bluuebunny/crossref_metadata_2025 huggingface dataset:
The Use of Computers in Pressure Transient Analysis
Authors: Buhidma I. M. , Chu W. C. , Singh P. K.
Published: December 2007

The use of computers for pressure transient analysis is now a routine practice in the petroleum industry. Several pressure analysis techniques have been developed over the last few years that not only lend themselves to easy implementation on computers but necessitate the use of computers. The combination of the ability to acquire highly sensitive and accurate pressure data and the easy access of these analysis techniques allows the engineer to employ sophisticated methods to analyze the data. This paper presents state-of-the-art computer applications of pressure transient analysis using techniques available in today’s software. Field examples of applications that a typical user would not attempt without a computer are presented. The advantages of these methods over conventional analysis methods are also demonstrated. Applications include pressure derivative, pressure integral, rate superposition, and the use of pseudo functions.

This paper also presents a list of recommended features and attributes of what constitute, in our opinion, a good pressure transient analysis program. It is hoped that the list will provide a standard and serve as a guide to developers of pressure transient analysis packages.
Robust Procedures for Parameter Estimation by Automated Type-Curve Matching
Authors: Carvalho R. S. , Redner R. A. , Thompson L. G. , Reynolds A. C.
Published: December 2007

Type curve analysis of pressure transient data influenced by wellbore storage effects can yield non-unique answers due to similarity in the shapes of the curves. In order to alleviate this problem, several researchers have proposed methods for unbiased parameter estimation using nonlinear regression analysis techniques. Typically, these methods are sensitive to initial guesses for the parameter values; thus, with poor initial estimates, it is possible that the schemes may diverge or converge to wrong answers. The probability of convergence to correct parameter values is further decreased if the data contains outliers; i.e., measured data whose behavior is significantly different from the "average" behavior of the data set.

In this work, we focus on practical methods of applying the nonlinear regression to the analysis of pressure transient data. Our aim is to provide procedures that enhance the probability of obtaining a unique match, and which detect and properly account for the presence of outliers. A new two-step procedure which utilizes the pressure-pressure derivative ratio in the first step, is demonstrated to increase the chances of obtaining a unique fit. Also, we present a new method of applying "robust" parameter estimation (which accounts for data outliers) that uses commonly available algorithms based on least squares (LS) regression. We demonstrate applicability of the proposed methods by analyzing several sets of field data.
Reservoir Characterization, Haygood Limestone (Ferry Lake Anhydrite), Caddo-Pine Island Field, Louisiana
Authors: O’Hearn T. C. , Funk J. J. , Callender C. A. , Pepin G. P.
Published: December 2007

Reservoir characterization of the Haygood Limestone (Ferry Lake Anhydrite, Early Cretaceous) at Caddo-Pine Island field in Caddo Parish, Louisiana, has enhanced the design of a proposed waterflood recovery program. Analyses to evaluate reservoir geology, formation injectivity, porosity types and pore size distributions include conventional core description, thin section petrography, X-ray diffraction, X-ray computed tomography (CT), and petrographic and scanning electron image analysis (PIA and SEM-IA).

The Haygood Limestone is a thin, very fine calcarenite to fine calcirudite (intraclast bioclast packstone to grainstone) which is overlain and underlain by bedded anhydrite. The reservoir interval has an average porosity of 17.0%, an average permeability of 10.89 md and is characterized by a homogeneous pore network with a narrow pore size distribution. The base and the top of the Haygood are characterized by thin nonreservoir zones which effectively enhance the in situ stratigraphic trap. These zones possess decreased porosity and permeability and heterogeneous pore networks with broad pore size distributions.

Porosity types include interparticle, moldic, intraparticle and microporosity. Interparticle and moldic pores are the dominant pore types, and are variably reduced by bladed to equant calcite and blocky anhydrite cements. Microporosity is locally significant, establishing a bimodal pore system and increasing bound (irreducible) water content.
Simulation of Subseismic Faults Using Fractal and Multifractal Geometry
Authors: Belfield W. C.
Published: December 2007

An important problem of reservoir description is the prediction of faults that are not detected by seismic techniques. Such faults can disrupt flow unit continuity or may be potential targets for horizontal drilling. One approach to describing their distribution is stochastic modeling. This paper describes a technique to simulate the number, length, orientation, and spatial distribution of subseismic faults using fractal and multifractal concepts.

