GEOLOGICAL SURVEY CIRCULAR 419 

THE DEFINITION OF KNOWN 

GEOLOGIC STRUCTURES OF 

PRODUCING OIL AND GAS FIELDS 

By Emmet A. Finley 

GEOLOGICAL SURVEY CIRCULAR 419 

THE DEFINITION OF KNOWN GEOLOGIC STRUCTURES OF 

PRODUCING OIL AND GAS FIELDS 

By Emmett A. Finley 

This report presents the procedures used by the 

Geological Survey in defining known geologic 

structures for leasing law administration 
United States Department of the Interior 

STEWART L. UDALL, SECRETARY 

Geological Survey 

THOMAS B. NOLAN, DIRECTOR 

REPRINTED 

1960 

1963 

Washington, D. C. 1959 

Free on application to the U.S. Geological Survey, Washington, D. C. 20242 
CONTENTS 

Page 

Introduction............................................. 1 

Interpretation........................................... 1 

Purposes and timing...................................... 5 

Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . 5 

Procedure for structure defined...................... 5 

Procedure for structure undefined.................... 5 

Termination.............................................. 6 

Appeal................................................... 6 

Figure 1. 

2. 

3. 

IUlJSTRATIONS 

Plat of a defined known geologic structure ...• 

Schematic representation of definition 

of known geologic structure ......••......•.. 

Plat showing consolidation of several 

defined areas .......................•....... 

2 

3 

4 

III 

THE DEFINITION OF KNOWN GEOLOGIC STRUCTURES OF 

PRODUCING OIL AND GAS FIELDS 

By Emmett A. Finley 

IN·.rRODUCTION 

On February 25, 1920, the President approved an 

act of the Congress designed to promote the mining of 

coal, phosphate, oil, oil shale, gas, and sodium on 

the public domain. This became the "Mineral leasing 

Act of 1920," and, as amended, has been the basis for 

exploration and development of the named mineral 

commodities on Federal lands. 

In that part of the Act pertaining to oil and gas, 

the following provisions were made: 

anq, 

Sec. 13. That the Secretary of the 

Interior is hereby authorized under such 

necessary and proper rules and regulations 

as he may prescribe, to grant to any applicant qualified under this Act a prospecting 

permit, L-amended to become a noncompetitive 

leas~, which shall give the exclusive 

r~ht for a period not exceeding two years 

Lamended to five yeari7, to prospect for oil or gas upon not to exceed two thousand five 

hundred and sixty acres of land wherein such 

deposits belong to the United States and are 

not within any known geologic structure of 

a producing oil or gas field * * * 

Sec. 17. That all unappropriated 

deposits of oil or gas situated within the 

known geologic structure of a producing oil 

or gas field and the unentered lands containing the same, not subject to preferential 

lease, may be leased by the Secretary of the 

Interior to the highest responsible bidder by 

competitive bidding * * * 

The bases for the determination whereby lands are 

leased noncompetitively or competitively remain 

unchanged as of the present. In an effort to provide 

the public with a better understanding of the procedures employed in differentiating competitive and 

noncompetitive lease acreage, this statement of the 

legal and geologic principles involved in determining "known geologic structures" is published. 

The late John D. Northrop, former Chief, Branch 

of Mineral Classification, Conservation Division, 

Geological Survey, whose Survey career (1911-54) 

spanned the enactment of the Mineral Leasing Act of 

1920 (41 Stat. 437), expressed the opinion in 1941 

that no phrase in the general leasing law of 

February 25, 1920 (now known as the Mineral Leasing 

Act of 1920),has resulted in more speculation as to 

its precise meaning than the phrase "known geologic 

structure of a producing oil or gas field." 

The boundaries of known geologic structures are 

determined by the Director, U.S. Geological Survey, 

by delegated authority from the Secretary of the 

Interior, as prescribed by 43 CFR 192.6. Plats 

(fig. 1) approved by the Director, Geological Survey, 

showing defined boundaries are placed on file in the 

local land offices of the Bureau of Land Management 

and in offices of the Oil and Gas Supervisors and 

Regional Geologists, Conservation Division, Geological 

Survey. 

