed 

in planning documents or through site-specific analysis. Land use plans and/or NEPA documents 

also establish the guidelines under which future waivers, exceptions, or modifications may be 

granted. 

Substantial modification or waiver of stipulations subsequent to lease issuance is subject to public 

review for at least a 30-day period in accordance with Section 5102.f of the Federal Onshore Oil 

and Gas Leasing Reform Act of 1987 (FOLRA). Stipulations may be necessary if the authority to 

control the activity on the lease does not already exist under laws, regulations, or orders. An 

authorized Federal officer has the authority to modify the site location and design of facilities, 

control the rate of development and timing of activities, and require other mitigation under 

standard lease term. The necessity for individual lease stipulations is documented in the lease-file 

record with reference to the appropriate land use plan or other leasing analysis document. The 

necessity for exceptions, waivers, or modifications is documented in the lease-file record through 

reference to the appropriate plan or other analysis. 

Study Areas: The Paradox/San Juan, Uinta/Piceance, Greater Green River, and Powder River 

Basins, and the Montana Thrust Belt, which were selected as the resource provinces of the study 

and comprise the areas of these resource provinces underlain by oil and/or natural gas resources 

based upon USGS analysis. 

Subsurface Allocation: An allocation of potential additions to reserves to land entities based on 

subsurface ownership of mineral rights. 

Surface Allocation: An allocation of potential additions to reserves to land entities based on 

surface ownership. 

Sweet Spot: An area within a continuous-type deposit where production characteristics are 

relatively more favorable. 

-T-

* Taken from the booklet, “Uniform Format for Oil and Gas Lease Stipulations,” prepared by the Rocky 

Mountain Regional Coordinating Committee in March 1989. These guidelines were developed by the 

BLM and USDA-FS. 

A2-10
Appendix 2 

Glossary of Terms 

Technically Recoverable Resources: I n-place resources that are producible using current 

recovery technology but without reference to economic profitability. These are oil and natural 

gas resources that may be produced at the surface from a well as a consequence of natural 

pressure within the subsurface reservoir, artificial lifting of oil from the reservoir to the surface, 

and the maintenance of reservoir pressure by fluid injection. These resources are generally 

conceived as existing in accumulations of sufficient size to be amenable to the application of 

existing recovery technology. 

Timing Limitation: Prohibits surface use during specified time periods to protect identified 

resource values. The stipulation does not apply to the operation and maintenance of production 

facilities unless the findings of analysis identify the continued need for such mitigation and 

demonstrate that less stringent, project-specific mitigation measures would be insufficient. Also 

called a Seasonal Restriction. 

Total Petroleum System (TPS): A mappable entity encompassing genetically related petroleum 

that occurs in seeps, shows, and accumulations (discovered or undiscovered) that have been 

generated by a pod or by closely related pods of mature source rock, together with the essential 

mappable geologic elements (source, reservoir, seal, and overburden rocks) that controlled 

fundamental processes of generation, migration, entrapment, and preservation of petroleum. 

Total Recovery: The total expected recoverable volume of oil, gas, and natural gas liquids 

production from a well, lease, or field under present economic and engineering conditions; 

synonymous with estimated ultimate recovery. 

-UUltimate Recovery Appreciation (URA): The generally observed increase of Estimated 

Ultimate Recovery (EUR) over time. 

Undiscovered Petroleum Resources: Resources postulated from geologic information and 

theory to exist outside of known oil and gas accumulations. 

USGS-Assessed Petroleum Volumes: The quantities of oil, gas, and natural gas liquids that 

have the potential to be added to reserves within some future time frame, which for this 

assessment is 30 years. The USGS assessed petroleum volumes include both those from 

undiscovered accumulations, whose sizes are greater than or equal to the selected minimum 

accumulation size, and those from the reserve growth of fields already discovered. 

-V-

-WWetlands: Permanently wet or intermittently flooded areas where the water table (fresh, saline, 

or brackish) is at, near, or above the soil surface for extended intervals; where hydric wet soil 

conditions are normally exhibited; and where water depths generally do not exceed two meters. 

Marshes, shallows, swamps, muskegs, lake bogs, and wet meadows are examples of wetlands. 

Wilderness: A Congressionally designated area of undeveloped Federal land retaining its 

primeval character and influence, without permanent improvement or human habitation, that is 

A2-11
Appendix 2 

Glossary of Terms 

protected and managed so as to preserve its natural conditions and that (1) generally appears to 

have been affected primarily by the forces of nature, with the imprint of man's work substantially 

unnoticeable; (2) has outstanding opportunities for solitude or a primitive and unconfined type of 

recreation; (3) has at least 5,000 acres of land or is of sufficient size as to make practicable its 

preservation and use in an unimpaired condition; and, (4) may also contain ecological, geological, 

or other features of scientific, educational, scenic, or historical value. 

Wildlife: All living vertebrate and invertebrate fauna that exist or potentially exist in an area. 

Withdrawal: An action that restricts the disposition of public lands and that holds them for 

specific public purposes; also, public lands that have been dedicated to public purposes (for 

example, recreation sites, office or warehouse sites, etc.). 

A2-12
Appendix 3 

Land Status Methodology 

APPENDIX 3 

LAND STATUS METHODOLOGY 

For purposes of the EPCA project, spatial data themes were created that define various ownership 

characteristics and categories for lands within the play boundaries. The final data sets were 

rendered to delineate both surface and subsurface U.S. rights. To accomplish this, ownership 

cases, extracted from the BLM's LR-2000 Case Recordation and Status Databases, were 

processed and used to created polygon themes for the project (Figure A3-1). 

Figure A3-1 Schematic of BLM’s Primary Land Records Databases 

The primary information that defines U.S. interests in parcels of land are data elements associated 

with various case categories and land transactions recorded and maintained in the BLM's LR2000 Case Recordation and Status Databases. The mapped case land records extracted fall within 

four general categories: 

Land Disposals, including patents, grants, deeds, land sales, and all other transactions that 

conveyed Federal ownership rights in lands from the Federal Government. 

Acquired Lands, including lands that were re-acquired by the United States under various 

legal authorities. 

Land Exchanges, including lands exchanged between the Federal Government and other 

parties. 

Quiet Title Cases, including all records established to cure title and quiet adverse claims. 

These four major categories formed the basis to extract records from the BLM's databases. The 

four queries were processed against both the Status and Case Recordation Systems. Due to 

formatting differences between the two databases, the resulting polygon attributes contained in 

A3-1 
Appendix 3 

Land Status Methodology 

the GIS shape files varied slightly. Additionally, in some case records extracted from the Case 

Recordation system, U.S. rights were not readily available but were determined as accurately as 

possible through interpretation from land records obtained at BLM State and field offices. 

The polygon boundaries created through processing reflect the geometry as described by aliquot 

part description. Lands described by lot or tract surveys were processed against the BLM Legal 

Land Description (LLD) file to convert the lot references to nominal aliquot descriptions for 

mapping purposes. Depending on the actual survey type and geometry, the resulting polygon 

may contain a degree of generalization. Additionally, the BLM record systems do not contain 

individual records for public domain lands. The location of these lands was determined through 

various polygon-processing steps described below. The data elements for the attribute fields 

contained in the shape files produced from each of the LR-2000 databases are shown in Table 

A3-1. 

Status Data Attributes* Case Recordation Attributes* 

Shape Meridian 

Meridian Township 

Township Range 

Range Section 

Section Surveytype 

Survey Type Aliquot 

Aliquot Serialnumb 

Adminagenc Surveynumb 

County Name 

State Percentint 

Serialnumb Price 

Docid Acres 

Patent_num Dispositio 

Case_type Casetype 

Usright1 Commodity 

Usright2 Expiredate 

Usright3 Expireyear 

Usright4 Effectdate 

Patentissu (mm/dd/yy) Royaltyrt 

Patentiss1 (year) Geoname 

Acres Hbp 

Patentee Or 

Id Id 

*Note: Data fields were populated if data is entered in the Status or Case 

Recordation database. If U.S. rights are recorded in the US Rights field, they 

were included in the Commodity field. 

Table A3-1 Data Elements, LR-2000 Database 

The data simplification process was completed through numerous steps that combined data 

associated with each of the four broad record categories referenced above using the following 

processing steps, shown for an example from the Powder River Basin: 

A3-2 
Appendix 3 

Land Status Methodology 

1. A Public Land Survey System (PLSS) grid digitized from USGS 7.5-minute quadrangle maps 

was used as the cadastral reference framework and contains shapefile coverages that define both 

townships and sections. For example, lands that fall within the geographic extent of the Powder 

River Basin were acquired in 1803 under the Louisiana Purchase. All surface and subsurface 

rights belonged to the United States of America. 

After the PLSS base was loaded, a master polygon (Figure A3-2) was created to represent the 

disposition of the lands at the time of the original purchases and annexations by which the United 

States acquired land. 

Figure A3-2 Master Polygon 

2. The next step involved processing textual legal land descriptions against the section shape file by 

subdividing according to the survey rules embedded in the CarteView product1. Table A3-2 

shows a typical input file. 

Table A3-2 Typical CarteView Input File 

3. After the records from the Status and Case Recordation databases were processed, the resulting 

polygon themes were re-attributed to allow for a merge between the two data sets. The polygons 

were then overlaid on the Master Polygon to establish the location of lands where ownership left 

1

 A product available through Premier Data Services, Inc. 

A3-3 
Appendix 3 

Land Status Methodology 

the Federal government by virtue of patent, grant, or other title transfer authority. The resulting 

coverages are represented in Figure A3-3. 

The yellow polygons shown on Figure A3-3 represent lands that remain in the public domain 

with all surface and subsurface rights managed by the BLM. These public domain lands were 

then converted to a polygon and attributed to show the current disposition of the U.S rights. 

Figure A3-3 Public Domain Lands 

4. The next step involved constructing a series of queries against the U.S. rights data associated with 

lands that were disposed of by virtue of various title transfers. This query process involved 

intensive comparison against the attribute tables in the spatial databases. The results of these 

processes allowed definition of all lands where subsurface oil and gas rights are owned by the 

United States. 

Figure A3-4 illustrates the distribution of subsurface mineral ownership within a four-township 

area. The parcels shaded gray represent patented lands where the United States has retained 

rights to the mineral or oil and gas estate. 

A3-4
Appendix 3 

Land Status Methodology 

Figure A3-4 Retained U.S. Rights to Mineral or Oil and Gas Estate 

5. Next, any surface management agencies or state ownership were defined. These determinations 

were made by completing a series of queries against the ownership fields in the shape files. An 

example of the results of this query is shown in Figure A3-5, where the parcels shaded blue 

represent lands that were granted to the State of Wyoming. 

Figure A3-5 Defining Ownership 

A3-5 
Appendix 3 

Land Status Methodology 

The final processing step was to dissolve the individual parcels into ownership categories that 

define the surface and mineral estates. Figure A3-6 shows the surface management agencies and 

how land ownership is distributed within an area of the Powder River Basin in Wyoming. 

Figure A3-6 Surface Management View 

In contrast to the surface management view, the mineral estate (shown in Figure A3-7) covers the 

same area and yields a much different picture. The yellow areas represent lands where the 

Federal government owns oil and gas rights. 

Figure A3-7 Subsurface Oil and Gas Ownership View 

A3-6 
Appendix 3 

Land Status Methodology 

Through the above-described procedure, a detailed assessment of the land status was performed. 

To facilitate the analytical portion of the project, a simplified version of the status data was 

created, based on the allocation of the detailed land status to the fundamental Federal surface 

management agency (i.e., BLM, USDA-FS, etc.)2

. Maps of the Federal land status for the study 

areas are presented in Section 2 in Figures 2a through Figure 2e. 

The derivation of land status, while complex given the amount of recordation examined, was 

straightforward in process. However, the following limitations do exist: 

The data sets created from the processes described above reflect the legal land descriptions 

contained in the BLM databases. Case files were not consulted in the process. This procedure 

did generate error logs, especially if legal land descriptions had not been properly formatted 

according to BLM's published LR-2000 standards. The errors created in this process are believed 

to have minimal impact. 

If a legal description referenced a small survey lot or tract by number, a nominal location was 

mapped through a PROCESS that referenced the BLM's LLD file. This file is limited to a 40-

acre description and carries a minor degree of generalization in complex areas. 

