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t

,

SPE/DOE

ociety of

U.S. Department

Petroleum Engh’rears

of Energy

SPE/DOE 10791

A Detailed Geologic Study of Three Fractured Devonian Shale Gas

Fields in the Appalachian Basin

by Robert C, Shumaker,

West Virginia University

The paper was presented al the SPE/DOE Unconventional

GasRecoverySymposium

f

theSocietyofpetroleumEngineers

held in Pittsburgh.

PA. May 16-18.1982.

Thematerialissubjecf10Correchony the author.Permission10copyis restricted

to2n abstract of not more than 300

words. Write’ 6200 N. Central Expwy., Dallas, TX 75206.

ABSTRACT

deposit and as discreet fields in western West

Virginia and Ohio (Figure 4). It is only the

Analysis of three shale gas fields illustrates

production of southwestern Nest Virginia and eastern

the importance of basement structure in developing Kentucky that is the subject of this report, The

fracture permeability within the thick Devonian

fields there have produced over one trillion cubic

shales of the Appalachian basin. A porous fracture feet during the last fifty years, but the shale

facies within the organic rich lower Huron shale

has produced shallow gas for local consumption for

member of the Ohio Shale relates to a regional stress

over 100 years in several areas of the eastern

field created by differential shortening of overlying

United States. Expl~~atory gas wells are shallow,

sedimentary section across the lower Huron detachment

being located randomly, either in proximity to

zone during the Alleghanian deformation.

Greater

other producing wells or on the basis of available

permeability (commercial) occurs near the outer

acreage in

or at the margin of the ~roductive area.

margin of tectonic shortening.

Linear trends of

Geologists have generally reasoned that fractures

wells with abnormally high final open flows relate

create the permeability within the shale of the

to linear trends of highly fractured shale. These

study area, and that they are necessary to release

trends were probably caused by unique stress fields

the entrapped gas in commercial quaWities.

created along flexures in the shale above basement

fault zones. The U.S. Department of Energy undertook an

INTRODUCTION

evaluation of the importance of geologic structure

to:

(1) the formation of fractures within the

shale, and (2) the production of gas from the

The Devonian shale is an informal stratigraphic

shale. This paper reports on the results of this

name applied to a body of organic clay-rich sediments

study which is a part of a much broader U.S. DOE

that extend across nearly 25% of the North American

program that undertook a total characterization of

continent. This black and gray shale generally lies

the eastern gas shales.

between Mississippian sands or shales and Middle

Devonian limestones. The shales onlap these car-

DISCUSSION

bonates along an erosional surface of low relief.

Two aspects of our structural study are

The thin shale is usually called the lVoodford particularly interesting in regard to understanding

shale in basins of the western plain states, In the

the relationships between shale gas production and

Illinois basin (Figure 1) the shale is called the

geologic structure. The first result comes from

New Albany shale (3o-1OO meters thick), and in the

the study of fractures Found in oriented cores of

Michigan basin it is called the Antrim shale (25-

the shale by Mark Evansl

40 meters thick). Within the western Appalachian

, and the other comes from

the geologic analysis of three producing shale gas

basin the thick shale sequence (up to 400 meters

fields,

thick) is usually called either the Ohio shale or

the Chattanooga shale (Figure 2). Stratigraphic

The evaluation of fractures found in oriented

problems arise eastward, within the central portion

shale cores, taken from within our study area in

of the Appalachian basin, where the shales change

facies to interbedded sands and silts of the Appa-

the Appalachian basin (Figure 4), has shed light on

the type and distribution of subsurface fractures

lachian Catskill deltaic sequence [Figure 3). in the erogenic foreland, Even though several of

these cores were taken in what initially was

It is only along the western flank of the

Appalachian basin that the Devonian shale produces

considered undeformed foreland sediment, they all

contained vertical natural fractures, joints, to

large quantities of gas. The major areas of produc-

depths of over 6000 feet, and most surprisingly,

tion are in eastern Kentucky in a blanket-like

these cores contained slickensided fractures, small

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,

faults.