The approach exploits the fractal nature of faults to determine their true length distribution. Faults are characterized by a multifractal spectrum rather than just a single fractal dimension. The multifractal distribution of mapped seismic faults forms the basis for the areal allocation of stochastic faults. One use of the stochastic fault simulations is to predict the probability of intersecting a fault as a function of well length.
The Effect of Four Geostatistical Methods on Reservoir Description and Flow Mechanism
Authors: Ghori S. G. , Ouenes Ahmed , Pope G. A. , Sepehrnoori Kamy , Heller J. P.
Published: December 2007

Determination of uncertainty in the description of reservoir properties is an important aspect of enhanced oil recovery projects. This paper compares four geostatistical techniques: simulated annealing method (SAM), source point method (SPM), fast fourier transform method (FFTM), and turning band method (TBM) in the generation of property distribution. The four methods are tested and compared by using an exhaustive minipermeameter permeability measured data set, and a tracer flow experiment on a rock sample. The methods are used in conditional simulation, assuming some known permeability data. The conditioned fields are then used in the simulation of miscible tracer flow through the sample rock and compared with the actual tracer concentration curves. The methods are compared on the basis of 1) spatial distribution and the variograms of the generated fields, 2) global error variance, 3) computational cost of generated fields, 4) effect on flow dynamics, and 5) tracer production curves.

Comparison of the four methods has shown that SAM produces the best fit of the experimental variograms without regard to the type of variogram (e.g., trend, etc.). The FFTM and TBM can utilize many types of theoretical variograms. All four methods can produce anisotropic fields. Although the spatial distribution obtained by SAM preserves the main features of the original data better than the other three methods, the global error variance in SAM is 25% more than in SPM, FFTM, and TBM. When considering computer run time and storage, SPM is the most efficient method, followed by TBM, FFTM, and finally SAM.

Finally, the conditioned permeability fields from these methods are used in the simulation of a miscible tracer flow through the rock sample and compared with the actual tracer output curves. It is observed that a very good fit of the simulated variogram to the experimental ones, will not necessarily give a good production history match. Rather, based upon similarity between the simulated and experimental tracer output concentration histories, the best results were obtained with SPM, then TBM, SAM, and finally FFTM.
Risk Assessment Approach to Offshore Safety: Part A—Norwegian Regulatory Philosophy
Authors: Olstad H. T.
Published: December 2007

The Norwegian Petroleum Directorate (NPD) has since the mid-seventies put increasing emphasis on the use of risk analysis techniques in the industry as one of the tools for enhancing safety in exploration and production activities offshore Norway. This approach now forms a cornerstone for updated offshore safety Regulations. In this paper, background internal control obligations of operators are reviewed along with safety supervisory activities of the NPD. The concepts of safety objectives and acceptance criteria as applied to offshore activities are presented. The subsequent use of risk analysis as a tool to highlight areas requiring further attention is discussed. Finally, the "performance-based" nature of the new detailed regulations in defining safety upgrade actions is also reviewed.
Foamed High-Concentration/High-Volume Mud Acid Stimulations at South Belridge Field
Authors: Dominquez F. E. , Lawson J. B.
Published: December 2007

This paper documents the design process and production response of a successful foamed, high hydrofluoric (HF) acid concentration (10% hydrochloric (HCI) acid/5% HF), high volume (150 gal/ft) mud acid stimulation program performed in 1991 on thermal production wells in the Tulare formation of the South Belridge Field. The recommended program was based on the results of laboratory work on Tulare core and a lookback study of a 1989/1990 mud acid stimulation program. In comparison to the prior stimulation program, the 1991 program gave better results; both the total program success rate and the treatment cost per incremental BOPD improved by a factor of 3.
Optimizing the Quality of High-Density Brines for Maximum Performance and Economic Value
Authors: Foxenberg W. E. , Houchin L. R. , Javora P. H.
Published: December 2007

The benefits derived from the use of solids-free high density (HD) brine completion fluids have been extensively documented. The technology to produce and utilize these HD brines was known for many years before they could be made commercially viable. Their use only became economical in the 1970’s when the technology was developed to recondition and re-use these HD brines until fully consumed. Recently, increased competition and cost cutting pressures have resulted in a reduction in quality standards. As a consequence, some operators have begun specifying new brines only. If this trend continues, the actual cost of these valuable salts and the added cost of disposal would be applied to the suppliers price after a single usage. It is this very situation that prevented operators from utilizing HD brines in the 1950’s and 60s. It was not in their best economic interest then nor is it today.

The central problem seems to be the confusion surrounding minimum standards for reconditioned HD brines. Unfortunately, some service companies and operators alike have begun accepting the removal of suspended solids as the exclusive criteria for brine restoration. While the simple filtration of a completion fluid to some arbitrary level may appear cost effective, unseen inherent problems may compromise the functionality of the fluid, be damaging to the formation, complicate normal rig operations, and contribute to unexpected additional cost.