The BLM Case Recordation System is not consistently populated with U.S. rights data. To 

overcome this, the split estate ownership was established from Case Recordation Data by 

contacting BLM State and field offices. This process results in a minor degree of generalization. 

Some status information derived from GIS coverages was obtained from multiple sources, 

resulting in the creation of some sliver polygons during the spatial processing and merging of 

these data. 

These are an artifact of the differing sources of data and may be present in certain ownership 

themes; however, their impact on the analyses is minimal. 

The processing of the PLSS data, which are variably sourced, resulted in edge matching across 

State boundaries. This is believed to have a minimal impact on the analyses. 

The detailed and simplified land ownership databases are presented, by study area, on the CD 

accompanying this report. 

A3-7

2 
Appendix 4 

Lease Stipulation Data Preparation 

APPENDIX 4 

LEASE STIPULATION DATA PREPARATION 

The bulk of the data preparation consisted of data gathering, data digitization, and compilation of 

the gathered data in a multi-layered GIS format (ESRI shapefiles). Federal Geographic Data 

Committee Standards (FGDC)-compliant metadata for the resulting GIS layers were also created. 

GIS coverages from surface management agency land status, stipulations, and the analyses, as 

well as the associated metadata, are presented on the CD-ROMs accompanying this report. 

Where necessary, the shapefiles obtained from the Federal land management agencies were 

processed using ArcGIS software by matching specific leasing stipulations found in the guidance 

documents. 

The EPCA inventory is limited to those Federal lands within the aggregate resource play 

boundaries of the five study areas, which are based on geology as defined in the USGS National 

Assessment of Oil and Gas Resources. The land status and stipulation shapefiles, which 

correspond to Federal land management agency jurisdiction boundaries, were “clipped” using the 

GIS to the appropriate study boundary. Some of the shapefiles fell into multiple study areas, so 

the clipping process was repeated for each area. The attribute tables of the compiled shapefiles 

were then queried for unique leasing stipulation values. The query results were then saved as 

separate polygon shapefiles. Each shapefile represents a unique stipulation value. 

The following discussion of the specific data preparation steps uses the Paradox/San Juan Basin 

study area as an example. 

1. The first step entails loading the study area (union of resource plays) boundary 

shapefile and the compiled stipulation shapefile into ArcGIS (Figure A4-1). 

Figure A4-1 Multi-Stipulation Polygon and Study Area Boundary 

2. The next step in this process is to “clip” or cut the compiled stipulation shapefile to 

the study boundary. Figure A4-2 shows how this GIS coverage partially falls outside 

A4-1
Appendix 4 

Lease Stipulation Data Preparation 

of the study boundary. Figure A4-3 shows the GIS coverage after it has been 

clipped. 

Figure A4-2 Example of Shapefile Extending Over Study Area Boundary 

Figure A4-3 Example of Shapefile after Clipping to Study Area Boundary 

3. The compiled stipulation shapefile is then queried for unique stipulation attributes 

values as shown in the ArcGIS Query Builder (Figure A4-4). For this example, all 

polygons covered by the leasing stipulation “Critical Big Game Habitat” were 

selected. The highlighted rows in the attribute table (Figure A4-5) show which 

records are selected. The polygons associated with the selected attributes are 

highlighted in Figure A4-6 (purple outline). 

A4-2
Appendix 4 

Lease Stipulation Data Preparation 

Figure A4-4 Query in ArcGIS for all “Critical Big Game Habitat” 

Figure A4-5 Attribute Table Showing all “Critical Big Game Habitat” Polygons 

A4-3 
Appendix 4 

Lease Stipulation Data Preparation 

Figure A4-6 Polygons Selected by Query as “Critical Big Game Habitat” 

4. Using the ArcGIS function “Create layer from Selected Features,” a new shapefile is 

created that contains only polygons labeled with the attribute “Critical Big Game 

Habitat” (Figure A4-7). Figure A4-8 shows the new shapefile that is created. 

Figure A4-7 Creating New Shapefile from Selected Attributes 

A4-4 
Appendix 4 

Lease Stipulation Data Preparation 

Figure A4-8 New Shape File Representing Land with Leasing Stipulation for

 “Critical Big Game Habitat” 

For certain stipulations, such as steep slopes, for which GIS data were not available from the 

BLM or Forest Service offices, shapefiles were created from available data in conformance with 

stipulation requirements. For example, a typical steep slope stipulation impacts leasing in areas 

where slopes exceed 40 percent. Polygon themes were created from slope data derived from 

USGS 1:24,000 Digital Elevation Models (DEMs). These raster data sets contain elevation 

information on a 30-meter grid spacing. 

The USGS DEMs were first clipped to the BLM or Forest Service jurisdictional area. In 

situations where more than one agency had the same stipulations, the digital elevation model 

(DEM) was clipped to the agencies’ combined jurisdictional area. A raster coverage was then 

created containing slope percentage data as calculated by ArcGIS. This coverage was then 

queried to isolate the areas covered by the stipulation (i.e., all areas equal to or steeper than 40 

percent). The selected raster data was then converted to a vector polygon coverage, and the 

coverage was coded and attributed as described above. Figure A4-9 shows the creation of steep 

slope coverages. The 30-meter USGS DEM for this portion of the Uinta Basin is shown in 

shades of beige. The red theme at the bottom center of the figure represents the polygon shapefile 

showing areas with a greater than 40 percent slope. 

A4-5
Appendix 4 

Lease Stipulation Data Preparation 

Figure A4-9 Creation of Steep Slope Restriction Coverages 

Following the above procedures, the GIS shapefiles of the stipulations were coded with their 

respective descriptions from the various land use plans. These stipulations are listed in Appendix 

9. 

A4-6
Appendix 5 

USGS Geological Survey Methodology 

APPENDIX 5

U.S. GEOLOGICAL SURVEY METHODOLOGY FOR THE ASSESSMENT OF

UNDISCOVERED OIL AND GAS RESOURCES 

By U.S. Geological Survey National Assessment Review Team 

Introduction 

The USGS conducts assessments of technically recoverable undiscovered oil and gas resources of 

the onshore and State waters of the United States. The last comprehensive USGS oil and gas 

assessment was completed in 1995, and comprises the onshore and State waters portion of 71 

geologic provinces (Gautier and others, 1996). In 1999, the USGS initiated a new, six-year plan 

to produce incremental assessments of the 25 most significant U.S. oil and gas provinces. 

To meet the requirements of Section 604 of the EPCA, the USGS reorganized the priority list for 

the new re-assessments. For this EPCA report, new assessments were conducted for the UintaPiceance Basin, San Juan Basin, Montana Thrust Belt, Powder River Basin, and Greater Green 

River Basin. The 1995 assessment results were used for the Paradox Basin. The general 

assessment methodology has not changed from the 1995 assessments; however, some refinements 

have been made to accommodate increased geologic understanding of the occurrence of resources 

and more sophisticated means of capturing the range of uncertainty inherent in these variables. 

For example, the assessment model for continuous resources in the 1995 assessment assumed a 

homogenous distribution of oil and gas resources in a play. For the new assessments, that model 

has been replaced with an analysis of geologically controlled sweet spots of production, which 

demonstrate the geologic heterogeneity common to continuous oil or gas accumulations. The 

recognition of production sweet spots is a major advancement in the assessment of continuous 

resources. 

This report includes the assessment of undiscovered conventional and continuous 

(unconventional) oil and gas resources of these resources to surface land ownership categories in 

the five priority EPCA provinces listed above: Uinta-Piceance Basin, Paradox-San Juan Basins, 

Montana Thrust Belt, Powder River Basin, and Southwest Wyoming (Greater Green River 

Basin). 

Terminology 

Terminology used in this report reflects standard definitions and usage of the oil and natural gas 

industry and the petroleum resource assessment community. Several terms have been developed 

by the USGS for oil and gas assessment purposes (see Glossary in Appendix 2). The 1995 USGS 

assessment focused on the definition and assessment of geologic plays. In the latest USGS 

assessment, the focus is on understanding total petroleum systems and defining assessment units 

within total petroleum systems. The total petroleum system approach is designed to focus the 

geologic studies on the hydrocarbon source rocks, processes that create hydrocarbons, migration 

pathways, reservoirs, and trapping mechanisms. For discussion purposes in this report, the term 

play will be used throughout to represent both assessment units and plays. 

A5-1
Appendix 5 

USGS Geological Survey Methodology 

The USGS assesses two main categories of hydrocarbon occurrence: conventional and continuous 

(Figure A5). Conventional oil and gas accumulations are defined as discrete fields with welldefined hydrocarbon-water contacts, where the hydrocarbons are buoyant on a column of water. 

Conventional accumulations commonly have relatively high matrix permeabilities, have obvious 

seals and traps, and have high recovery factors. In contrast, continuous accumulations (also 

called unconventional accumulations) commonly are regional in extent, have diffuse boundaries, 

and are not buoyant on a column of water. Continuous accumulations have very low matrix 

permeabilities, do not have obvious seals and traps, are in close proximity to source rocks, are 

abnormally pressured, and have low recovery factors. The USGS assessment focused on 

understanding the geology and occurrence of continuous hydrocarbon accumulations, as the 

resource potential of these accumulations may be greater than that for conventional 

accumulations in the U.S. Included in the category of continuous accumulations are 

hydrocarbons that occur in tight reservoirs, shale reservoirs, unconventional reservoirs, basincentered reservoirs, fractured reservoirs, coal beds, hydrates, and oil shales. 

Figure A5 Conventional vs. Continuous Accumulations 

Overview of the Oil and Gas Assessment Procedure 

The assessment process is based on the characterization of the petroleum geology of each 

province. The geologists define the geologic elements of the total petroleum systems, and, in 

conjunction with an analysis of historic oil and gas production and exploration/discovery data, 

define the oil and gas plays within the provinces. The geologists then develop probability 

distributions for sizes and numbers of undiscovered conventional accumulations, or numbers of 

cells and EUR’s for continuous accumulations, using all available geologic information and 

historic oil and gas data. These distributions are then used to generate probability distributions 

for undiscovered oil and gas resources. 

A5-2
Appendix 5 

USGS Geological Survey Methodology 

Role of Geologic Information in the Assessment 

The strength of the USGS oil and gas resource assessments is the province geologists’ 

understanding of the petroleum geology of the provinces being assessed. These fundamental 

geologic studies allow new concepts and hypothetical plays to be incorporated into the 

assessment of undiscovered resources. A purely statistical approach to an assessment such as 

discovery process modeling that uses only historical data will overlook any new geologic 

concepts, models, or hypothetical plays. 

The team of geologists develops an understanding of the province petroleum geology using 

published, proprietary, and original research and data. Studying the total petroleum systems 

within a province includes: (1) identification and mapping the extent of the major hydrocarbon 

source rocks; (2) understanding the thermal evolution of each source rock, the extent of mature 

source rock, and the timing of hydrocarbon generation, expulsion, and migration; (3) estimating 

migration pathways and all forms of hydrocarbon trapping; (4) modeling the timing of structural 

development and the timing of trap formation relative to hydrocarbon migration; (5) determining 

the sequence stratigraphic evolution of reservoirs, and the presence of conventional or continuous 

reservoirs, or both; and (6) modeling the burial history of the basin and the effect burial and uplift 

has had on the preservation of conventional and continuous hydrocarbons. 

Once the total petroleum systems of the province are known in satisfactory detail, the team of 

geologists defines oil and gas plays, which represent a synthesis of all geologic information, 

including production and exploration data. The key component of this analysis is a geologic 

model for the assessment of each play. The geologic model encompasses all elements of the total 

petroleum system, and is commonly summarized by a total petroleum system events chart. 

Sources of Oil and Gas Data 

Data for domestic oil and gas fields, reservoirs, and wells are derived from commercial databases 

purchased annually by the USGS. With more than 2.5 million domestic oil and gas wells and 

40,000 oil and gas fields, the USGS has opted to purchase the data from commercial vendors 

rather than attempt to generate a comprehensive database. The oil and gas wells and production 

databases are now purchased from the IHS Energy Group (2000 a, b). Previous assessments used 

the predecessors to IHS: PetroROM Production Data (Petroleum Information/Dwights LLC, 

1999a) and the Well History Control System (Petroleum Information/Dwights LLC, 1999b). 

The USGS also relies on the NRG Associates, Inc. Significant Oil and Gas Fields of the United 

States (NRG Associates, 2001). Data from these commercial databases are subject to proprietary 

constraints, and the USGS cannot publish, share, or serve any data from these databases. 