Known geologic structures are determined on a 

defined and undefined basis. The difference between 

them and procedures followed in determining each is 

discussed below. 

INTERPRETATION 

Through the years the Geological Survey has 

defined the known geologic structure of a producing 

oil or gas field as the trap, whether structural or 

stratigraphic, in which an accumulation of oil or gas 

has taken place. The limits of such structure 

include all acreage that is presumptively productive. 

On April 16, 1936, a decision by the Secretary of the 

Interior (Columbus C. Mabry, 55 I.D. 530) held 

(syllabus): 

The defining of the boundaries of the 

geologic structures of producing oil and 

gas fields, under authority of section 32 

of the leasing Act, is for administrative 

purposes and is not a guaranty of geologic 

character. Accordingly, such boundaries 

are not to be taken as absolutely and 

accurately showing tqe extent in each 

instance of··,the geological structure producing oil or gas, but they may later be 

extended or reduced to accord with the 

facts. 

This premise recognizes that structural traps or 

"known geologic structures" can be more extensive 

than the pools of oil or gas they may contain. Known 

geologic structure definitions are made after evaluation of all controlling factors, and such definitions are made conformable to the dominant structural 

feature involved (fig. 2). 

Where development shows that several fields, 

previously defined individually, actually coalesce 

and are in fact within the limits of the same 

geologic structure, it is administratively feasible 

to consolidate subordinate defined areas into a single area defined as the known geologic structure 

of a single field (fig. 3). 

1 
SALT CREEK FIELD Ts.3~-40-41N. Rs. 78-79W, 6th.PM .. WYOMING 

In accordance with Sec. 192. 6, 

43, C .. F. R. I redefine the known 

geologic structure of the _____ _ 

___ SALT __ CBE.EJ<._ flELD ___ _ Total previously defined __ _ 

Total additionaL __ ~ ___ ~_ 

Acres 

_2_ 4,_2_3_3_ - _ ____ 7_6_Q__ D ~--------------

as indicated hereon, revision_.;__ 

. eff.ecti\Le. .N.a..v.em.b_e_r _2 2~ _1_9_5~t _ 

Total defined ____________ 2~J9_9_~_ 

~A. I\.-'--. 

ACTING 'DIREC -~ o..v.e rnbe.r 22.._,_1~ .5.1_ R.79W. R."!S W. U.S. Geological 

TOR 

Sur vey 4 3 l I I 4 3 \2 I 4 3 12 4 3j 2 i I 4 3 2 I 4 ::--r- I 4 ~~ ~l!.)~ 4 '. 1: I 4 !3 _2 I 4 3J2 I 4 3j_Z I 

' b ~-' f-.~- 5 r-s+ T4-r- -r--, -f-.~- ,..-f-~-1- r-R-•- ~ r-~- ·t r-i- 1- -~-3- -- r---1-- 6 I -+- r-r--+--j T 7 I 7 I --r-- T I I I I 2 I --i-8- -~-r- -·6 -li - -1:2 I 

2 . I 9- -+ ·~ ' ,•, -~ 12__;_ 3 7 3 r-r r i 'f ..- I 4 ""i-+ -+- I 

T I I I I ' I I ' I I I 

,_ •'a- •? .__,~+- '-. 'F- ·~-, I 2 

--·~+- __ ,17 

'--[±.~~ f-~ •• ~- I 

f--H 13-+- 3 I I ',3-r-3 ! I 

4 I 4 ·~ ' ! l ___:_ l_ 

I' I I ~---·+- 1------j--- ---+--+ I ! 2 .'9 r- ~0 f- 21 -~3t rr~; rt f~ f-- -~2 ~2- -~'3 i 1--24 .- 3--H'l+--- -r--'-21-r-r-- 3 14 .. l. -r- -r-f-f- 4 i 'l I I I H---L I 