This paper provides guidelines for restoring used brines to new brine standards by addressing both physical and chemical contaminants. Laboratory procedures and operational guidelines are provided that establish methods for identifying problematic contaminants and simulate the brine specific reclamation techniques and field application requirements. Standards for restoring used brines to new/non-damaging compositions are also provided.
Size-Dependency of Hollow Cylinder Collapse Strength
Authors: van den Hoek P. J. , Kooijman A. P. , Kenter C. J. , Khodaverdian Mohamad , Hyland C. R. , McLennan J. D.
Published: December 2007

This paper presents the results of an experimental study of the size dependency of hollow-cylinder (HC) collapse strength in the absence of inner-hole pressure for tight, brittle sandstones. An earlier study on friable Castlegate outcrop sandstone showed that HC strength falls strongly with increasing sample size in this material, implying that small-scale laboratory HC collapse tests may overestimate borehole stability. The present study, however, revealed a much lower size dependency for tight Berea outcrop sandstone and for tight North Sea sandstone. Examination of the borehole shape after testing suggests that breakouts in larger holes grow by a shear mechanism in Berea sandstone, and by a spelling mechanism in Castlegate sandstone. The results for smaller holes in Berea sandstone are less unequivocal: spelling cannot be excluded here as the mechanism for breakout growth.
Optimum Gravel Sizing for Effective Sand Control
Authors: Oyeneyin M. B. , Peden J. M. , Hosseini Ali , Ren Guowu , Bigno Yann
Published: December 2007

Efficient sand control is dependent on the design of the exclusion system and must take into account a number of formation characteristics and production factors which will affect the eventual well performance. For gravelpacking, the design requires the specification of the size of the commercial gravel to use with the final objective being the achievement of maximum productivity over the production life of the well with effective sand exclusion.

To date, a number of formulae have been suggested for gravel size selection, the most popular being the Saucier formula. However in a large number of gravelpacks, operators have reported fines being produced in large quantities, suggesting ineffective bridging by the gravelpack.

A review of the available gravel sizing formulae show that they may be too general and possibly too simplistic to take full cognisance of the depositional environment of the formation sand, the operational conditions to which the gravelpack is subjected, the reservoir fluid, the gravelpack structure, etc.

A project has been initiated in the Department of Petroleum Engineering at Heriot-Watt University to address the problem of determining the optimum gravel size under a range of different operational conditions. The project has the objective of developing a theoretical approach and modelling technique to predict gravel size and also to evaluate particle-pore bridging phenomena, using a series of rigorously defined experiments.

This paper presents the results of the comprehensive experimental investigations carried out to evaluate the bridging effectiveness of various commercial gravels as a function of different operational conditions including the sand sorting and shape.

The experimental studies were carried out using a purposely-built packed column to evaluate the effects of production rate, fluid type, formation sand and gravel characteristics, absolute and differential pressure on the efficiency of the exclusion treatment.

The bridging efficiency of selected gravels were measured. The experimental data generated formed the data base for developing a semi-empirical bridging efficiency equation which assists in the selection of gravel and the prediction of its bridging effectiveness under specified operational conditions. It also allows the design engineer to conduct a sensitivity analysis of the effectiveness of the chosen gravel to a range of variable conditions.

The paper concludes with a description of the computer package being developed for optimum gravel size selection. This package is expected not only to select the optimum gravel size but also predict the eventual well performance.
Case Histories of New Low-Cost Fluid Isolation Technology
Authors: Littlefield B. A. , Fader P. D. , Surles B. W.
Published: December 2007

Texaco has developed a process to shut off steam and water encroachment in production wells. The process involves placing a stable resin system across the zone to be shut off. The resin leaks off into the formation where it polymerizes to form an impermeable plug. The resin plug is stable to temperatures of 700 °F and inert to normal oil field chemicals. The resin is easy to mix, requiring no specialized equipment. The set time of the resin is controllable at any downhole temperature.

The process was tested in Texaco’s Kern River and San Ardo Fields in 1990 and 1991. Thirty-three wells were treated with the resin. Twenty-six of the wells were production wells suffering from water encroachment. The other wells were treated for steam cutting, casing holes, or injection well leaks. About seventy percent (19) of the production wells showed a significant reduction in water production after treatment. Four wells did not show a reduction because the water encroachment zone is above the zone treated. An effective plug could not be made in the other three wells due to highly desaturated or void spaces in the treated zone.
Membrane Filtration of Seawater for Oil Reservoir Injection
Authors: Seland Aina , Bilstad Torleiv , Mehan Surinder , Bakke Rune
Published: December 2007

In the recovery of hydrocarbons from offshore oil reservoirs seawater injection is frequently applied. Unfortunately, the high concentration of sulphate in the injection water may cause problems such as scaling and souring of oil reservoirs. Membrane filtration using nanomembrane can be applied to reduce the sulphate concentration. Nanomembranes have a high rejection of divalente anions and organic molecules with molecular weight above 200. In the present study the separation performance of a NF70-2570 nanomembrane was evaluated. The removal efficiencies obtained for sulphate, magnesium and calcium were greater than 93 %, 47 % and 37 % respectively. The rejection of monovalent anions such as chloride and bicarbonate were in the order of 10-30 % and 30-60 % respectively. The water flux through the membrane decreased from 36.8 l/m2h to 20 l/m2h at Τ = 26 °C after 64 hours of filtration. The required membrane area for the production of 500 m3/day will be in the order of 1000 - 1400 m2.
Determination of Gas Storage in Devonian Shales With X-Ray-Computed Tomography
Authors: Lu Xiao-Chun , Pepin G. P. , Moss R. M. , Watson A. T.
Published: December 2007