However, derivative representations in the form of graphs and summary statistics can be prepared 

and presented for each play. The USGS, however, cannot verify the accuracy, completeness, or 

currency of data reported in commercial databases. 

The IHS production database provides oil and gas production data for wells, leases, or producing 

units (collectively called “entities” in these databases). The IHS oil and gas wells database 

provides individual well data (including data for dry holes) that include well identification, 

locations, and information on penetrated and producing formations. Oil and gas field databases 

provide location, geologic characterization, and oil and gas production data for domestic oil and 

gas fields and reservoirs. 

A5-3
Appendix 5 

USGS Geological Survey Methodology 

Additional oil and gas data are obtained, where available, from operators, state agencies, and 

other government sources, such as the U.S. Department of Energy’s Energy Information 

Administration proprietary files, publications from the former Bureau of Mines, and other 

sources. 

Assigning Accumulations and Wells to Plays 

Digital maps of plays are created using a GIS. The oil and gas play boundaries are available at 

http://energy.cr.usgs.gov/oilgas/noga. Digital play maps are used to assign oil and gas wells and 

accumulations to their respective plays, and these assignments are entered into the databases. Oil 

and gas accumulations are assigned to only one play. Wells, however, can be assigned to more 

than one play if they penetrate vertically stacked plays. Oil and gas accumulations and well 

assignments are reviewed to ensure proper assignments, identify inconsistent data, and examine 

the need for minor revisions of play boundaries. 

Historic production and exploration/discovery data are collected for each play using oil and gas 

accumulations or well assignments. Types of data retrieved include: (1) known volumes (sum of 

cumulative production and remaining reserves) of recoverable oil, gas, and natural gas liquids 

(NGL) of accumulations; (2) discovery dates of accumulations (the year the first reservoir in the 

accumulation was discovered); (3) monthly production and cumulative production of wells; (4) 

initial classification and final classification of wells (for example, new-field wildcat, 

development, producing, abandoned, and so on) of wells; and (5) completion dates of wells. 

Oil and Gas Production Data 

The historic oil and gas production data are compiled for each play so that the data from 

discovered accumulations can be used as a guide for potential undiscovered accumulations. For 

conventional plays, these data include (1) field name, (2) field discovery year or date of 

completion of the discovery well, (3) known volumes of oil, gas (non-associated and associateddissolved), and NGL, and (4) depth to the top of each reservoir. All of the production data for 

conventional assessment units are arranged in terms of oil accumulations and gas accumulations 

and sorted by size and discovery date for statistical calculations and plotting. A list of new-field 

wildcat wells and their completion dates is compiled and organized into the number of wells 

drilled per year for conventional plays. (A new-field wildcat well is an exploratory well drilled at 

least two miles from a producing field to test a separate trap.) Once organized, the number of 

wells drilled in a given year is used as a measure of exploration effort. These data are then 

combined with the production data using the discovery dates of the accumulations and the 

completion dates of the wells. 

Oil and gas production data compiled for each producing well in continuous-type plays include 

past monthly production of liquids (oil and NGL) and gas (non-associated and associateddissolved), from which EUR’s are estimated using well decline-curve analysis, the date of first 

production, and depth to the topmost perforation. A list of all wells and completion dates are 

compiled and organized. However, the number of wells drilled in a given year is not combined 

with production data, but analyzed separately. 

Co-product ratios (GOR; NGL to gas ratio; and LGR) are calculated and major commodities (oil 

or gas) are identified for each conventional accumulation. Co-product ratios are based on 

accumulation-level oil, gas, and NGL volumes. Oil and gas accumulations are treated separately; 

A5-4
Appendix 5 

USGS Geological Survey Methodology 

an oil accumulation is defined as one having a GOR less than 20,000 cubic feet/barrel whereas a 

gas accumulation has a GOR equal to or greater than 20,000 cubic feet/barrel. 

Supplemental data from individual reservoirs within the accumulations include thickness (net and 

gross), average porosity, average permeability, temperature, pressure, fluid properties (for 

example, sulfur content of oil, API gravity of oil, non-hydrocarbon gas contents), trap type, drive 

type, and well spacing. These data are combined with the data from the commercial databases to 

help refine the geologic interpretations and assessment process. 

Graphs and Statistics for Conventional Plays 

Two sets of graphs and statistics are generated for conventional plays – one set using known 

accumulation sizes as of the effective date of the assessment and one set using accumulation sizes 

that are corrected for anticipated reserve growth (grown accumulation size) within the forecast 

span of the assessment. 

The set of graphs and statistics generated for conventional plays includes sizes and number of 

accumulations with respect to discovery date and exploration effort, exploration effort through 

time, size distributions of accumulations, reservoir depth versus discovery date and exploration 

effort, co-product ratios versus reservoir depth, and a histogram of the API gravity. 

Accumulations containing less than a specified minimum volume of oil or gas (that is, the 

smallest accumulation size that is considered in the assessment process) are not included in these 

graphs or statistics. Counts of new-field wildcat wells are used as a measure of exploration effort 

for finding new accumulations. 

Assessment Input for Conventional Plays 

Critical input data for conventional plays are probability distributions for sizes and numbers of 

undiscovered oil and gas accumulations and co-product ratios. The geologists develop these 

distributions by synthesizing all petroleum systems information and historic oil and gas data. For 

hypothetical plays, the geologist may utilize an analog data set for sizes and numbers of 

discovered fields as a guide to the distributions of sizes and numbers of undiscovered fields in the 

play or assessment unit being assessed. Geologists provide information on oil and gas quality, 

range of drilling depths, and range of water depths for future economic analyses. 

Graphs and Statistics for Continuous-Type Plays 

A set of graphs and statistics comparable to that for conventional plays is generated for 

continuous-type plays, but the EUR per cell and numbers of tested cells are used rather than 

accumulation sizes and number of discovered accumulations. Tested cells of less than the 

specified minimum EUR per cell are not included in these graphs or statistics, and reserve-growth 

adjustments for cells are not incorporated. 

The set of graphs and statistics generated for continuous-type plays includes number of wells 

drilled through time (all wells as opposed to new-field wildcat wells), probability distributions of 

EUR, EUR versus production-start year and number of all wells drilled, cumulative EUR versus 

production-start year and number of wells drilled, cumulative EUR versus depth of the topmost 

perforation, and GOR versus ranked EUR. All of this information is provided to the assessor as a 

guide to generating distributions for the assessment of undiscovered resources. 

A5-5
Appendix 5 

USGS Geological Survey Methodology 

Assessment Input for Continuous Plays 

Critical input data for the continuous play assessment model include numbers of cells that have 

potential to be added to reserves, the EUR distribution for these cells, and the co-product ratios. 

For hypothetical plays, the geologist may utilize an analog data set for distribution of cell size and 

for the EUR distribution as guides to the distributions of cell sizes and EUR’s of undiscovered 

area in the play being assessed. The geologist provides information on oil and gas quality, range 

of drilling depths, and range of water depths for future economic analyses. 

USGS Assessment Review 

The province geologist must present the geology of the play and the input data to a team of USGS 

personnel for a formal review. The team consists of geologists, geophysicists, and assessment 

methodologists with broad expertise in petroleum geology, which together promotes a consistent 

geological and methodological approach to the assessment. Every aspect of the geology and 

input data are reviewed, and any changes are incorporated into the input data at this time. Once 

the input data have been finalized, the input data are ready for quantitative analysis. 

Calculation of Undiscovered Conventional and Continuous Resources 

The final reviewed assessment input forms are the basis of the quantitative calculations of 

undiscovered oil and gas resources. For conventional plays, the probability distributions for sizes 

and numbers of undiscovered accumulations and the co-product ratios provided by the assessor 

are entered into a Monte Carlo simulator and run for a specified number of iterations to provide 

distributions of undiscovered oil, gas, and NGL resources. In the 1995 assessment, a Truncated 

Shifted Pareto Distribution (Gautier and Dolton, 1996) was used for the shape of the curve for the 

distribution of sizes of oil and gas fields. For the present assessment, a Truncated Shifted 

Lognormal Distribution is used for this purpose (Charpentier and Klett, 2000). 

For continuous plays, the distributions for assessment-unit area, untested percentage of 

assessment unit area, potential percentage of untested area, and area per cell of untested cells are 

combined analytically to determine the distribution for number of potential untested cells. The 

distribution for numbers of potential untested cells EUR per cell , and the co-product ratios are 

combined using an Analytic Probability Method (Crovelli, 2000) to directly calculate the 

probability distribution of undiscovered oil and gas resources. 

Assessment Results 

The results and maps of the resource assessment of more than 90 oil and gas plays for the UintaPiceance Basin, Paradox-San Juan Basins, Greater Green River Basin, Powder River Basin, and 

the Montana Thrust Belt provinces can be downloaded from 

http://energy.cr.usgs.gov/oilgas/noga.

A5-6
Appendix 5 

USGS Geological Survey Methodology 

Interim EPCA Report and Assessment Review Team:

Schenk, Christopher J., Charpentier, Ronald R., Klett, Timothy R., Pollastro, Richard M., Cook,

Troy A., and Crovelli, Robert A.

Uinta-Piceance Assessment:

Kirschbaum, Mark A., Dubiel, Russell F., Johnson, Ronald C., Johnson, Edward A., Hettinger,

Robert D., Finn, Thomas M., Anna, Lawrence O., Henry, Mitchell, Collett, Timothy S., Roberts,

Laura N., Roberts, Stephen B., Lillis, Paul G., Rice, Cynthia A., Schmoker, James W., and

Nuccio, Vito F.

Greater Green River Assessment:

Kirschbaum, Mark A., Johnson, Ronald C., Johnson, Edward A., Hettinger, Robert D., Finn,

Thomas M., Roberts, Laura N., Roberts, Stephen B., and Lillis, Paul G.

Powder River Basin Assessment:

Flores, Romeo M., Anna, Lawrence O., and French, Christopher

Montana Thrust Belt Assessment:

Schenk, Christopher J., Potter, Christopher J., Dyman, Thaddeus S., Perry, William J., French,

Christopher, and Henry, Mitchell

San Juan Basin Assessment:

Ridgley, Jennie L., Condon, Steven M., Dubiel, Russell F., Fishman, Neil S., and Hatch, Joseph

R. 

References Cited 

Charpentier, R.R., and Klett, T.R., 2000, Monte Carlo simulation method, in U.S. Geological 

Survey World Energy Assessment Team, U.S. Geological Survey World Petroleum Assessment 

2000- description and results: U.S. Geological Survey Digital Data Series DDS-60, Chapter MC. 

Crovelli, R.A., 2000, Analytic resource assessment method for continuous (unconventional) oil 

and gas accumulations - the “ ACCESS” method: U.S. Geological Survey Open-File Report 00-

044, 34 p. 

Gautier, D.L., and Dolton, G.L., 1996, Methodology for assessment of undiscovered conventional 

accumulations, in 1995 National assessment of United States oil and gas resources--Results, 

methodology, and supporting data: U.S. Geological Survey Digital Data Series DDS-30, Release 

2 (1 CD-ROM). 

Gautier, D.L., Dolton, G.L., Takahashi, K.I., and Varnes, K.L., eds., 1996, 1995 National 

assessment of United States oil and gas resources--Results, methodology, and supporting data: 

U.S. Geological Survey Digital Data Series DDS-30, Release 2 (1 CD-ROM).

IHS Energy Group, 2000a [includes data current as of December, 1999], PI/Dwights Plus US 

Production Data: Englewood, Colo., IHS Energy Group; database available from IHS Energy 

Group, 15 Inverness Way East, D205, Englewood, Colorado 80112, U.S.A. 

IHS Energy Group, 2000b [includes data current as of December, 1999], PI/Dwights Plus US 

Well Data: Englewood, Colo., IHS Energy Group; database available from IHS Energy Group, 

15 Inverness Way East, D205, Englewood, Colorado 80112, U.S.A. 

A5-7
Appendix 5 

USGS Geological Survey Methodology 

NRG Associates, Inc., 1993, 1994, 1999, 2000, and 2001 [includes data current as of December 

31, 1992, December 31, 1993, December 31, 1998, December 31, 1999, and December 31, 2000, 

respectively], The Significant Oil and Gas Fields of the United States: Colorado Springs, Colo., 

NRG Associates, Inc.; database available from NRG Associates, Inc., P.O. Box 1655, Colorado 

Springs, Colorado 80901, U.S.A. 