2 jo r- r--~9 '- 2

1

8 -ds 2 '-+- i1 1- '3 I r--r-~7- ·--f-.25 I 31-30 r--- ~9 f- 1-~8 f- T --l 6 f--- -25 rr4 I I I 1 i I I 

~; I I I I I I 

; ~. r--31

2 r-

·--r3'+-r--- -~5 2 I r-- 3~- -- r-

-r- r-r- H--~6 3 -~1----l------ -- 2----t--- r- 331 t----35 r- -i 36 r- -, r- f-- r-- -- I 

T.41 N. 4'-·- rH T.41N. I I 

T.40N. 14 , .. 4 3 2 I~ 4 3 I~ 4 3 i z T.40N. 

' 6-6-I-f--~- r--r-- j-- 3 ~ (-6- ,_ 1- ~:- t- -L-~- r-----2- I--1-- I I 6 I 

7 7 I I I I L I --- -+- :r--~ I 110 _,. ~~..- 112 12 . 

FH="r- --~- -f-ip ,,, ·~- -r--8 '--r-'-9-r- I-- r,-.-r -- '[ -j- r.tl ----- 4 L l .- I I I-f I 

:H1

a -1:7 -1'6 r-

~~r- = ~~~--~- •'3 ~~'f"' f-i-----117_ ~-~.st i . I 

-r- 1---1-116 r-i 14-j~ f-- 13 

t- I--~ r-- ---+- 4 I I I 4o I I I I 

~t -

~L :--~; ~ I I---' I ' 

:H~ -d4 2 io -f---~1 .!.---- -- r-- ... 213 ~r-- r--3 -·~-- - r-r-~~2 4 

-± I T 4 - r-- I I 4 I . I I 

I -r--l--

:'-31

0 -~~ 2

1

8 r- I I . I 2 d9 .. - -i7 r-- ~27 r- i-26 r---25 r-3 .-H 1----~8 I--f- 2[ 4 l 4 "]__ I I I __l I t _,.. 

314 2 --12 r- 3~ r---~r--- 3~ r-r--31

6 2 3

1

2 ~-r-- f---35 :s -3,1- r-3 311 f-- 1-- -- --- vi' --, ~6 - T.40N. 4 T.40N. I I . 4 I I 

T.39N. "I"' " 3 iE 1!,~3 ~ 4 i 312 I' 4 13 12 I 14 312 3 12 I 4 3 2 I 4 3 2 I 4 15 I z 4 :s 2 I 4 1312 T. 39N. 

~-~ ~- r-r-r-2- r----r-1 6 I 5- r- ~- -r--f-.3 :-r--- ! ' 

7 I 7 I I I I I 

I I I 2 ' r--•p· tr- H-•:2 r-- 31 -i-r----a t'o II-r-- 3-7- f----8 - g- II 1:2 f-- ;;;;, -,- 4 J I I I 4 ! I I I I I 

I I ... ! I I 

2 ·'- f- 'T r-- ·~ --1~ r-f-J .. ,~ h-·~+- 3 rl~ r-r-- 't ~ .~ --f-- 15 - ',4 r--- 13 r- 3-lf .... 4 I I I I I 

L I I 

3f-i~ ~0 ~· 1--t---~2 r-f-- 23 ! ;J, 21 ' 

f- r-r- 1--h ~ol, - ~. -r- ~2 f-- 23 - 2,4+ i 1'1 3 I~ T 4 I I I I i 41. ' .J I I I 

I I I ~~ II : I I I 

~~--~0 - ~9 f-'--f-28 r-----f--27 \- ~6-!----- +25+- 21 30 r-r-- i9 I r-- ia -r-1-~7 r-f--E6 _' 215 r-- I -+- t++ 3 I T 4 i 4 i I I 

I ! I I I 1 

r- ~1'--t--= -:.t-+- -}!-~1- r31

3 f--1-~4 r--+~st- +~6-j--: ~ . .,. I r--f--~ ~4 36 r- - 3 1-r- ·-r- 312 3 -c4 I I I I I l 4 ! I I I I I ! 