The use of X-ray computed tomography scanning with a dual scan technique to study gas storage and transport in Devonian shales is investigated. Dynamic scanning experiments are performed at various gas pressures. Krypton gas is used as the saturating fluid, and its validity in modeling natural gas storage is discussed. Direct evidence of condensed gas in the Devonian shale is presented, and the role of fractures and shale constituents on gas storage and transport is elucidated.
Natural Gas Vehicle Economic Analysis Model
Authors: Matt S. M.
Published: December 2007

As a natural gas utility in the South Coast Air Quality Basin, Southern California Gas has lost load on its system from increasing restrictions on its industrial customers who are classified as "stationary emitters". Air quality data suggests that the majority of the area’s air pollutants are due to mobile sources, particularly automobiles. The utility sought to develop a new market for its product and to help clean the air in its service territory by giving mobile emitters the opportunity to switch to a cleaner burning fuel, by driving natural gas vehicles (NGVs).

The challenge was to prove to regulators that a market development program, in its infancy of creating both a fueling infrastructure and a market for NGVs could be economic to its ratepayers This paper describes the assumptions and structure of the economic model that the utility used to support the filing for the Program.
Application of Biomarkers to Tracing the Source of Oil-Producing Stratum in Oil-Sand Reservoirs
Authors: Chan M. Y. , Altebaeumer F. J. , Brooks P. W. , Sarioglu G. G.
Published: December 2007

Frequently a lack of definite correlation between the cycle performance and the operating strategy has resulted in optimization difficulties for oilsand reservoirs under the Cyclic Steam Stimulation (CSS) recovery process. Oil itself is the ideal substance to be used as the optimization diagnostic tool among the fluids normally recovered in the course of oil production. The preliminary results from this study clearly illustrate this by utilizing a group of chemical compounds found in oils and bitumens, commonly known as biomarkers, as natural tracers. By determining the degree of biodegradation with depth as suggested by the ratios of certain biomarkers, one can reasonably deduce the originating stratum from which the produced oil has originated at the time of sampling. The hypothesis was developed and proven over a 2½ year period using field pilots of the McMurray Formation of the Athabasca oilsand deposits in Alberta, Canada. The approach has the potential to become a cost effective, routine, short turn around time, reliable, direct and continuous monitoring/diagnostic tool for optimizing CSS as well as other recovery processes.
Heavy-Oil Recovery From Thin Pay Zones by Electromagnetic Heating
Authors: Chakma Amit , Jha K. N.
Published: December 2007

There are many heavy oil reservoirs with thin pay zones (less than 10 m). Conventional thermal recovery methods such as steam injection, are not cost effective for these thin reservoirs due to the excessive heat loss through the overburden. In order to minimize heat losses, it is necessary to have the ability to carry out controlled heating of the pay zone. One such way to introduce heat to the reservoir in a controlled manner is electromagnetic heating. This paper describes laboratory studies on electromagnetic heating of scaled thin heavy oil reservoir pay zone models. Combination of electromagnetic heating and gas injection with horizontal wells was studied.

Higher electromagnetic frequencies provide faster heating rate and can overcome problems associated with discontinuity of the media through which electromagnetic waves must propagate in the reservoir. Heat loss can also be minimized with the use of higher frequencies. For moderately heavy oil reservoirs (less than 1000 mPs.s), it is not necessary to heat the entire pay zone. Heating of the wellbore vicinity is sufficient. Oil recoveries as high as 45% of OIIP (Original Oil in Place) were achieved using electromagnetic heating and gas injection compared to estimated primary recovery rates of less than 5%. The results obtained in this work clearly show that electromagnetic heating provides an effective mean of recovering heavy oil from reservoirs with thin pay zones.
Control of Aromatic Emissions From Glycol Dehydrators
Authors: Choi M. S. , Spisak C. D. , Dodd J. A.
Published: December 2007

Glycol dehydration units utilized in natural gas service have been identified as potential sources of aromatic hydrocarbon emissions into the atmosphere. Depending upon the concentration of aromatic content in the natural gas, large amounts of aromatics may be concentrated in the still overhead water vapor vent. Federal and state regulations have targeted glycol dehydration units for emission control on these carcinogenic compounds. In the near future, some states will levy annual fees to operators who exceed maximum daily discharge limits.

Conoco has developed and applied for a patent on a novel addition to the standard glycol dehydration unit that eliminates the emission of almost all of the aromatics and other hydrocarbons. Hydrocarbons, that are normally vented with the water vapor, are recovered as a condensate product or as regenerator fuel.

A prototype of the Aromatic Recovery Unit (ARU) was successfully placed in operation in November 1990, along with a new 30 MMSCFD glycol dehydration unit. Two additional units are now built and in operation.