Petroleum Information/Dwights LLC, 1999a [includes data current as of December, 1998], 

PetroROM Production Data: Englewood, Colo., Petroleum Information/Dwights LLC; database 

now available from IHS Energy Group, 15 Inverness Way East, D205, Englewood, Colorado 

80112, U.S.A. 

Petroleum Information/Dwights LLC, 1999b [includes data current as of December, 1998], Well 

History Control System: Englewood, Colo., Petroleum Information/Dwights LLC; database now 

available from IHS Energy Group, 15 Inverness Way East, D205, Englewood, Colorado 80112, 

U.S.A. 

A5-8
Appendix 6 

EIA Proved Reserves Estimation

 and Field Boundary Construction 

APPENDIX 6 

ENERGY INFORMATION ADMINISTRATION 

PROVED RESERVES ESTIMATION AND FIELD BOUNDARY 

CONSTRUCTION 

Summary 

The EPCA task of the Reserves and Production Division, Office of Oil and Gas, Energy 

Information Administration, was to ascertain the relationship of proved reserves of crude oil, 

natural gas and natural gas liquids to Federal lands located in selected geologic basins of the 

Rocky Mountain region. This involved attribution of reported and imputed proved reserves to 

individual fields, development of field boundaries, and relation of the field boundaries and the 

associated proved reserves estimates to Federal lands. The primary results are presented in multilayered GIS format accompanied by metadata compliant with the Federal Geographic Data 

Committee Metadata Standard. 

Five sources of data were assembled and conditioned for the project: 

1) The 2001 Form EIA-23 Reserves Survey, which was the source for the bulk of 

proved reserves 

2) The commercially vended IHS Energy Group (IHS) Production Data set, which 

provided field and reservoir names and 2001 production 

3) The IHS Well History Data set, which provided the bulk of the individual well 

locations 

4) Relevant State web sites that were consulted to augment the IHS data as respects 

field and reservoir names, locations, and status 

5) Federal lands boundary data, provided by the Department of the Interior 

Several steps were involved in the data assembly and conditioning phase: 

1) Identifying study area wells, reservoirs, and fields 

2) Editing and renaming of reservoir and field names to make them consistent from 

source to source 

3) Identification and standardization of well types 

4) Exploration of alternative methods for determining appropriate well buffer sizes 

5) Testing of alternative methods for the rendering of field boundary polygons 

6) Merging of the IHS Production data, the IHS Well History data and the Form 

EIA-23 survey data 

To compare the fields and their reserves to Federal lands it was necessary to construct a boundary 

for each field. Placement of appropriate buffers around individual wells, followed by their union, 

was relied on to create reasonable field boundaries. Buffer size was based on well spacing as 

determined from measurements of the latitude and longitude of an individual well's spud point 

relative to those of neighboring wells within the same reservoir. Rules were developed to 

determine on the basis of these measurements which standard well spacing should be used for 

each reservoir, as well as to handle exceptional cases. Field boundary polygons were generated 

using ESRI’s ArcGIS Version 8.2 software using the standard well spacing-based buffers 

assigned to each reservoir. A Visual Basic application was written to automate this process. The 

software performed these main steps: 

A6-1
Appendix 6 

EIA Proved Reserves Estimation 

and Field Boundary Construction 

1) Selection of all wells and buffer distances with a specific field

2) Creation of a buffer around each well in the field using the assigned "buffer distance"

3) Unioning of the buffers in each field to dissolve inner boundaries of overlapping

buffers 

4) Outputting of a boundary polygon, sometimes more than one polygon, for each 

individual field 

5) Areal comparison the field boundary polygons to the Federal lands polygons resulting 

in output of the Federal lands fraction of the total field area 

Proved reserves estimates submitted on the 2001 Form EIA-23 survey were used in the proved 

reserves estimation process as-reported. For those fields in which only some of the operators 

reported on Form EIA-23, the weighted average reserves-to-production ratio of those which 

reported was multiplied by the production of non-reporting operators to impute the latter's proved 

reserves. To impute proved reserves for those fields in which no operator had reported on Form 

EIA-23, regression equations were developed from the reported observations that were used to 

estimate proved reserves for these typically small fields. The portion of proved reserves 

associated with Federal lands within the field was then computed using the Federal lands fraction 

and each field was assigned to a proved reserves size class sufficiently narrow to be useful for 

EPCA purposes while at the same time broad enough to ensure confidentiality of each Form EIA23 respondent's proprietary proved reserves estimates. 

For the entire study area, proved Federal lands liquid reserves (crude oil plus condensate) were 

estimated to be 53.6 percent of total proved reserves; individual basins ranged from 0.0 to 68.9 

percent. Similarly, for the entire study area, proved Federal lands gas reserves were estimated to 

be 60.1 percent of total proved reserves; individual basins ranged from 0.0 to 79.4 percent. Also 

for the entire study area, Federal lands proved BOE reserves were estimated to be 59.5 percent of 

total proved reserves; individual basins ranged from 0.0 to 78.6 percent. 

The Study Areas 

The basins targeted in this initial EPCA study and the States and counties pertinent to them are 

listed in Table A6-1. Final Federal lands boundaries for the study areas were received from the 

USGS on July 17, 2002. All wells in the listed States and counties for which location information 

(in the form of latitude and longitude coordinates) was available were plotted along with the 

study area boundaries. Wells not located within the study area boundaries were then discarded. 

Table A6-1: Targeted Basins and Their State and County Affiliations 

Montana Overthrust Belt

 State Counties 

Montana Beaverhead, Broadwater, Cascade, Deer Lodge, Flathead, Gallatin, 

Glacier, 

Granite, Jefferson, Lake, Lewis & Clark, Lincoln, Madison, Meagher, 

Mineral, Missoula, Park, Pondera, Powell, Ravalli, Sanders, Silver 

Bow, Teton 

A6-2 
Appendix 6 

EIA Proved Reserves Estimation

 and Field Boundary Construction 

Paradox-San Juan Basin

 State Counties 

Colorado Archuleta, Dolores, La Plata, Mesa (part), Montezuma, Montrose 

(part), San Miguel, 

San Juan 

New Mexico Cibola, McKinley, Rio Arriba, San Juan, Sandoval 

Utah Emery (part), Garfield, Grand (part), Iron, Kane, Piute, San Juan, 

Sevier (part), Washington, Wayne 

Powder River Basin

 State Counties 

Montana Bighorn, Carter, Custer, Powder River, Rosebud, Treasure 

Nebraska Sioux 

South Dakota Custer, Fall River 

Wyoming Campbell, Converse, Crook, Johnson, Natrona, Niobrara, Sheridan, 

Weston 

Greater Green River (SW Wyoming) Basin

 State Counties 

Colorado Eagle, Garfield (part), Moffat (part), Rio Blanco (part), Routt 

Utah Daggett, Summit 

Wyoming Carbon, Fremont, Lincoln, Sublette, Sweetwater, Teton, Uinta 

Uinta-Piceance Basin

 State Counties 

Colorado Delta, Garfield (part), Gunnison, Mesa (part), Moffat (part), Montrose 

(part), Ouray, 

Pitkin, Rio Blanco (part) 

Utah Carbon, Duchesne, Emery (part), Grand (part), Juab, Sanpete, Sevier (part), Uintah, 

Utah, Wasatch 

Note: “(part)” indicates that more than one basin applies to a county 

The Data Sources 

Five principal sources of data were used for this study: 

a. The 2001 Form EIA-23 Survey files which contain field production and proved reserves

estimates as reported by the largest operators.

b. IHS Production CD’s which contain crude oil, AD gas, NA and condensate production

at the well (for gas) or lease (for oil) level.

c. IHS Well History CD’s which contain well history records. The well data include well

spud point location (latitude and longitude thereof generated by Tobin International,

Ltd.), field names, producing formation(s), and well type at the time of completion.

d. Many of the Rocky Mountain States have official websites that provided supporting data 

on locations and field names. Links to the websites used in this study are listed below.

A6-3
Appendix 6 

EIA Proved Reserves Estimation 

and Field Boundary Construction 

Colorado web mapper http://cogccweb.state.co.us/maps/ 

Colorado data http://oil-gas.state.co.us/ 

Montana web mapper http://www.bogc.dnrc.state.mt.us/website/mtcbm/webmapper_intro.htm 

Montana data http://bogc.dnrc.state.mt.us/jdpIntro.htm 

New Mexico web mapper http://geoinfo.nmt.edu/resources/petroleum/poolmaps.html 

New Mexico data http://octane.nmt.edu/data/,http://www.emnrd.state.nm.us/ocd/data.htm 

South Dakota maps (not interactive) http://www.sdgs.usd.edu/digitalpubmaps/testholewells 

testholewellsmapne.html 

South Dakota data http://www.state.sd.us/denr/DES/Mining/Oil&Gas/producti.htm 

Utah web mapper http://dogm.nr.state.ut.us/oilgas/MAP%20SEARCH/map_search.htm 

Utah data http://dogm.nr.state.ut.us/oilgas/qref_Find_data.htm 

e. Federal lands boundary data provided by the Department of the Interior. 

Limitations Imposed by the Available Data Sources 

A variety of shortcomings and flaws in the presently available data sources impose unavoidable 

limitations either on what can be done or on the achievable level of accuracy. Chief among these 

are: 

1) Aside from the Form EIA-23 survey data base, which contains standardized field 

name spellings and corresponding standardized field codes, field and reservoir names 

are all too frequently non-standard as respects content and/or spelling. This makes 

accurate automated -- often even manual -- matching of field and well records across 

data sources difficult at best and sometimes impossible. While the standardized field 

codes are assigned and supported by EIA, most field names and their spellings are 

assigned by State agencies. Much of the problem is rooted in the fact that, over the 

past two-plus decades, many of the producing States have trimmed the resources 

devoted to this task, with the result that the extant staffs are overburdened and large 

backlogs exist. When reporting well or production information for a field on which 

the State has not yet acted, a field’s operator is free to use any name it fancies, 

spelled however it wishes. 

An additional causative factor was the demise of the American Association of 

Petroleum Geologists' Committee on Statistics of Drilling, which for many years 

performed an essential initial and subsequently recursive quality control function 

relative to the Nation's well statistics and field and reservoir identities. Staffed by 

experienced industry personnel whose services were “voluntarily” contributed by the 

firm they worked for, the Committee was disbanded in the wake of the 1986 oil price 

collapse. Its files were turned over to the American Petroleum Institute (API) which 

for many years attempted to maintain and update them absent the "in-the-field" 

quality control that the Committee had provided. When API’s budget also 

diminished, and the last of the API staff familiar with the well files retired, they were 

transferred to two competing commercial data vendors for continued maintenance 

and updating. Both recipient firms are now subsumed in IHS. 

2) Well misclassification is a perennial problem. For the most part, it is caused by 

insufficient recursive quality control. For example, a new well may initially be 

classified as a wildcat well, which by definition has discovered a new field. 

Subsequent drilling of extension wells in this or an adjacent field may, over time 

(sometimes over decades) connect the two adjacent fields, at which point both fields 

will shift to the field name of the earliest discovered of the two. This and similar 

sorts of things happen frequently, but that fact often never filters backward in time, 

A6-4
Appendix 6 

EIA Proved Reserves Estimation

 and Field Boundary Construction 

i.e., in this case to re-classification of the wildcat well type to extension or even 

development status. 

3) With the notable exception of fields located on the Federal Outer Continental Shelf, 

the Federal government does not as a rule have access to subsurface data other than 

the usually incomplete well-specific data resident in the IHS Well History file. We 

do not have access to field operators’ seismic data and interpretations, nor to their 

surface and subsurface geologic maps, nor to their well logs. Such information has 

historically been treated as proprietary and private in the United States. In the 

context of the EPCA study, lack of this information limits what can be done as 

respects the construction of field boundaries to a purely geometric approach based on 

the buffering of well locations around their surface spud points. 

The resultant field boundaries are therefore approximations, the accuracy of which in 

the absence of adequate subsurface information depends to a greater or lesser extent, 

from case-to-case, on the professional judgment of RPDs experienced petroleum 

geologists and engineers as to what appears to be a reasonable boundary. 

Collectively the field boundaries provided here are likely to be of sufficient 

accuracy for policy formulation as respects access to Federal onshore lands. But 

in specific instances, they may not be good enough for the application of policy and 

regulation. 