In very general terms, the systematic joints

a shear system symmetrically distributed about the

from these cores form three sets: one related to

horizontal stress r irection prevails, but the

present day in-situ stress, which is thought to be fracture trends arc less predictable and trends can

Mesozoic in agcl, and the other two which form an bc more complex.

orthogonal cross and longitudinal joint systcm that

is Alleghanian in age. Generally the orthogonal A reduction in production is found cratonward

joint pattern bccomcs more complex toward the of t}le commercial shale production.

This may relate

southern productive area of eastern Kentucky,

This is

to proximity of the shale outcrop, However, cores

precisely where the highest areal production occurs, taken of the shale in that area show a notable

The strac, slickcnlincs, on the shear fractures arc

decrease in the numbers of slickensided surfaces

subparallel to the cross joint set, which suggests and a decrcasc in frequency of open or mineralized

a common origin for the entire fracture pattern.

joints, The regional joint pattern of this area

However, complexities in the fracture patterns

could be characterized as a simple orthogonal

found in eastern Kentucky imply more than one stress

system which should be less productive.

There

episode.

Shumakcr2 suggested that open and mincral-

appcars to be, then, a distinct lateral change in

ized fractures were most prevalent in the highly

the nature and permeability of the pattern across

organic portions of the shale based on studies of the basin with the complex orthogonal/shear pattern

the first few oriented cores.

Evansl showed that

segment being the most productive.

the open and mineralized joints within the shale

were most numerous in the highly organic portions

A

second aspect of our investigation that has

of the section based on 13 cored wells, and he

application to shale gas exploration and exploitation

generally supported the proposal that production

comes from a detailed analyses of production and

comes from partially mineralized vertical fractures

structure of three gas field areas (Figure 7). Two

of a porous fracture facies within t ~e highly organic

of these areas are distinct fields at the northern

shales in the lower portion of the Devonian shale.

margin of the main productive area, whereas, the

“Ile more intensely fractured shale section in the third is within the main producing area of the

commercially productive area is interpreted to

Big Sandy field in eastern Kentucky.

contain a decollcmcnt surface, or perhaps more

aptly, a zone of differential shortening across the Detailed investigations of the Nidway-Extra

organic shales.

TI~c differential shortening field of Putnam County, Nest Virginia, by William

creating the fractures is found in the distal portion h’, Sc}~aefer4 established a direct relationship

of a more extensive area of transport and shortening

between production from the organic portion of the

above decollcment surfaces that extends deeper into Devonian shale (the lower Huron shale) and the

the section in the more deformed eastern Appalachian structural trend (Figure 8) of the field.

Schaefer

basin (Figure S).

?Iis detachment extends into the was able to confirm that initial and final open flows,

core area of the Appalachian orogcnic belt, as would flows after explosive frac (Figure 9), from wells

be expected, if the fractures relate to the cul- at Nidway-Extra arc greatest along the northwestern

minating orogcnic event, the Alleghanian orogeny.

limb of the very low relief Nidway anticline. The

An important limiting factor to the commercial

production is greatest near the flex line of the

adjacent syncline, off-structure.

}{e also found a

production from the organic shale is the vertical lesser increase in production along the southeastern

extent of the fracture facies in the organic shale

1imb,

The striking similarities of high flow rates

zones. The enclosing shales form part of the source,

with structural position along the fold is forcibly

and they also form a scul to the organic shale rescr-

brought out by comparing Figures taken directly from

voir.

It is important to generally maintain the

Schaeferls text4.