This paper describes the design and Conoco’s experience with the prototype Aromatic Recovery Unit.
New Oilfield Applications for Electronic Phase Converters/VSD's
Authors: Elmer W. G. , King J. D.
Published: December 2007

New technology has emerged that has removed many of the limitations for the use of single phase power in oilfield applications. Prior to this technology, capacitive and rotary phase converters have been utilized sparingly due to 1) high inrush currents and 2) poor motor efficiencies. The new technology is a computer controlled solid state power conversion process that eliminates these two problems, and provides additional benefits which include variable speed operation and complete motor protection. Actual oilfield applications of the Solid State Phase Converter (SSPC) for fifteen to fifty horsepower motor driven pumping units, compressors, and positive displacement reciprocating pumps are presented, as are other potential oilfield applications.
Improved Specifications for Manufacturing and Inspection of Sucker Rods
Authors: Ott R. E. , Craig B. D. , Beeson Richard
Published: December 2007

In an effort to reduce well failures, Mobil elected to investigate the reasons for rejection rates in new sucker rods. Independent third party inspections indicated a combined 14.3% rejection rate for new sucker rods from all manufacturers during 1990.

Inspection results indicated a variety of rejects led to these failures. However, each manufacturer also had specific problems that led to the rejection of their rods (e.g. cracked pins, hardness variations, etc.).

This paper presents the finding of laboratory analyses of certain sucker rod defects, as well as the resultant development of a comprehensive sucker rod specification.

Results of comprehensive testing of new sucker rod boxes in accordance with API 11B are also presented and discussed.
Completion Techniques Used in Horizontal Wells Drilled in Shallow Gas Sands in the Gulf of Mexico
Authors: Pardo C. W. , Patrickis A. N.
Published: December 2007

Texaco has completed three horizontal wells in shallow gas sands in the Gulf of Mexico. The producing sands in all these wells have relatively high permeabilities and are unconsolidated. This paper discusses the process used to select the completion hardware, drilling fluids, and completion fluids for these wells. In addition, the completion procedure will be discussed in some detail to illustrate the most significant aspects of the completion process. Finally, production histories of the three wells will be presented to highlight the efficiency of the completion system used in these wells.
The Development of Corrosion Inhibitors With Low-Environmental Toxicity.
Authors: Haslegrave J. A. , Hedges W. M. , Montgomerie H. T. R. , O’Brien T. M.
Published: December 2007

This paper discusses the advantages of corrosion inhibitor treatments for oil production applications. It reviews the current direction of legislation concerning the discharge of oil production chemicals into the environment. It details studies undertaken which show that many existing corrosion inhibitors are toxic towards the marine organisms tested. New chemistries have been developed which display excellent corrosion inhibition properties and which are significantly less toxic.
Results of a Large-Scale Refracture Stimulation Program, Kuparuk River Unit, Alaska
Authors: Pospisil Gordon , Lynch K. W. , Pearson C. M. , Rugen J. A.
Published: December 2007

An aggressive hydraulic fracture stimulation program on previously fractured wells in the Kuparuk River Field has increased production by 50,000 BOPD. The Kuparuk River Field is the second largest producing field in the United States with sixty-five percent of the reserves contained in a 20–100 md permeability sandstone. This paper describes results of a series of design improvements in an ongoing refracture program of oil wells in this moderate permeability formation. Over 185 of the 380 production wells have been refractured during the past five years. Long term production data are presented comparing productivities after the initial stimulations carried out in the early 1980’s to the recent refracture stimulations. A twofold improvement in long term productivity is shown with changes in the treatment design: increased job size, different proppant types (ceramic vs. sand), proppant mesh sizes (10/14 and 12/18 vs. 20/40 and 16/20), and fluid types (gelled water vs. gelled diesel). The average productivity increase from 30 to 60 BOPD/net foot pay provided the economic justification for refracturing some wells a second time. Additionally, wells with high flow potential after initial stimulation have been refractured for substantial increases in oil rate.
Microbially Induced Organic Acid Attack in a Sweet Natural Gas-Gathering System
Authors: Dusseault J. W. , Giovanetto R. H. , Schulz J. H.
Published: December 2007

Microbially produced organic acids in contact with mild steel pipelines can cause an accelerated form of corrosion similar in appearance to a CO2 type of attack. While the two types of attack may appear to be similar in nature their corrosion mitigation methods are different. Chemical corrosion inhibitors which are effective in controlling CO2 attack could be rendered ineffective when treating microbially induced corrosion.

This case study outlines the procedure taken in identifying the internal corrosion mechanisms responsible for the microbially induced corrosion (MIC) failures, selection of the treatment chemicals, monitoring techniques, health and safety aspects of chemical programs and the potential environmental impact of such programs.
Brassey Field Miscible Flood Management Program Features Innovative Tracer Injection
Authors: Anderson J. H. , Laurie R. A. , Loder W. R. , Kennedy Paul
Published: December 2007

An extensive reservoir management program in a hydrocarbon miscible flood has allowed the reservoir team to stay abreast of reservoir performance and to influence ultimate recovery of oil.