General Process Overview 

Figure A6-1 is a flow chart of the major steps followed in estimation of field-level proved 

reserves (on the left-hand side) and the construction of field boundaries (on the right-hand side), 

as well as their merger into the final principal reserves product. The following discussion 

provides details for each of the indicated steps. 

A6-5
Field-Operator

Appendix 6 

EIA Proved Reserves Estimation 

and Field Boundary Construction 

Figure A6-1 Proved Reserves Estimation and Field Outline Development 

Process Flows 

EIA-23 Survey Data State Data from WWW IHS Production Data IHS Well History Data 

Merge by API Well #

 Condition Data

Merge By Field and Sum Wells to Field and Conditioned IHS Data

Operator within Field Operator within Field

Calculate Well Buffers by

Merged Survey-IHS Reservoir within Field

Reserves Assignment Well Buffers by Reservoir within Field

 And Imputation 

Buffer wells and Union to

 Generate Field Polygons 

Sum to Field Level

Intersect with Federal Land 

Fields with Reserves Field Outlines with Percent Federal Land and

 Federal Land Coverage Outline within Field

Merge by Field 

Assign Fields to Reserve Size Classes 

Field Outlines with Federal Reserves Size Class 

A6-6 
Appendix 6 

EIA Proved Reserves Estimation

 and Field Boundary Construction 

Data Conditioning 

Merging of the IHS Production and Well History files 

This step combined the annual production data with well location and well type. The API well 

number, present in both files, was the key to this merging process. Figure A6-2 shows the 

percentage of wells that were matched by API number and the percentage that was unique to the 

Well History file. 

Figure A6-2 Matching of Wells by API Number and Source 

Well

 History

 Data 

Production

 Data 

Records in Well data only

 All Data 

Well Data Production Well Data 

In the IHS Well History file and the IHS Production file 82.25%

 In the IHS Well History file only 17.75%

 Total 100.00%

IHS Well History records that did not match with IHS Production records were most often dry 

holes, injection, or storage wells. These were discarded. To create valid field boundaries, only 

oil and gas wells were retained, whether or not they had recorded 2001 production data. The 

following rules and procedures were developed and used to merge the files: 

a. Preparation of spud point location information (well latitude and longitude at the 

surface) 

The location information in the IHS Well History file is Tobin’s most accurate 

coordinates. They were therefore used when available. If location information was not 

present in the Well History file, the location information in the Production file was used. 

If location information was not available in either dataset, the well record was deleted 

from the data used for field boundary construction. These well records were, however, 

retained for merger with the Form EIA-23 data base because, even absent a location, 

these wells could at the field level be rolled up with other wells in the same field for 

which location information was available.

A6-7
Appendix 6 

EIA Proved Reserves Estimation 

and Field Boundary Construction 

b. Editing/Renaming of Fields and Reservoirs 

As previously noted, variations in field and reservoir names and spellings are common in 

the commercially-vended data files and some State sources. Names were altered when 

necessary to make them as consistent as possible. The problem of missing names also 

had to be addressed, often through contact with State personnel. To achieve better field 

boundaries it was assumed that the buffers created for wells should be calculated on a 

reservoir level and that the field boundary would then be constructed by unioning of the 

reservoirs in the field. 

Names carried on the IHS Production file were used when they were available. 

Otherwise, names from the IHS Well History file were used. 

If a record appeared not to have a legitimate field name, (e.g., ‘UNDESIGNATED’, 

‘UNKNOWN’, ‘WILDCAT’), a concatenation of Basin and State was used to replace it 

(e.g. new field names like “PRB_WY”, “UPB_CO”, “UPB_UT”, etc, were created). 

When records appeared not to have a legitimate reservoir name, (e.g., ‘UNKNOWN’, 

‘UNKNWN’, ‘WILDCAT’), “UNNAMED” was used as reservoir name. 

If a reservoir name was abbreviated, the full reservoir name was assigned. If a reservoir 

name was augmented by a layer/zone/horizon modifier (e.g. “Dakota A,” “Dakota B”) 

the modifier was removed (e.g. all were changed to “Dakota”). Most records did not 

have horizon information available so the zone name was used instead as the best 

available data for reservoir naming. 

Some field names were changed based on information obtained from State websites and 

conversations with State agency personnel. The CBM reservoir and field names were 

especially affected by the State agencies. For example, as development progressed in 

Wyoming’s Powder River Basin (PRB) the State initially classified wells into fields using 

a system originally designed for application to conventional reservoirs and fields. The 

result was usually related to pre-existing field names for deeper conventional oil and gas 

reservoirs. In apparent belated recognition that the CBM in the PRB is really resident in 

a whole coal field, they now assign all CBM wells in the basin to the field “PRB,” i.e., 

the wells are assigned to a field comprising the entirety of a producing coal seam (see 

http://wogcc.state.wy.us/coalres.cfm for a list). After conversations with geologist Gary 

Strong of the Wyoming Oil & Gas Conservation Commission, it was decided that for this 

study all wells in the PRB with a producing coal reservoir name or which had the IHS 

attribute “CBM” = yes would be reclassified into the field “PRB_CBM_WY”. An 

exception to this procedure was the Fort Union formation where, per Strong, most of the 

current wells are CBM completions but a few are conventional oil or gas. Thus Fort 

Union wells were not put into “PRB_CBM_WY” unless “CBM” = yes or the word 

“coal” was in present in the reservoir name. 

c. Identification of Well Types for Later Buffering 

Deciding which wells to include in the buffering process was critically important to the 

construction of field boundaries. All wells with type = oil or gas in the IHS Production 

file were kept. If wells were identified as a dry hole, a CO2 producer, or an injection well 

in the IHS Production file, but were identified as an oil or gas well in IHS Well History 

file, the well type was reclassified to oil or gas. If well records came from IHS Well 

History file only, the many well types were grouped into four classes: Oil, Gas, Dry hole, 

A6-8
Appendix 6 

EIA Proved Reserves Estimation

 and Field Boundary Construction 

and Injection. Following final assignment of the well type, only the oil and gas wells 

were retained for input to the buffering process. 

The Construction of Well Buffers 

The procedure used to generate well buffers consisted of several development and application 

steps: 

a. Testing of Alternative Procedures

Creation of oil and gas field boundaries was accomplished using ArcGIS. The first 

method tested was the convex polygon method, which draws a minimum-bounding 

polygon around a group of wells such that all of the outer angles are convex. While 

this technique is fine for a structurally simple field, such an oval-shaped anticline with 

a uniform hydrocarbon-water contact, many fields have an irregular boundary owing to 

stratigraphic and/or structural complexity. For these fields a convex hull overestimates 

productive acreage. 

The second method tested was the triangular irregular network (TIN). A TIN 

represents a set of points (wells) as a set of contiguous, non-overlapping triangles. The 

triangles are then unioned into one polygon for the entire field. This method has the 

advantage of being able to include a z-value such as thickness or perforated interval. 

Its disadvantage is that the maximum edge length for triangle construction must be 

specified field-by-field, which made it too laborious for a project with almost 2000 

fields boundaries to build. 

The method ultimately used for construction of the field boundaries was to buffer each 

well in a field with a circle. The radius of the circle was determined by analysis of the 

spacing pattern for each reservoir in the field. The buffer polygons were then unioned 

into a single field boundary polygon record for each field. Given the time constraints 

on the EPCA project, this method was selected because it most effectively utilizes the 

different reservoir spacing patterns within a field and is relatively easy to perform on a 

large data set. 

Figure A6-3 shows Bell Creek Field with the field boundaries created using each of the three 

methods described above. The convex hull boundary shown does not include all of the field's 

wells, only those in the Muddy reservoir. 

A6-9
Appendix 6 

EIA Proved Reserves Estimation 

and Field Boundary Construction 

Figure A6-3 Bell Creek Field, Powder River Basin, Wyoming, Showing Alternative Field 

Boundaries 

b. Determination of Nominal Well Spacing and the Assignment of Buffer Radii 

An analysis of the distances between wells in a reservoir, calculated from their spud point 

locations, was used to assign a standard well spacing unit to each reservoir. Nearest 

neighbor inter-well separation distances were calculated separately for oil wells and gas 

wells. The upper and lower bounds of observed spacing ranges are shown in the two lefthand columns of Table A6-2. The corresponding nominal standard well spacings (a 

geometric distribution) and buffer radii are shown in the two right-hand columns. The 

75th percentile (P75) of the observed inter-well distance distribution was taken to be the 

observed inter-well distance. This statistic was selected because, as judged by the 

Reserves and Production Division of the EIA (RPD) project team, it yielded the best 

match to nominal spacings in an extensive set of map trials. If the P75 distance fell 

within the corresponding interval shown in the two left-hand columns of the table then 

corresponding nominal spacing was selected and its buffer size was initially assigned to 

every well in the reservoir. 

A6-10
Appendix 6 

EIA Proved Reserves Estimation

 and Field Boundary Construction 

Inter-Well Distance 

Nominal 

Spacing Unit 

(acres) 

Corresponding 

Buffer Radius 

(feet) 

Lower Bound 

(feet) 

Upper Bound 

(feet) 

0 277 1.25 233 

277 392 2.5 330 

392 555 5 467 

555 785 10 660 

785 1110 20 933 

1110 1570 40 1320 

1570 2220 80 1867 

2220 3140 160 2640 

3140 4440 320 3734 

> 4440 640 5280 

Table A6-2. Interwell Distance Ranges, Nominal Standard Well Spacings, and Buffer Radii 

c. Well Buffer Construction Rules 

Rules for the assignment of buffers were created to handle reservoirs that did not, for 

whatever reason, readily yield a nominal spacing. They are based on well types and 

well counts. 

1. For oil reservoirs, the maximum spacing allowed was 160 acres, i.e. a buffer 

radius of 2,640 feet (exceptions are listed below). 

2. If the reservoir had between 1 and 10 oil wells or the reservoir name was 

‘UNNAMED’, a spacing of 160 acres was assigned. 

3. For gas reservoirs the maximum spacing allowed was 640 acres, i.e. a buffer 

radius of 5,280 feet (for exceptions, see below). 

4. If the reservoir had only 1 gas well or the reservoir was named 

‘UNNAMED’, a spacing of 640 acres was assigned. 

5. For coal bed methane wells a spacing of 160 acres was assigned, i.e. a buffer 

radius of 2,640 feet (exceptions are listed below). 

6. If the oil well count /(oil well count + gas well count) ratio was less than or 

equal to 5% and if the oil well spacing was greater than the gas well spacing, 

the oil well spacing was set to the gas well spacing; otherwise, the original 

oil well spacing was retained. 

A6-11
Appendix 6 

EIA Proved Reserves Estimation 

and Field Boundary Construction 

7. If the ratio of gas well count/(oil well count + gas well count) was less than 

or equal to 5%, the gas well spacing was set to the oil well spacing for the 

field or reservoir; otherwise, the original gas well spacing was retained. 

d. Exceptions to These Rules 

Altamont-Bluebell-Cedar Rim Field (three names for different parts of same physical 

field), Uinta Basin, Utah:

The P75 calculated buffer radius for the main Green River and Wasatch reservoirs 

ranges from 320-640 acres. Because production is oil, the default maximum 160-

acre buffer was used initially, resulting in numerous isolated polygon rings. 

According to Montgomery and Morgan (1998, American Association of Petroleum 

Geologists (AAPG) Bulletin 82:6:1113-1132), the major portion of this field was 

developed on 320-ac spacing for the fractured Green River and Wasatch reservoirs. 

Thus, an exception was made in this field and 320-acre spacing was assumed for the 

buffers (3,734 feet buffer radius). 

Puerto Chiquito West Field, San Juan Basin, New Mexico: 

The P75 calculated buffer radius for the main Mancos reservoir is 640 acres. 

Because the production is oil, the default maximum 160-acre buffer was used 

initially, resulting in numerous isolated polygon rings. Spacing rules for the field 

specify 320-acre units due to the excellent reservoir communication in the fractured 

Mancos, according to Gorham et al (1979, AAPG Bulletin 63:4:598-607. Thus, 320-

acre spacing was assumed for buffer construction (3,734 feet buffer radius). 