R.79W. f R.78W. 

Figure l.••Plat of a defined krlown geolO~ic structure. 
V I ~ #. i J/ : ~ 4/i 1 • 

II I ,'I .- ~j..-'"l i ';/ I ' I 

' 

I' v ::A''! J I ' 

I i _).;""" -~ i 0 I 

I 1 ir1 ; ~1 2 : -, ; ,• 

r-~-+- 34 1·, i35 IJ 3 6-----+------+. 1 .;

1

,:----_:_ 31 I 32J • 3' .. ·~-· t 1 : , 1 3 I 

0

o e-1 1 'v: • • : ·~ I " I ' I 

' ' \ ~ . ! ~ ! :r4 : /~ J / LL 1 

4- 3 2 1\ I 4' 3 I\~ I ~ 3 I 2 'l. I r~ 4 ! 3 I 2/ I 4 Q3 21 I I 4 3 , Z I 

, -.....~ ' I ' : i""'-..m i V ~0 ,_1 ...IIIII J 

' " ,, "J ! ~ 5I II " v I 1---t-'~\--- 3 " ._ ~ "... 1' e 1 6 / ~, '5 -C'l 4 --+___. 

\ ' •'~ '!........ ""'~'... 6 I v"' !,,~ ~o I I 

1\ r\.. " ""- '.. :;-r- ,"1 .. J~" nOD V 

I\ I '\.. I\.. I """-,..., '' I ~ ~ v / 

_____..) . c 

-------- ______ _. 

---

Oi 1- v1ater interface 

Structure contours 

Limit of trap 

Figure 2. --Schematic repres mtation of definition of 

known geologi: structure. 

3 
R.114W. 

~rr~rrrrrrHrHHH-H1~.-L 

t-.-t-H-+++-+-++-1-+-t-++++-t-+-t-t--t---it-'(----;---t.J BIG PINEY- LA BARGE FIELD I 

The Bl G PINEY- LA BARGE FIELD includes areas previously 

within the known geologic structure of the followino fields• 

R.II2W. 

BIG PINEY LA BARGE 

HOGSBACK NORTH LA BARGE 

TIPTOP 

fT ) [I )"' l I • l_lt I 4 S I I 

''.l~•l I ' 1 

R.II4W. R.II3W. 

4 I I I 4 

~ accordon~ewilh Sec.l92.6,43 C. F. R. 

1 define the known geologic structure of 

the BIG PINEY- LA BARGE FIELD 

os indicated hereon, revision& consolidation 

effedive June 24,1958 

I II 10 .- •• It 10~ 

41a]a 41 I I 4 It I 

l • • ; r_t ey " •-

R.II2W. 

i 

--....&..!!..,!--~~ -- ACTING DIRECTOR 

U.S.Geological Survey 

Figure 3.--Plat showing consolidation of several defined areas. 

4 
PURPOSES AND TIMING 

Known geologic structure definitions distinguish 

lands to be leased competitively from lands that are 

subject to noncompetitive leasing, under Section 17 

of the Mineral Leasing Act, as amended. 

Acreage outside a known geologic structure of a 

producing oil and gas field as of the filing date of 

the application, if it is to be leased, is required 

by the Act to be leased to the first qualified 

person making application therefor, without competitive bidding. By instructions of April 23, 1921 

( 41 I. D. 98 ), the Secretary of the Interior stated: 

* * * it is clear that not only equitably but legally, qualified persons who 

filed proper applications for oil and gas 

prospecting permits under the Act of 

February 25, 1920, cannot and should not 

be deprived of their rights if, because of 

delay in action upon the applications so 

filed there intervenes a designation by this 

department of the lands as being·within the 

geological structure of a producing oil or 

gas field occasioned by a discovery of oil 

or gas subsequent to the filing of the 

application in the local land office. 