A key component of this program, operated by Canadian Hunter Exploration Ltd. at the Brassey miscible flood in British Columbia, included the downhole manufacture of tritiated methane as part of an innovative tracer injection program. Other technical elements in the reservoir management program include frequent pressure surveys, volume monitoring, and compositional analysis.

Teamwork between geologists, reservoir engineers, production/facilities engineers, and field operations staff was absolutely essential to the success of the program.
Reservoir Potential of Thin-Bedded Turbidites: Prospect Tahoe
Authors: White C. D. , Bradburn F. R. , Brown R. L. , Thieme M. A.
Published: December 2007

Geological/Petrophysical modeling, production testing and pressure transient analysis have demonstrated that thin-bedded turbidites can be very productive and have large connected volumes at Prospect Tahoe. This offshore Alabama field (water depth = 1,500 ft) occurs as a northwest-southeast trending turbidite channel/levee complex and is predominantly a gas reservoir with a thin oil rim. There is a relatively large volume of geological and engineering data for this thin-bedded turbidite deposit. In addition to a 3-D seismic survey, there are seven exploratory penetrations (three with whole core), a production test, and PVT analyses from several samples. The hydrocarbon accumulation exhibits a proven hydrocarbon column height in excess of 700 feet over an area greater than 4,000 acres. The reservoir depth at Tahoe is about 10,000 feet subsea, and initial reservoir pressure is about 5,000 psia.

A 100 foot cored interval was completed and production tested, attaining a stabilized rate of 29 MMCFPD for three days. The subsequent five-day downhole shut-in exhibited persistent radial flow, indicating permeability-thickness of 1,700 md-ft and a connected area in excess of 520 acres. In the production test interval, over 1,400 individual beds were identified from whole core. The average sand bed thickness is less than 0.5 inches, and no sand bed exceeds three inches in thickness.

This interdisciplinary study demonstrated that thin-bedded turbidites can be successfully tested, be very productive, and have large connected volumes. This work may have analog application elsewhere.
Relative Permeability at Low Interfacial Tensions
Authors: Ronde Hidde
Published: December 2007

This paper shows that condensate trapping in a retrograde reservoir upon pressure depletion can be described by capillary condensation of a near-critical fluid in hydraulic channels with a permeability in the (tens of) milidarcy range(in contradistinction to capillary condensation for non-near-critical fluids, which occurs in the microdarcy range).

The Porous medium is modeled as a bundle of hydraulic channels, the smaller of which show Bing-hamian condensation, whereas the bigger ones show two-phase flow in a core-annular regime (often called filmflow).

Both phenomena can be explained by the supposition that a Cl-C3 near-critical fluid system goes through a Cahn transition(at an IFTc1-c3 = 0.3mN/m), the latter value being based on pendant drop-measurements on a 2,6-lutidine-water model system and the application of critical scaling principles.

A Cahn transition into a perfect wetting regime is not just a transition from very good wetting to perfect wetting in the capillary sense.This is a consequence of the fact that for near-critical fluids in thermodynamic equilibrium the solid(channel) wall is an essential part of the system that is in thermodynamic equilibrium, leading to a redistribution of phases in the capillaries (now hydraulic channels), whereas the spreading coefficient becomes essentially zero for such a system. When viscous forces are dominant this leads on its turn inside the Pressure-Composion Cl-C3-(Berea) phase envelope to a core-annular ("film-flow") regime for the bigger channels. The smaller ones go upon pressure depletion through a noticeable transition region outside this envelope, (where the effect for the larger ones can be neglected) causing Binghamian condensation. At the Cahn transition inside the envelope relative permeability curves of the Cl-C3(Berea) system straighten shockwise.In the filmflow-regime an Einstein emulsion contribution to relative permeability is clearly identifiable at the saturation extremes leading to asymétrie straightening of the relative permeability curves.
A Pore-Level Scenario for the Development of Mixed Wettability in Oil Reservoirs
Authors: Radke C. J. , Kovscek A. R. , Wong H.
Published: December 2007

Understanding the role of thin films in porous media is vital if wettability is to be elucidated at the pore level. The type and thickness of films coating pore walls determines reservoir wettability and whether or not reservoir rock can be altered from its initial state of wettability. Pore shape, especially pore wall curvature, is an important factor in determining wetting film thickness. Yet, pore shape and the physics of thin wetting films are generally neglected in models of flow in porous rocks. This paper incorporates thin wetting film forces into a collection of capillary tubes model to describe the geological development of so-called mixed-wettability in reservoir rock. Our model emphasizes the remarkable role of thin films.

New pore-level fluid configurations arise that are quite unexpected. For example, efficient water displacement of oil (i.e., low residual oil saturation) characteristic of mixed-wettability porous media comes about due to interconnected oil lenses or rivulets which bridge the walls adjacent to a pore corner.