Blanco Field, San Juan Basin, New Mexico:

This field ranks third within the study area as respects total number of wells. It has 

8,669 wells, of which 8,498 are Mesa Verde Formation gas completions. The P75 

calculated buffer distance of 2130 feet for the Mesa Verde falls in the uppermost 

range of 1570'-2220' for 80-acre units. At that default spacing, the resultant product 

shows numerous small gaps between the buffers. The largest fields (in numbers of 

wells and reserves) such as Blanco are so much larger than the average field that they 

warrant making of an exception if the default buffer size does not appear to be 

appropriate. Therefore, 160-acre spacing was assumed (2,640 feet buffer radius). 

Fruitland Coal Reservoir, Basin Field, San Juan Basin, New Mexico:

The default radius of 160 acres was overridden on the basis of results of consultations 

with individuals familiar with the field. 320 acre spacing was assigned, i.e., the 

buffer radius is 3,734 feet. 

The Construction of Field Boundaries 

A SAS file containing the oil and gas well data labeled with field name attribute "Field" and 

reservoir name attribute "Reservoir" was imported into ArcGIS as a dBase (.dbf) file. The wells 

were then plotted and converted to a geodatabase feature class. The coordinate system used was 

geographic, decimal degrees, NAD27. 

A6-12
Appendix 6 

EIA Proved Reserves Estimation

 and Field Boundary Construction 

Visual Basic for Applications (VBA) code was written within ArcGIS to provide an automated 

procedure for creation of polygonal field boundaries from buffered wells. The principal steps 

performed were: 

Select the "field name" attribute and “buffer distance” attribute from the well file 

Select all wells with the first "field name" encountered 

Create a buffer around each selected well using "buffer distance" 

Union the buffers 

Dissolve the barriers between overlapping buffers 

Iteratively perform the above steps for each unique "field name” 

Output a polygon feature class with one polygon (often consisting of multiple 

polygon rings) for each field 

Convert to a shapefile 

Calculation of the Federal Lands Fraction within a Field's Boundary 

The Federal land ownership coverages provided by the Department of the Interior (one coverage 

per basin) were utilized. A definition query of "Minerals" = 'Fed' was used to exclude private and 

state land within the coverages. An automated procedure was developed to calculate the fraction 

of federal land and acres of federal land within each oil and gas field polygon. It: 

Intersected the federal land coverages with the field polygons 

Populated two columns in the field boundary polygon table: “FractionFedLand” 

and “Fed_Acres.” 

In the process of calculating the fraction of federal land in the PRB, a “non-simple geometry” 

error was encountered. The only way to work around this was to eliminate some of the very 

small slivers of non-federal land in the PRB coverage. While such slivers are present in all five 

federal land coverages, they only caused problems in the PRB. These are likely not real gaps in 

federal ownership. Rather, they are most probably the result of merging land parcels from 

different sources and/or with different projections. The ELIMINATE command was used to 

merge narrow slivers of non-federal land smaller that 0.5 acres into adjacent federal land 

polygons. The resultant coverage was visually checked against the original to insure that no nonsliver land parcels were eliminated. After this was done, the calculation proceeded without error. 

Review and Quality Control of the Resulting Maps 

An additional part of the VBA routine not included in the above list of steps automated the 

construction of field boundary maps for quality checking purposes. The maps displayed the wells 

in the field and the field boundary polygon. They also showed selected field attributes such as 

State, basin, and percent Federal land. 

To quality control the resultant buffers at a more detailed level, boundaries were also constructed 

at the reservoir level to determine whether the buffer sizes appeared to be appropriate in fields 

that had multiple reservoirs. Numerous fields were checked in this fashion to verify that the 

buffering rules produced a reasonable field boundary. 

The final field-level buffers and fraction of federal land calculations were checked by inspection 

of approximately 150 field maps which covered all fields that had more than 300 wells or more 

than 500,000 barrels-of-oil equivalent proved reserves per the 2001 Form EIA-23 survey. 

A6-13
Appendix 6 

EIA Proved Reserves Estimation 

and Field Boundary Construction 

Figure A6-4 provides an example of the quality control maps. 

Figure A6-4 Osage Field, Powder River Basin, Wyoming, Showing Buffers by Reservoir (top) 

and the Field Boundary Resulting from their Union (bottom) 

A6-14
Appendix 6 

EIA Proved Reserves Estimation

 and Field Boundary Construction 

Field-Level Proved Reserves Estimation 

The conditioned IHS well history and production data were summed to the field/operator level 

and then merged with the by-field proved reserves estimates reported on Form EIA-23 by the 

largest operators. 

Of the 753 field/operator combinations, only 40 (about 5%) could not be matched to the IHS data. 

Since they could not be matched, they were not mappable owing to lack of location information; 

their relationship to federal lands is unknown. The portion of total proved reserves contributed by 

these unmatched fields was very small -- about 1 percent. 

Of the 713 field/operator combinations that matched with the IHS data, 398 (about 56%) had all 

operators in the field reporting. The proved reserves estimates submitted for these fields were 

used as-reported. 

Of the 713 field/operator combinations that matched with the IHS data, 315 (about 44%) had part 

of their proved reserves reported by the surveyed operators. The remainder of these fields’ 

proved reserves was estimated by RPD. Imputation of proved reserves was accomplished by 

assigning the weighted average reserves-to-production ratio of the reporting operators to the nonreporting operators. The non-reporting operators' production volumes, taken from the IHS data, 

were multiplied by this ratio to impute proved reserves for the non-reported portion of these 

fields. 

Proved reserves imputation was also necessary for the remaining 542 fields that had recorded 

2001 production, but whose operators were not required to submit Form EIA-23. Although these 

fields constitute a sizeable fraction of the total fields in the study areas, their proved reserves are 

only a small portion of total proved reserves, less than 4%. Predictive regression equations were 

developed to estimate the proved reserves of these fields, as follows: 

a. Development of Regression Equations 

The proved reserves estimates and corresponding production data reported on the 

2001 Form EIA-23 were used to develop least squares regression equations 

quantitatively descriptive of the relationship between two. The equations were then 

used to impute proved reserves for the 542 fields whose operators were not required 

to complete a Form EIA-23, based on their IHS production data. 

Four equations were developed using SAS statistical software, one each for oil, associateddissolved gas, nonassociated gas, and condensate. The form of the equations is: 

loge (Proved Reserves) = a + b loge (Production) 

The resulting parameters, the number of proved reserves and production pairs each is based on 

(n), and the goodness of fit statistics (r2

) are provided in Table A6-3. 

A6-15
Appendix 6 

EIA Proved Reserves Estimation 

and Field Boundary Construction 

Product

Crude Oil

Associated-Dissolved Gas

Nonassociated Gas

Condensate

n a b r

2 

460 1.4725 1.0924 0.90 

208 1.6646 1.0237 0.93 

672 1.6559 1.0687 0.84 

294 1.9140 1.0030 0.73 

Table A6-3 Regression Equations for the Estimation of Non-Reported Reserves 

b. Assignment and Imputation of Proved Reserves 

When operators reported both production and proved reserves on Form EIA-23, the 

reported volumes were used. When one or more operators reported for a field but 

one or more other operators did not report, a weighted average reserves to production 

ratio was calculated for the reporting operators and multiplied by the missing 

operators' IHS production to estimate their proved reserves. When a field had no 

reporting operators, the regression equations shown above were used to impute 

reserves based on the IHS production data for the field. The final step was to sum the 

reported and imputed proved reserves to obtain the total proved reserves estimate for 

the field. 

Crude oil proved reserves were then summed with proved condensate reserves to 

yield proved liquid reserves. Similarly, proved associated-dissolved gas reserves and 

proved nonassociated gas reserves were summed to yield total proved gas reserves. 

Last, a gas-to-oil ratio of 6000 cubic feet per barrel was used to convert proved gas 

reserves to their oil equivalent, which was then summed with proved liquid reserves 

to yield proved barrel-of-oil-equivalent reserves. 

c. Reserves Classification 

In order to sufficiently protect the proprietary proved reserves data submitted to EIA, 

each field was placed into a reserves class, by product, per the following 

classification scheme: 

Class Number Proved Liquid Reserves 

0 Zero reserves (i.e., no recorded 2001 production) 

1 Greater than zero but less than 10 Mbbl liquid 

2 Greater than 10 but less than 100 Mbbl liquid 

3 Greater than 100 but less than 1000 Mbbl liquid 

4 Greater than 1000 but less than 10000 Mbbl liquid 

5 Greater than 10000 Mbbl liquid 

Class Number Proved Gas Reserves 

0 Zero reserves (i.e., no recorded 2001 production) 

1 Greater than zero but less than 10 MMcf gas 

A6-16
Appendix 6 

EIA Proved Reserves Estimation

 and Field Boundary Construction 

4 Greater than 10 but less than 100 MMcf gas 

5 Greater than 100 but less than 1000 MMcf gas 

4 Greater than 1000 but less than 10000 MMcf gas 

5 Greater than 10000 but less than 100000 MMcf gas 

6 Greater than 100000 MMcf gas.

 Class Number Proved BOE Reserves 

0 Zero reserves (i.e., no recorded 2001 production) 

1 Greater than zero but less than 10 MBOE 

2 Greater than 10 but less than 100 MBOE 

3 Greater than 100 but less than 1000 MBOE 

4 Greater than 1000 but less than 10000 MBOE 

5 Greater than 10000 but less than 100000 MBOE 

6 Greater than 100000 MBOE 

Note: M=1,000; MM=1,000,000; bbl=barrel; cf=cubic feet 

Merging of Proved Reserves Classes with Field Boundaries and Fraction of Federal Land 

A GIS file was then produced that contains the intersection of the Federal land coverages with the 

field boundaries. Owing to the existence of multiple federal land parcels within each field 

boundary, the resultant boundary polygons were then dissolved on the attribute "field" to union 

the data into one polygon record per field. A table with the reserve classes by field (range 0 to 6) 

and the field name was then joined to the dBase file associated with the field boundary shapefile. 

The latter was then converted to coverage format and thence to interchange file format (.e00). 

Summary of Results 

GIS is clearly the information conveyance method of choice where both analysis of Federal lands 

policy and regulations and their application are concerned. The primary proved reserves result is 

therefore a GIS layer containing field boundary polygons attributed with field name and a proved 

reserves size class for each field product. Unfortunately, none of that detailed information can be 

usefully conveyed on a piece of paper this size. You have to use a GIS workstation to view it and 

a wide-format printer to print it at a size where detail can be distinguished. Therefore, in lieu of 

such a close look at the reserves results, basin-by-basin summary statistics are provided in Table 

A6-4. 

A6-17
Appendix 6 

EIA Proved Reserves Estimation 

and Field Boundary Construction 

Basin 

Number 

of 

Fields 

Total 

Liquid 

Reserves 

(Mbbl) 

Federal 

Land 

Liquid 

Reserves 

Percent Total 

Gas 

Reserves 

(MMcf) 

Federal 

Land 

Gas 

Reserves 

Percent Total 

BOE 

Reserves 

(Mbbl) 

Federal 

Land 

BOE 

Reserves 

Percent 

Paradox-San Juan 250 174,193 53,103 30.5 20,653,622 11,033,357 53.4 3,616,464 1,891,996 52.3 

Uinta-Piceance 180 254,329 142,495 56.0 7,181,669 3,779,755 52.6 1,451,274 772,454 53.2 

Greater Green River 281 177,362 122,234 68.9 12,703,038 10,081,667 79.4 2,294,535 1,802,512 78.6 

Powder River 543 193,456 110,783 57.3 2,398,604 927,738 38.7 593,223 265,406 44.7 

Montana Thrust Belt 1 1 0 0.0 0 0 0.0 1 0 0.0 

Total 1,255 799,341 428,616 53.6 42,936,933 25,822,517 60.1 7,955,497 4,732,368 59.5 

Table A6-4 Summary of 2001 Federal Lands Proved Reserves by Study Area 

Another notable result involves the hypothesis that: 

1) on-average, and 

2) owing to the existence of stipulations and other impediments to drilling on Federal 

lands beyond those customarily associated with private leases, 

Even within the boundaries of the study area's producing fields, the well density would be lower 

on the Federal lands than on the non-Federal lands. 

The well density on Federal lands within study area's fields was found to be 103.5 acres per well, 

or 6.19 wells per square mile (640 acres). The well density on the non-Federal lands within the 

study area's fields was found to be 96.5 acres per well, or 6.63 wells per square mile. This result 

supports the hypothesis. 

A6-18
Appendix 7 

GIS Methodology 

APPENDIX 7 

GIS METHODOLOGY 

Following are further descriptions of how Federal lands were categorized into the ten categories referred 

to in table 2c in Section 2.4.1 and a detailed description of the GIS methodology used. 