Furthermore, he showed that the

seal integrity during well completion treatment

thickening of the lower Huron shale (Figure 10),

and stimulation in order that water from porous

the primary reservoir, into the adjacent syncline

adjacent formations does not enter the chemically

suggests growth of the structure during sedimentation,

sensitive shale reservoir (Figure 6),

tle interpreted this to mean that basement deformation

was an important factor in the formation of the

In plotting the areal distribution of fracture

Nidway anticline, From these data (Figures 8, 9 and

patterns, it was found t}lat most of t}lc present day

10) at the Nidway-llxtra field, one cannot be abso-

commcrcial production falls within an area of lutcly certain if it is the thicker lower Huron

limited tectonic transport, This area is character-

organic shale or if it is fracturing associated with

izcd by the prcscncc of a complex orthogonal frac-

thc folcling which contributes most to the noticeable

turc system that includes inclined slickcnsidcd

incrcasc of off-structure flow rate,

One might

fractures, Only limited production is found in

argue that even if fractures are present, they are

the zone of more extensive tectonic transport to

not necessarily structural in origin.

Such fractures

the cast within the highly deformed portion of the

could be caused either by Iithologic factors, such

orogcnic forcland,

Production from this area is

as composition, or as the result of differential

characterized by hi.ghcr than

normal

pressure from

fracture zones of little sustained production. In

compaction of thin shale on, and thick shale off

structure. Regardless of the cause, an empirical

shales of that area horizontal slickcnsi~ics predom-

exploration rationale was proposed based on Schaeferts

inatc in the transport zone, but inclined slickcnsidcs

stucly,4 Direct cvidcncc for the exact and underlying

arc also very

common. The

fracture pattern js cause for this increased production of off-structure

strongly oriented, more intense, penetrative, and

WC1lS was elusive even though Schaefer had suggested

poles to slickcnsidcd surfaces plot in a girdled

the fractures were structural in origin, and he made

distribution with maxima related to normill faults

a major guiding breakthrough for an empirical explor-

and to the primary tind Rciclcl shcur directions,

ation rationale.

In the more productive urea of minimal transport

.+,l

(u

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*

If one combines the knowledge gained at the

Using re-interpreted Cottageville as background,

Midway-Extra field with what is known of the one can now go back to Midway-Extra and suggest

Cottageville Fields,

then additional insight is

that the northwestern flank of that structure is

obtained into the specific cause of commercial

faulted at the basement level.

The justification

shale gas production for that portion of I est for this interpretation is the growth aspect of

Virginia (Figure 7). /\t first glance, the structural

the structure and location of the high productivity

similarity between Cottagcvillc and the Nidway-llxtra

wells.

At Cottageville such WC1lS are located along

field is not striking.

Structurally, the Cottagc-

and above a proven basement fault. If one concludes

vine field appears to lic along a very low rcli’:f

that the Midway-Extra field is faulted on both

monoclinal flcxure on a southeast dipping regional

flanks then the marked asymmetry of production is

slope (Figure 11),

Nartin and Nuckols6 suggested

puzzling. This asymmetry may relate to Alleghanian

that the cause for the flexurc was a basement fault.

stress being concentrated on the western flank of

Detailed interpretation of seismic data collcctcd

that structure to create anomalously fractured shale

by Geophysical Services Incorporated by Glenn

in the detached reservoir horizon along that trend.

Sundhcimcr7 (Figure 12) confirmed the presence of

However, it may relate to intersecting structural

a flexure in the sediments and a basement fault

trends on that flank which create a more complex

directly under the trend of the most productive fracture pattern and more permeability there.

WC1lS along the southeastern flank of the Cottage-

Clearly, Nidway-Extra and Cottageville document

vine field (compare Figures 12 and 13). Note the

the importance of geologic structure and specifically,

southeast regional dip and the subdued flexure

basement faulting, to increased fracture pcrmea-

including a synclinc just updip, northwest from

bility and high production trends from the shale.

the fault (Figure 12).