Predicted residual oil saturations are found to be approximately 35 percent less in mixed-wet rock when compared to completely water-wet rock. Calculated capillary pressure curves mimic those of mixed-wet porous media in the primary drainage, imbibition, and secondary drainage modes. Amott-Harvey indices range from −0.18 to 0.36 also in good agreement with experimental values1,2.
Impact of Section 29 Tax Credits on Unconventional Gas Development and Gas Markets
Authors: Haas M. R. , Goulding A. J.
Published: December 2007

This paper provides some context and an empirical basis to evaluate the historical and potential impact of Section 29 production tax credits on the development and production of unconventional gas resources (UGR). The data, analyses and conclusions reported here are based on studies conducted for government and industry clients over the past two years.

The federal government implemented incentive pricing and Section 29 production tax credits over a decade ago as the principal policy tools to accelerate development of UGR. Given the large expected potential contributions of tight gas, coalbed methane and Devonian shale gas, these incentives were designed to reduce risk and improve project economics of these "high-cost" gas resources.

Despite the fundamental transformation of the gas industry over the past decade, however, the Section 29 credit has not changed in scope or mechanism since its inception in 1980. Critics of the credit allege that, during a time of significant changes in the characterization of the gas resource base, extraction technology effectiveness, gas markets, wellhead prices, and pipeline regulation, the credit has changed from a modest incentive to a major cause of market distortion.

The results of two recent studies are discussed that provide a basis for more rational debate about the merits of eliminating or extending the credit, in either its current or an alternative form. The first study1 addressed allegations that Section 29 credits were responsible for widespread wellhead gas price declines in 1991. After looking at supply, demand, transportation and market behavior for UGR-prone basins during 1991, we conclude that Section 29 credits had only a minor direct affect on wellhead prices.

The second study2 addressed the potential for an alternative configuration of the credit to restore the credit's originally intended impact. Alternative configurations of the credit are offered as a means to adhere to original Congressional intent for the credits, maximize efficiency and equity and minimize costs to the U.S. Treasury. Selection of an optimum credit configuration, however, first requires a clear specification of federal policy objectives.
Sorting Equiprobable Geostatistical Images by Simplified Flow Calculations
Authors: Guerillot D. R. , Morelon I. F.
Published: December 2007

Various geostatistical models have been proposed to generate possible descriptions of the internal structure of heterogeneous reservoirs. For actual reservoir engineering studies, there are practical problems in dealing with large numbers of possible images. This paper proposes an efficient way of sorting the images, accounting for dynamic criteria, allowing a few images to be selected for detailed study.

The method consists in performing simplified reservoir simulations in which the pressure field is held constant in time, rather than being updated at each time step. The pressure field used is calculated by assuming a steady state flow within the reservoir but using the actual boundary conditions (well rates or pressures). The saturation evolution takes into account the multiphase parameters. In this paper, it is shown that these simplified simulations are sufficient to sort the images for a model problem. Here, the criteria used are the breakthrough times and the oil productions.

The advantage of this approach is that significantly less computer time is needed to perform the simplified simulations than the full simulations. This makes it possible to run simplified simulations for many equiprobable images in order to find the extreme behaviors. Some images are then selected for complete simulations. In addition, a working methodology is proposed to determine the number of geostatistical descriptions to be considered.
Developing Gas Reservoir Descriptions Through Multiwell Performance History Matching: Case Histories From Oklahoma’s Anadarko Basin
Authors: Gunter G. W. , Jones J. R.
Published: December 2007

Though history matching of multiwell performance using numerical simulators is a common method of developing reservoir descriptions for oil fields, it is rarely used for gas producing areas. This is appropriate when gas well performance follows conventional theory. When BHP/Z versus cumulative production curves are nonlinear the use of simulation can provide great advantages. This paper illustrates how history matching well by well 72-hour shut-in BHP/Z versus cumulative production plots in a full field numerical simulator is used to develop a complete reservoir description for two gas-producing horizons in Oklahoma’s Anadarko Basin. Such performance data from a 31 well field in the Penn-sylvanian-aged Red Fork sandstone and a 49 well field Mississippian-aged Britt sandstone field were matched using an in-house multiwell gas reservoir simulator. This paper describes the match of the data from the 31 well Red Fork reservoir. This work has significantly improved our understanding of the importance of nonlinear BHP/Z versus versus cumulative production. Using detailed numerical simulation allowed us to account for layering, boundaries, areal property variations, curtailment and offset well effects.

The resulting reservoir description was used with the simulator to identify and/or evaluate infill drilling locations, optimize reserves by exploring various reservoir management options, and to monitor the effects of competitive lease line position to protect reserves. As a direct result of this study, more than 50 BCF of reserves were protected or exploited. The model predictions of future performance are shown to accurately match subsequently measured actual well BHP/Z points for both infill and existing locations. Thus, the reservoir description has proven itself to be a powerful reservoir management tool.
Automatic Waterflood History Matching Using Dimensionless Performance Curves
Authors: Carlson F. M. , Stein M. H.
Published: December 2007

An automatic history matching technique has been developed and tested. A reservoir simulator is used to generate single-layer predictions of performance for volumetric depletion and waterflooding of patterns typically used in a field. To accommodate the effect of a varying initial gas saturation, waterflood predictions are made at several different initial gas saturations at the start of waterflooding. These results are converted in dimensionless form and used to generate multilayer predictions. Nonlinear regression is then used to change the reservoir description until a satisfactory match of historical performance is obtained. While this technique strictly applies only to reservoirs in which crossflow between reservoir layers is negligible and in which vertical heterogeneities dominate areal heterogeneities, it’s more general application is discussed. In addition to being automatic, the technique takes only a few CPU seconds on an IBM 3090 for a typical application.