Table A7-1 shows the “No Leasing Pending Land Use Planning or NEPA Compliance (NLA/LUP)” 

jurisdictions within the EPCA inventory area. 

FS or BLM jurisdiction 

Ashley NF 

Big Horn NF 

Bitterroot NF 

Bridger-Teton NF 

Custer NF 

Dillon, MT BLM Field Office 

Dixie NF 

Fish Lake NF 

Flathead NF 

Gallatin NF 

Gunnison, CO BLM Field Office 

Kootenai NF 

Lewis and Clark NF 

Lolo NF 

Rio Grande NF 

Routt-Medicine Bow 

Wasatch-Cache NF 

Uinta NF 

Comments 

Northern unit only 

Areas east of of Highway 191 

Western portion only 

Medicine Bow portion only 

Unmapped western portions only 

Table A7-1 Jurisdictions Classified as NLA/LUP 

Table A7-2 shows how agency jurisdictions were used to categorize lands for this inventory. 

A7-1 
Appendix 7 

GIS Methodology 

Federal Land Management Categorization Level 

Bureau of Land Management BLM Subject to stipulations 

Bureau of Reclamation BREC Subject to stipulations 

Department of Agriculture* USDA No Leasing (Administrative), general category (NLA)* 3. 

Department of Defense** DOD No Leasing (Administrative), general category (NLA)** 3. 

Federal Split Estate SPLIT Subject to stipulations 

Fish and Wildlife Service FWS No Leasing (Administrative), general category (NLA) 3. 

Forest Service FS Subject to stipulations 

National Park Service NPS No Leasing (Statutory/Executive Order), (NLS) 1. 

Federal Land Use Designations 

Inventoried Roadless Areas IRA Subject to stipulations 

National Conservation Areas NCA No Leasing (Statutory/Executive Order), (NLS) 1. 

National Monuments NM No Leasing (Statutory/Executive Order), (NLS) 1. 

National Recreation Areas NRA No Leasing (Statutory/Executive Order), (NLS) 1. 

National Wildlife Refuges NWR No Leasing (Statutory/Executive Order), (NLS) 1. 

Special Designated Areas SDA No Leasing (Statutory/Executive Order), (NLS) 1. 

Wilderness Areas WILD No Leasing (Statutory/Executive Order), (NLS) 1. 

Wilderness Reinventory Areas WRA No Leasing (Administrative), general category (NLA) for offices 3. 

listed in next table; otherwise subject to stipulations 

Wilderness Study Areas WSA No Leasing (Statutory/Executive Order), (NLS) 1. 

* Ft. Keo Agricultural Experimental Station, MT, only

** Except for the Naval Petroleum Reserve, Casper Field Office, which is subject to stipulations

Table A7-2 Federal Land Categorization 

Jurisdiction 

Ashley NF 

Farmington NM BLM Field Office 

Glenwood Springs CO BLM Field Office 

Grand Junction CO BLM Field Office 

Grand Mesa /Uncompahgre /Gunnison NF 

Gunnison CO BLM Field Office 

Kemmerer WY BLM Field Office 

Lander WY BLM Field Office 

Little Snake CO BLM Field Office 

Manti La Sal NF 

Moab CO BLM Field Office 

Monticello CO BLM Field Office 

Pinedale WY BLM Field Office 

Price UT BLM Field Office 

Rawlins WY BLM Field Office 

Rock Springs WY BLM Field Office 

Routt-Medicine Bow NF 

Uinta NF 

Uncompahgre CO BLM Field Office 

Vernal UT BLM Field Office 

White River CO BLM Field Office 

White River NF 

Comments 

Uinta/Piceance Study Area 

GGR Study Area 

Uinta/Piceance Study Area 

Table A7-3 Jurisdictions with Wilderness Reinventory Areas (WRAs) 

Classified as NLA 

A7-2 
Appendix 7 

GIS Methodology 

Jurisdiction Comments 

Cedar City UT BLM Field Office Spring Creek Canyon only 

Durango CO BLM Field Office 

Glenwood Springs CO BLM Field Office 

Grand Junction CO BLM Field Office 

Grand Mesa /Uncompahgre /Gunnison NF 

Little Snake CO BLM Field Office 

Price UT BLM Field Office 

Uncompahgre CO BLM Field Office 

Vernal UT BLM Field Office 

Table A7-4 Jurisdictions with Citizen's Proposal Areas (CPAs) Classified as NLA 

National Forests affected by the Roadless Areas Conservation Rule (36 CFR 294) were considered 

available for leasing in this inventory. The rationale for this decision is that as of the date of this report, 

implementation of the Roadless Rule has been enjoined by the Federal District Court of Idaho.12 

However, if current litigation upholds this rule, it could highly restrict or make inaccessible 

approximately 6.1 million acres within the study areas. For this reason, leases offered and/or issued in 

areas covered by the Roadless Rule have attached to them a Notice to Lessees informing them that all or 

part of the lease is within an area covered by this rule. 

Citizens’ Proposal Areas (CPAs) located on Federal land, primarily managed by the BLM in Utah and 

Colorado, are places which have been proposed as wilderness by environmental groups. The treatment of 

CPAs differs by state and by office (Table A7-4). In Utah, offices that have CPAs individually determine 

their treatment with respect to oil and gas leasing. In Colorado, the CPAs are generally considered NLA 

unless the area under consideration has been explicitly examined as part of a particular BLM Field 

Office's planning process.13 

GIS files were available to define most of the access categories; however, for the NLA/LUP category, 

they had to be created. In these situations, the administrative boundary (such as a National Forest) was 

extracted from the surface ownership data and the resultant polygon was then attributed as NLA/LUP. 

For example in Figure A7-1, the national forests in the western Uinta Basin are shown in green. The 

beige area represents the Ashley National Forest (northern unit), which is categorized as NLA/LUP. 

12 Idaho vs. Dombeck CV01-11-N-EJL (D.C.Id. 2001 Kootenai Tribe of Idaho et al. vs. Dombeck). Colorado and

Alaska have joined Idaho; Utah has also filed.

13 BLM, Colorado State Office, Instruction Memorandum No. CO-97-044.

A7-3
Appendix 7 

GIS Methodology 

Figure A7-1 Creation of NLA/LUP Shapefiles 

Stipulation Exceptions 

Sometimes exceptions to stipulations are granted for valid reasons. For example, for a crucial elk winter 

range timing limitation, an exception may be granted if seasonal conditions (e.g., an early spring and 

snowmelt) are such that the elk have moved out of and are not using the general areas during a particular 

year. Because records of exceptions to lease stipulations were not available, BLM and USDA-FS field 

personnel were asked to determine, based on their experience, which lease stipulations were granted 

exceptions for drilling and how often. The exception factors thus determined are shown by jurisdiction in 

Table A7-6. 

Lease stipulations, particularly timing limitations, can overlap. Where exception factors overlap, the 

cumulative effect is calculated by multiplying the overlapping factors (from Table A7-6). This 

calculation implicitly assumes that exceptions for multiple stipulations would likely not be obtained for a 

given area. For example, cumulative effects of excepted stipulations for the Greater Green River study 

area are computed as shown in Table A7-7. The application of these exception factors is described below 

in the section titled “Analytical Modeling of Federal Lands and Resources.” 

A7-4
Appendix 7 

GIS Methodology 

Jurisdiction Exceptions to stipulations Comments Big Game Winter Range Raptors Sage Grouse Steep slopes Bald Eagle Winter Roost Calving and Fawning Antelope Fawning City of Rifle Water-shed Sensitive Resources Soils, Watershed Sedimentation (roads) 

Buffalo WY BLM Field Office 25% 25% 

Carson NF 10% 10% 

Casper UT BLM Field Office 25% 25% 

Durango CO BLM Field Office 50% 50% 50% 

Glenwood Springs CO BLM Field Office 100% Uinta/Piceance Study Area 

Glenwood Springs CO BLM Field Office 20% 30% 20% GGR Study Area 

Grand Junction CO BLM Field Office 70% 15% 30% 

Kemmerer WY BLM Field Office 30% 50% 50% 

Lander WY BLM Field Office 20% 30% 20% 

Little Snake CO BLM Field Office 20% 30% 20% 

Manti La Sal NF 50% 80% 

Miles City MT BLM Field Office 50% 50% 10% 

Missoula MT BLM Field Office 20% 20% 15% 

Moab UT BLM Field Office 70% 70% 70% 

Pinedale WY BLM Field Office 50% 40% 40% 

Rawlins WY BLM Field Office 20% 30% 20% 

Rock Springs WY BLM Field Office 30% 25% 20% 

Routt-Medicine Bow NF 20% 30% 20% GGR Study Area 

Uncompahgre CO BLM Field Office 50% 50% 50% Paradox/San Juan Study Area 

Uncompahgre CO BLM Field Office 10% 10% Uinta/Piceance Study Area 

White River CO BLM Field Office 80% 25% Uinta/Piceance Study Area 

White River CO BLM Field Office 20% 30% 20% GGR Study Area 

White River NF 50% 

Table A7-6 Stipulation Exception Factors List by USDA-FS and BLM Office 

Stipulation Exception Factor (EF) 

Big Game 20% 

Sage Grouse 20% 

Raptors 30% 

Big Game and Sage Grouse 4% 

Big Game/Raptors 6% 

Sage Grouse/Raptors 6% 

Big Game, Sage Grouse and Raptors 1.2% 

Table A7-7 Exception Factors (GGR Study Area) 

Treatment of NSO Areas 

Directional drilling (or "extended drilling”) is a technology that can be employed to reach subsurface 

targets not located directly underneath the drill site. Resources beyond a certain "extended drilling zone" 

(EDZ) are assumed not to be technically recoverable (Figure A7-2). While it is true that directional 

drilling horizontally out to distances of 5 or 6 miles is possible in production settings such as Alaska, this 

type of drilling is impractical for exploration in the Western basins. 

A7-5
Appendix 7 

GIS Methodology 

Directional drilling for exploratory purposes occurs in Western basins, but it is much more limited in 

scope. As in the case of stipulation exceptions, BLM and USDA-FS field personnel were interviewed to 

determine the practicable width of the EDZ. The width of the EDZ is partially a function of the depth to 

the drilling objective—generally the deeper the objective, the larger the EDZ. The EDZ distances 

supplied by the offices and used in the EPCA inventory are shown in Table A7-8. 

Extended Drilling Zone 

Drilling 

Location 

Unreachable 

Subsurface 

Target 

Stream 

Reachable 

Subsurface 

Target 

Not to Scale 

Extended Drilling Zone

Drilling

Location

Unreachable

Subsurface

Target

Stream 

Reachable

Subsurface

Target

Not to Scale

NSO

Figure A7-2. Extended Drilling Zone 

The effect of the inclusion of the EDZs in the analysis was to remove an area of land from the perimeters 

of NSO polygons. The width of this area removed via GIS processing is determined by Federal 

jurisdiction (Table A7-8). The area removed then defaults to the access category that would otherwise 

apply in the absence of the NSO stipulation. The net effect is that the underlying resource is no longer 

considered inaccessible even though the surface above it cannot be occupied by drilling equipment. 