The prospecting permit applications referred to in 

the quotation are, in effect, the same as current 

applications for aoncompetitive leases. 

Acreage inside a known geological structure is 

subject to disposal by ·competitive bidding. The 

same decision (48 I.D.98) further states: 

* * * prospecting permits cannot be 

allowed within the geological structure of 

a producing oil or gas field, as known and 

existing at and prior to the filing of the 

application for the prospecting permit. 

The filing date of the application for an oil and 

gas lease is the date considered in determining the 

structural status of the lands involved. The 

Department has long held that, if the structure 

underlying the tract of land is actually known to be 

capable of production prior to the date of the 

Department's official announcement, it is the date 

on which facts are available showing the lands to 

be on a producing structure, and not the date of the 

pronouncement to the public, that is determinative 

of rights which depend on whether the land is or is 

not situated within the known geologic structure of 

a producing oil or gas field. See Charles R. Haupt, 

48 I.D. 355 (1921); A. W. Mason, 48 I.D. 213 (1921); 

Sun-Tex Petroleum Company, A-24453 (April 4, 1947). 

PROCEDURE 

Under the authority delegated by 43 CFR 192.6, 

the Director of the Geological Survey determines 

whether lands are or are not within any known 

geologic structure of a producing oil or gas field. 

In making the~e determinations it is recognized that 

the extent and position of any oil and gas accumulation in a known geologic structure, though 

primarily influenced by structure, is also influenced by such factors as stra~igraphy, porosity, 

permeability, and by water and gas pressure in the 

reservoir. Evaluation of the net effect of these 

several facto~s is the result sought by the determination of definition of the known geologic 

structure. These determinations are for all purposes 

required by the provisions of the Mineral Leasing Act 

and the pertinent regulations, particularly, 

l. For appropriate determination of the competitive and noncompetitive leasing provisions under 

5 

Section 17 of the Mineral Leasing Act and 43 CFR 

192.50, of the applicable regulations. 

2. For appropriate application of the two- and 

five-year lease extension provisions under Section 17 

of the Act and 43 CFR 192.120. 

3. For appropriate application of the rental 

waiver provisions under Section 17 of the Act, and 

of the rental provisions of 43 CFR 192.80. 

The Director's determinations require one of two 

procedures, namely, the procedure used in the determination of a geologic structure defined and the 

procedure used in the determination-ofla geologic 

structure undefined. 

Procedure for structure defined 

The geology of the structure is reviewed by a 

board of Survey geologists; their findings are submitted to the Director with a plat depicting the 

lands determined to be within the boundaries of the 

structure. Upon approval by the Director, copies of 

the plat are distributed to appropriate Bureau of 

land Management and Geological Survey offices as 

mentioned in the Introduction. A notice stating that 

the determination has been made, and the effective 

date thereof, is published in the "Notices" section 

of the Federal Register. 

Procedure for structure undefined 

Inasmuch as definitions are required for purposes 

of administration immediately after the initial discovery is made in a new field, or extensions are 

made by outpost drilling, when knowledge both of the 

productive limits of the field and of the physical 

factors which determine such limits is at a minimum, 

known geologic structures undefined are established 

as an administrative expedient for appropriate action 

on the three regulations stated above. 

The essential difference between defined and 

undefined known geologic structure definitions, and 

the reason therefor, is that the formality and detail 

in the defined procedure does not permit the necessary 

day-to-day determinations needed by the Bureau of Land 

Management in current administration of the lease& and 

lease applications. 

Undefined known geologic structures are of two 

types, namely: 

1. An area where discovery necessitates the 

defining of a new productive area, and revisions 

thereof. 

2. An area where development around a previously 

established defined structure warrants an extension 

of the established known geologic structure. 