Comprehensive testing under the assumed developmental conditions is presented. Nonuniqueness aspects of kh and rw are also discussed.

The effects of infill drilling in the history of a reservoir can be accommodated by the technique. Infill drilling is handled by making single-layer waterflood numerical simulations of infill drilling at various levels of pore volumes of injected water prior to infilling.

Testing of the new technique with field data showed good agreement with field data and a multilayer reservoir simulator prediction for the initial stages of waterflooding. It is demonstrated that the infill performance of a reservoir layer with a free gas saturation at the time of infill drilling is somewhat dependent on the gas saturation.
Analysis of Reinfiltration in Fractured Porous Media
Authors: Barkve Tor , Firoozabadi Abbas
Published: December 2007

A scaling of the two-phase, two-dimensional flow in an anisotropic matrix block is proposed. The scaling allows analysis of the reinfiltration process in a matrix block and the study of the influence of gravity, capillarity and matrix block dimensions on reinfiltration and drainage rates. An approximation for the maximum drainage rate of a matrix block without segregation assumption is also derived.

The main conclusion of this paper is that the combination of gravity and capillarity forces generally provides conditions for a pronounced reinfiltration process in fractured porous media.
Effect of Crossflow on Sweep Efficiency in Water/Oil Displacements in Heterogeneous Reservoirs
Authors: Fitzmorris R. E. , Kelsey F. J. , Pande K. K.
Published: December 2007

Fluid crossflow can significantly affect sweep efficiency in heterogeneous reservoirs. The importance of fluid crossflow relative to purely longitudinal convective transport in a two-dimensional setting depends on several factors. Rock properties such as porosity, permeability, the ratio of vertical to horizontal permeability, and length scale of correlation are important factors. Fluid properties such as phase densities, phase viscosities, and interfacial tension are also factors. Coupled rock-fluid properties, for example, wettability, relative permeabilities, and capillary pressure are also factors. In addition to these factors, flow velocity, system dimensions, and boundary conditions also affect sweep efficiency. In this paper we examine the role of capillary forces, in addition to viscous and gravity forces, on sweep efficiency of immiscible displacements in a heterogeneous porous medium. A fully implicit, black oil, reservoir simulation model was used to compute displacement performance in two-dimensional, fine-grid (x-z) cross-sections. The results presented in this paper clearly show the importance of capillary crossflow as a recovery mechanism, in addition to viscous and gravity crossflow, in displacements in heterogeneous reservoirs.
The Impact of Errors in Measurements of Coalbed Methane Reservoir Properties on Well Production Forecasts
Authors: Zuber M. D. , Olszewski A. J.
Published: December 2007

This paper presents the results from two simulation parametric studies of coalbed methane well forecasting techniques. Phase I qualitatively identifies the relative impact of key reservoir properties, and rank orders them. Phase ∏ uses a Monte Carlo simulation approach to quantify the degree of confidence associated with coalbed methane well forecasts for two sets of distributions of key reservoir properties. Results indicate that the range of error associated with the best currently-available reser- voir property measurement techniques significantly impedes the engineer’s ability to accurately forecast production with confidence, and points to the need for improved measurement accuracy for key reservoir properties.
Failure of Chalk During Waterflooding of the Ekofisk Field
Authors: Teufel L. W. , Rhett D. W.
Published: December 2007

A full-field water-injection program for enhanced oil recovery is being conducted in the Ekofisk field, a naturally fractured chalk reservoir in the North Sea. The effect of waterflooding on reservoir behavior has been directly observed in a well that was drilled into an area of the field that has been swept by the waterflood. Measurements of pore pressure, temperature, and in situ stress in this well show that injection of cold seawater at high rates and pressures has locally repressurized the reservoir and reduced reservoir temperature, which in turn has decreased the principal effective stresses. Failure envelopes derived from laboratory compression tests of reservoir chalk indicate that the resultant deviatoric stress is sufficient to cause shear failure of chalk and slippage of fractures. Intense fracturing in repressurized zones of this well observed in logs and core support this conclusion. Large increases in reservoir permeability measured in well tests conducted before and after waterflooding indicate the extensive nature of waterflood-induced fracturing. It is likely that waterflood-induced fracturing has contributed to the very good performance of the Ekofisk waterflood. Waterflood-induced fracturing has increased fracture density and fracture surface area and reduced matrix block dimensions in reservoir chalk, and thereby increased imbibition rates and waterflood sweep efficiency.