These structures are similar,

The productive asymmetry suggests an interplay with

although not identical, to ones mapped by Kutner8 detached Alleghanian deformation along the margin

from detailed subsurface geologic data. Nuck~ls9

of the pre-existing basement derived faults or

has found that sedimentary patterns of the organic intersecting fracture trends. It further suggests

shales are complex around this structure,

His

that the permeability in the detachment horizon,

maps also show that the best production does not

the porous fracture facies, is not a uniform blanket

uniquely follow the thickest lower Huron organic permeability for this part of Nest Virginia. If

shale section. The best production is westward, it were, then production would be found on the

up dip, along the fault as mapped by Sundheimer7

crest of the structure.

(Figure 12).

If onc eliminates the regional dip

from Sundheimer’s isotimc structure map, then the The compilation of detailed geologic structure

Cottageville field becomes a low fold with flanking maps for Martin County provides sufficient data to

synclincs.

It is only then that the Cottageville

test the applicability of interpretations made at

field appears similar to the Midway-Extra field, but

Cottageville and Midway-Extra to a third study area

Cottageville has lCSS relief, Keeping the relation-

which lays at the northern margin of the Big Sandy

ship at Nidway-Extra in mind, compare the position

gas field (Figure 7).

The data for the analysis of

of the fault, the fold crestal trace, and the trace this area comes from subsurface fracture data of

of the flanking northern syncline with the production Evansl; the surface structure map and raw data

trends at Cottageville as mapped by de h’ys and compiled by Leell;

the surface structure trends of

Shumakers (Figures 13 and 14). There is a marked Long12; the production data compiled by J. Negus-

similarity of final open flow trends at didway-

de lfys13;

the unpublished isopach and structure n,aps

Extra with production as mapped at Cottageville.

of Lannan and Okoye; and the senior authorts efforts

This similarity is accentuated by lower productivity at re-interpreting certain of these maps.

along the crest of both structures, At Cottagcville

there is a near coincidence of productive trends The subsurface structure of the area, as mapped

shown on the summary trend map (Figure 15) above by Lecll, shows the west trending broad Warfield

and parallel to the basement fault, The trends are

anticline and fault entering the county on its

not nearly as numerous for the northern synclinc

eastern margin (Figure 16). The fold plunges

(Figl’re 15) which, incidentally, maybe the southwest westward and a parallel trending surface fault

terminus of another buried fault.

In the case of

terminates near a north-south trending low which

Cottagevillc, the identity bctwccn structure and

LCC1l interprets as a strike-slip basement fault. A

production seems far more conclusive than that at continuation of the Narficld anticline rises westward

;didway-Extra simply

bccausc of

the greater quality

from the structural low. This anticline is often

and quantity of data. At Cottagcvillc it is clear

conncctcd to the Irvine-Paint Creek anticlinal trend

that better WC1lS, by all production statistics,

(Figure 7), The surface h’arfield fault, which

occur off-structure and that the best wells generally

Lecll interpreted to be a detached thrust fault,

occur directly above the basement fault.

Dc h’ys and

seemingly terminates near the same north-south

ShumakcrS contoured the production data at Cottagc-

trending structural low, However, the steep southern

villc with a mechanical style in that preliminary

flank of the Itarfield, which is an cast-west trending

investigation attempting to avoid bias in their

monoclinal flcxure, nrobably reflects a basement

contouring, Had they contoured the production

fault that continues westward across the intersecting

data as Schacfcr did with final open flows at

10W. That these are major basement structures is

Miclway-Extra, and if they had both Schaefer’s results

suggested by their influence on sedimentation

and Glenn Sundhcimcr’s ma}~when contouring the (Shumakcr14), the paralleling magnetic intensity

Cottagcvillc data in 1977, thc n they would }]avc

trends (ShutnakcrlO), and the adjacent east-west

contoured the Cottagcvillc data to a more linear

trending basement faults which arc part of the

trend, and the identity of structure and production

eastern Kentucky fault systcm (Pigurc 7). If the

trends would hc more striking.

interrelationship bctwccn basement structure and

production found at the previous two fields holds

ii

,

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here, then increased production should bc found along

growt.n faulting .nhances local fracture density

the synclinal structure and at the base of the creating areas and trends of greater production.

monocline at their flex lines.