In connection with undefined geologic structures, 

available information, generally consisting of data 

relating to a single well or a few wells, together 

with available geologic information, is reviewed by 

geologists; and a memorandum is sent to the manager 

of the appropriate land office making a determination 

that certain lands are as of a certain date "on 

structure" or within an undefined addition to a 

previously defined structure. Although the lands 

determined to be on this structure are outlined on a 

work map, no plat is prepared for distribution or for 

filing in the Land Office, and notice of the determination is not published in the Federal Register 

because of its temporary nature. 
Generally, the undefined structure procedure 

applies when there is a discovery on or near a Federal 

lease and an immediate determination is needed for 

guidance of the manager in administering the rental 

and extension provisions of the particular lease or 

leases in the vicinity of the discovery. It is also 

applied in areas where the scope and pace of development are rapid, and where the preparation and publication of a map would be misleading because, in a 

matter of a day or days after publication, or even 

on the date of publication, the boundaries are subject 

to change. 

The undefined structure procedure is also used 

with respect to a field or area where there are but 

one or two tracts of Federal lands, and a determination can be made as to such tracts without the 

necessity of outlining the entire structure. This 

is especially true of the oil-producing States 

(Alabama, Arkansas, Florida, Illinois, Indiana, 

Kentucky, Louisiana, Mississippi, New York, Ohio, 

Pennsylvania, Texas, and West Virginia) where Federal 

acreage holdings are few and generally consist of 

widely scattered small parcels of lands. 

As to the relative use of the two procedures, the 

undefined structure procedure is by far the mot.• 

common practice. Consequently, in a great majority 

of determinations that certain lands are situated 

within the known geologic structure of a producing 

field, the determination is made without the preparation and filing of a plat of the structure. 

The Department has consistently held that 

designation of undefined known geologic structures 

serves to withdraw lapds from noncompetitive leasing. 

Administratively, an undefined structure has the 

same force and effect as the formally defined 

structure approved by the Director. See decisions--

Ernest A. Hanson A-26375 (May 29, 1952); H. E. 

Christensen, A-26221 (August 31, 1951), where applications for noncompetitive leases and preference 

right leases were denied based upon Geological 

Survey reports that the lands were in "undefined 

additions" or "a proposed addition" to the known 

geologic structure of a producing oil pr gas field. 

TERMINATION 

The question is sometimes raised as to the 

significance of the known geologic structure of a 

producing oil and gas field when oil and gas production no longer exists and such field is ostensibly 

abandoned. In unreported decision (A-6287) of 

March 24, 1924, the First Assistant Secretary of the 

Interior stated departmental policy in the matter as 

follows: 

The term "producing oil and gas field" 

as used in section 13 of the leasing act 

must be construed to include areas in which 

there has been production and which are 

capable of producing more oil, otherwise 

cessation of production in a given field 

because of a strike or other external 

matters would render areas which are clearly 

oil bearing, subject to prospecting 

operations * * *· Until further showings 

are made which are persuasive that the area 

does not still contain valuable deposits of 

oil the field will not be redefined. 

For further support of this policy see decision of 

November 10, 1938 (56 I.D. 390). 

When complete exhaustion and abandonment have 

taken place in all productive formations, and the 

capabilities of further production from untested 

sources appear .negligible, the revocation of an 

6 

outstanding definition is deemed unobjectionable. In 

a decision of October 28, 1947 (60 I.D. 62), the 

Assistant Secretary of the Interior stated: 

It is not the policy of the Department 

to redefine a geologic structure until all 

sands or formations therein having prospective value for oil and gas have been 

exhausted or proved barren. 

APPEAL 

Ioasmuch as definitions (defined or undefined) of 

geologic structures are subJect to the unpredictable 

vagaries o:t' nature and to deficiencies in geologic 

information obtainable only after the drilling o:t' 

additional wells, discrepancies are inevitable. Where 

a classification o:t' lands by the Geological Survey is 

disputed by a base applicant, a request for reconsideration or protest may be made to the Director 1 or 

an appeal taken to the Secretary, in the- course ot 

which the person making the request, protest, or 

appeal has the burden ot proving his position by 

competent geologic evidence. 

tlft.DUP .• D.C.M- 358!50