A7-6
Appendix 7 

GIS Methodology 

Jurisdiction EDZ (miles) 

Albuquerque NM BLM Field Office 0.25 

Ashley NF 0.25 

Beavehead-Deerlodge NF 0.50 

Black Hills NF 0.25 

Buffalo WY BLM Field Office 0.25 

Buffalo Gap NG 0.13 

Butte MT BLM Field Office 0.25 

Carson NF 0.25 

Casper WY BLM Field Office 0.25 

Cedar City UT BLM Field Office 0.00 

Cibola NF 0.25 

Durango CO BLM Field Office 0.00 

Durango CO BLM Field Office 0.50 

Farmington NM BLM Field Office 0.25 

Glenwood Springs CO BLM Field Office 0.25 

Grand Junction CO BLM Field Office 0.25 

Grand Mesa /Uncompahgre /Gunnison NF 0.00 

Grand Mesa /Uncompahgre /Gunnison NF 0.25 

Gunnison CO BLM Field Office 0.25 

Helena NF 0.25 

Kanab UT BLM Field Office 0.00 

Kemmerer WY BLM Field Office 0.25 

Lander WY BLM Field Office 0.25 

Lewis and Clark NF 0.25 

Lewistown MT BLM Field Office 0.25 

Little Snake CO BLM Field Office 0.25 

Manti La Sal NF 0.25 

Manti La Sal NF 0.50 

Miles City MT BLM Field Office 0.25 

Missoula MT BLM Field Office 0.50 

Moab UT BLM Field Office 0.25 

Monticello UT BLM Field Office 0.25 

New Castle WY BLM Field Office 0.00 

Oglala NG 0.13 

Pinedale WY BLM Field Office 0.25 

Price UT BLM Field Office 0.00 

Price UT BLM Field Office 0.25 

Rawlins WY BLM Field Office 0.25 

Richfield UT BLM Field Office 0.00 

Richfield UT BLM Field Office 0.25 

Rock Springs WY BLM Field Office 0.25 

Routt-Medicine Bow NF 0.25 

Salt Lake UT BLM Field Office 0.25 

Santa Fe NF 0.25 

South Dakota BLM Field Office 0.25 

St. George UT BLM Field Office 0.00 

Thunder Basin NG 0.25 

Uinta NF 0.25 

Uncompahgre CO BLM Field Office 0.50 

Uncompahgre CO BLM Field Office 0.25 

Vernal UT BLM Field Office 0.00 

White River CO BLM Field Office 0.25 

White River NF 0.25 

Comments 

San Juan Basin portion 

Paradox Basin portion 

Paradox/San Juan Study Area 

Uinta/Piceance Study Area 

Eastern portions only 

Paradox/San Juan Study Area 

Uinta/Piceance Study Area 

Paradox/San Juan Study Area 

Uinta/Piceance Study Area 

Paradox/San Juan Study Area 

Uinta/Piceance Study Area 

Paradox/San Juan Study Area 

Uinta/Piceance Study Area 

Table A7-8 Extended Drilling Zones by Jurisdiction 

A7-7 
Appendix 7 

GIS Methodology 

Figure A7-3 shows an example from the Uinta/Piceance Basin. Areas shown in red represent a 1/4-mile 

extended drilling zone removed from the NSO areas. Areas shown in beige represent the remaining NSO 

stipulations. Note that many small features are completely removed from the NSO theme by use of the 

EDZ. Similarly, linear NSO features less than 1/2 mile wide, such as trails, are removed as well. 

Figure A7-3 Removal of the Extended Drilling Zone from NSO Areas 

Analytical Modeling of Federal Lands and Resources 

The analytical goal of the EPCA inventory is to calculate the area of Federal lands (including non-Federal 

lands overlying federally owned oil and gas estate [split estate]) in each access category in the hierarchy 

and the volume of oil and gas resources underlying the Federal lands in each access category, while at the 

same time accounting for stipulation exceptions and the accessibility of the EDZ. 

One of the primary goals for the development of the categorization was to achieve geographic 

independence for a given parcel of land subject to overlapping stipulations (hence, the use of the 

categorization hierarchy where that parcel of land would be subject to only one category). The following 

discussion illustrates the application of the land access categorization for an area of multiple stipulations 

from southern Wyoming near the Colorado state border (Greater Green River Study Area), where a raptor 

nest, sage grouse nest, and mule deer winter range define an access category. These types of stipulations 

are among the most common found in the study areas. 

Figure A7-4 shows a selected point where the stipulations overlap and the resultant categorization is 

“Timing Limitation Stipulation (TLS) 6-9” according to the access categorization hierarchy. Figure A7-5 

shows the land categorization before processing, but with the application of all stipulations in the area. 

Note that the core nest of the sage grouse stipulation (shown is blue), which cannot be occupied, is 

A7-8
Sage 

Grouse 

Stipulated 

Area

Standard 

Lease Term 

Area

Raptor Nests

Mule 

Deer 

Winter 

Range

Non-Federal Area

Sage

Grouse

Stipulated

Area

Raptor Nests

Mule

Deer

Winter

Sage

Grouse

Nest

Standard

Lease

Term Area

Appendix 7 

GIS Methodology 

considered "no surface occupancy” area (NSO). The remaining area is under various timing limitations 

(colored in shades of red) or under standard lease terms (in green). 

VLG0075.PPT

Sage 

Grouse 

Stipulated 

Area 

Standard 

Lease Term 

Area 

Raptor Nests 

Mule 

Deer 

Winter 

Range 

Non-Federal Area 

Figure A7-4 Display of Overlapping Timing Limitations (GGR Study Area) 

VLG0075.PPT

Standard 

Lease 

Term Area 

Sage Area Grouse 

Sage 

Grouse 

Stipulated 

Nest 

Raptor Nests 

Mule 

Deer 

Winter 

Range

Figure A7-5 Display of Land Access Categorization (GGR Study Area) A7-9 
Raptor Nests

Sage Grouse 

Nest 

Removed in 

the Analysis

Sage 

Grouse 

Stipulated 

Area

Mule 

Deer 

Winter 

Range

Standard 

Lease 

Term Area

Appendix 7 

GIS Methodology 

Next, Figure A7-6 shows the effect where the EDZ is applied to NSO areas. Note that use of the EDZ 

makes the sage grouse nest transparent to the categorization. Using a GIS-driven model developed for the 

project, all stipulations were similarly subjected to the categorization hierarchy and are presented in an 

interactive map, termed LACE (land access categorization, executable), accompanying this report. 

Additionally, to account for stipulation exceptions in the analysis, the GIS-driven model determined the 

effects due to the presence or absence of the stipulations by selectively removing excepted stipulations in 

the computer. This is illustrated by Figure A7-7, which shows this for the example for the Greater Green 

River Study Area, where the raptor stipulation has been removed. Note that, in the absence of an 

excepted stipulation, the analysis defaults to the underlying stipulation or standard lease terms, as 

appropriate. 

VLG0075.PPT

Standard 

Lease 

Term Area 

Sage Grouse 

Nest 

Removed in 

the Analysis 

Sage 

Grouse 

Stipulated 

Area 

Raptor Nests 

Mule 

Deer 

Winter 

Range 

Figure A7-6 Display of Land Access Categorization with Extended 

Drilling Zone Applied (GGR Study Area) 

If, for example, raptor stipulations are excepted 30 percent of the time, then, for an area represented by 

the raptor polygon (where raptor stipulations do not overlap other excepted stipulations), 30 percent from 

the contribution are represented by conditions where the raptor stipulation is not present and 70 percent 

(=1 minus 30 percent) of the contribution comes from the conditions represented where the raptor 

stipulation is present. The total is calculated accordingly for all combinations of the exception factors 

within a given office jurisdiction (see Table A7-8) or where combinations of these exceptions exist (see 

Table:A7-9). 

A7-10
Exempted Raptor 

Nests Removed in 

the Analysis

Sage 

Grouse 

Stipulated 

Area

Mule 

Deer 

Winter 

Range

Standard 

Lease 

Term Area

Appendix 7 

GIS Methodology 

VLG0075.PPT

Standard 

Lease 

Term Area 

Sage 

Grouse 

Stipulated 

Area 

Exempted Raptor 

Nests Removed in 

the Analysis 

Mule 

Deer 

Winter 

Range 

Figure A7-7 Display of Land Access Categorization with Extended Drilling Zone Applied and with Raptor 

Stipulation Removed (GGR Study Area) 

Access categorization of the Federal lands and resources was determined in aggregate in the studies based 

upon discrete examination of individual GIS polygons using the following equation: 

FLorRs = 3((1-EF) * FLorRs (EDZ) + (EF * FLorRs (EDZ w/ Excepted))) 

Where FlorRs = Federal Lands or Resources 

EF = Exception Factor (e.g., see Table 7.4.1.3b) 

FLorRs (EDZ) = FLorRs determined using the Extended Drilling Zone 

FLorRs (EDZ w/ Excepted) = FLorRs determined using the EDZ plus removal of stipulations 

for which exceptions are granted 

This equation allocates Federal lands and resources to access categories in the analysis based on use of 

the extended drilling zone and depending upon the presence or absence of excepted stipulations. As the 

excepted stipulations are removed to estimate Federal lands and resources, the model is set so as to 

default to the underlying stipulation category in the hierarchy. 

This process results in the generation of hundreds of thousands of individual GIS polygons for the study 

areas, each with unique Federal lands and resources access characteristics. These data are then summed 

and reported by access category and Federal management agency. For oil and gas resources, 

A7-11
Appendix 7 

GIS Methodology 

categorization is provided by specific resource type (Section 7.2.1) .

14 By definition of their producibility, 

proved reserves are categorized as standard lease terms in the EPCA inventory. 

14 An Excel spreadsheet showing the results for Federal lands and resources by BLM office jurisdiction for each 

study area in the EPCA inventory is provided on the CD-ROMs accompanying this report. 

A7-12 
1986 

Appendix 8 

Land Management and Resource Documents 

Used in the EPCA Inventory 

APPENDIX 8 

LAND MANAGEMENT AND RESOURCE DOCUMENTS 

USED IN THE EPCA INVENTORY 

Approved RMP for Public Lands Administered by the BLM Buffalo Field Office, 2000 

Beaverhead National Forest EIS, 1996 

Black Hills National Forest Land and RMP, 1991 

Book Cliffs Proposed RMP/ Final Environmental Impact Statement (FEIS), 1984 

Book Cliffs Record of Decision (ROD) & RPS, 1985 

Bridger-Teton National Forest Plan 

Bureau of Reclamation Special Stipulations, Billings Montana Office 

Carson Nation Forest Plan, 1982 

Cedar Beaver Garfield antimony Approved Resource Management Plan (ARMP)/ROD and RPS, 

Cibola National Forest Plan 

Colorado State BLM Statewide Stipulations 

Department of Energy Federal Lands Analysis Natural Gas Assessment, Southern Wyoming and 

Northwestern Colorado, 1999 

Diamond Mtn Recreation Area (RA) ARMP/ROD, 1994 

Diamond Mtn RA PRMP/FEIS, 1993 

Farmington Oil and Gas Leasing Amendment, 1991 

Final EIS for the Newcastle Resource Management Plan, 1999 

Garnet RMP, 1986 

Glenwood Springs Resource Area Plan Amendment, 1999 

Grand Mesa/Uncompahgre/Gunnison National Forest Forest Plan, 1993 

Grand Resource RMP, 1985 

Grand Staircase Escalante National Monument Management Plan, 1999 

A8-1
Appendix 8 

Land Management and Resource Documents 

Used in the EPCA Inventory 

Headwaters RMP, 1983 

Helena National Forest Forest Plan, 1986 

Henry Mt Management Framework Plan (MFP), 1982 

Kemmerer RMP/ROD, 1986 

Lewis & Clark National Forest Oil and Gas Leasing Final EIS, 1997 

Lopez Project Utah State BLM Statewide Stipulations 

Manti-La Sal Final EIS for Oil and Gas Leasing on Lands Administered by the Manti-La Sal 

National Forest, 1986 

Manti-La Sal Final EIS for Oil and Gas Leasing on Lands Administered by the Manti-La Sal 

National Forest, 1986 

Master Index of Utah BLM Land Use Plans & Amendments on CD, 2001 

Miles City Oil and Gas Amendment, 1994 

Miles City RMP, 1991 

Montana State BLM Standard Stipulations 

Northern Great Plains Final EIS 

Paria Management Framework Plan, 1981 

Parker Mountain MFP, 1982 

Platte River RMP Revised & Updated Decisions, 2001 

Rio Puerco RMP, 1992 

ROD & Approved RMP for Public Lands Administered by the Newcastle Field Office, 2000 

Routt National Forest Oil and Gas Leasing Analysis/FEIS, 1993 

San Juan National Forest Forest Plan, 1983 

San Juan RA ARMP/ROD, 1991 

San Juan/San Miguel RMP 1991 Oil and Gas Amendment 

San Rafel RA ARMP/ROD, 1991 

Santa Fe National Forest Plan 1987, 1996 Amendment 

Shoshone National Forest Final Oil and Gas Leasing EIS/ROD, 1992 

A8-2
Appendix 8 

Land Management and Resource Documents 

Used in the EPCA Inventory 

St. George Office RMP, 1999 

Vermillion Management Framework Plan, 1981 

White River National Forest ROD 

White River Resource Area RMP 

Wyodak Coal Bed Methane Project final EIS, 2000 

Wyodak drainage Coal Bed Methane EA, 2000 

Wyoming St BLM Statewide Stipulations 

Zion Management Framework Plan, 1981 

A8-3