Areas and trends of

Don Nea115 expanded the impact of our work by

high production (Figure 17)do correspond very closely

noting the coincidence of higher initial open flows

to the north-south trending structural low (Figure from shale gas wells located on the flanks of

16) .

As noted there is a correspondence between

other geological structures elsewhere in southern

structure and sedimentation so that the production

West Virginia.

Our study also suggests that inter-

also parallels certain stratigraphic trends (compare

sccting structural trends may be favorable areas

Figures 16, 17 and 18).

There is a suggestion that for exploration.

the areas of highest gas flow occur at the inter-

sections of east-west trending lows with the north- It is not suggested that exploration rationales,

south trending saddle.

The relationship of final

developed through this analysis of the Appalachian

open flows with structure is similar to that found

basin, present unique solutions for the location

at Cotcageville and Midway-Extra, but in this

of fracture porosity in organic shales. However,

case one cannot rule out the possibility that part,

our models do form a basis of exploration for

or even all of the increased production relates

fractured reservoirs in erogenic forelands, and

to sedimentary loading and distortion by the Berea they should at least be considered viable exploration

sand channel that follows the structural low. If

rationales for these areas.

production comes from the shale directly beneath

th,e Berea, rather than the deeper Lo~ier Huron, then

The application of the rationales developed

one would consider the loading phenomena to be

within the Appalachian foreland trough to the

important. Detailed production data are not

interior basins of the continental United States,

available to the author which would be necessary

which probably lacks detached horizontal transport,

to determine the stratigra hic position of the

is open to question. Based on the results of this

production, Negus-de Wys1? showed a high calcium-

study, it would appear that a highly permeable

magnesium geochemical anomaly from the shale within

regional fracture porosity is less likely there, but

this area. This suggests that secondary mineral

that the flanks of flexures over normal faults,

propping may be important to gas production just particularly at intersecting basement fault trends,

as it is at Cottageville and Midway-Extra. The should be prospective, If a portion of the shale

east-west trending monocline’ which forms the acts as a seal for a lithologically controlled

southern flank of the anticline and which probably

porous fracture facies, then it also seems reasonable

is a basement fault, also affects shale gas produc-

to presume that faults of small throw and/or mono-

tion, but there is not a perfect correlation between

clinal flexures would be the most prospective

the trends. Not all wells are large producers,

structural features. If such flanks of geological

This is not unprecedented as not all basement faults

structures do hold hydrocarbons, then it is essen-

are reflected by high production from the shale.

tial that well completion treatmeni.s of limited

On trend, in the adjacent county to the west,

size be designed to preserve that adjacent seal in

production visibly increases along an extension of order to limit entry of chemically incompatible

this flexure. These observations suggest that the formation water into the fractured reservoir.

relationships between production and structure

established to the north at Cottageville and Midway- ACKNOWLEDGMENTS

Extra apply equally well in the eastern Kentucky

area. However, further analysis is required within The author wishes to acknowledge the U.S.

the heart of the Big Sandy field to determine if

Department of Energy for their financial support

they hold there.

of this research, and in particular, he wishes t~

thank technical progress officers Charles Komar,

CONCLUSIONS

William Overbey, Arlen Hunt, and Claude De?.n of the

Morgantown Energy Technology Center for all of

The results of DOE sponsored research show that

their assistance over the past five years. The

a sufficient thickness of organic shale and a proper basis for this report is rooted in the research

thermal maturation of the shale are prerequisites and efforts of fellow faculty, staff, and graduate

for potential commercial production, but that within

students who worked on the

DOE

grant at West Virginia

the study area, it is the presence of open natural University. Many scientists assisted our progress

fractures which determines the quantity of gas

during the life of the project, but of special

produced.

Based on analysis of shale cores we

significance to the results reported in this paper

suggest that it is the organic portions of the

were the efforts of: Russell Wheeler, Mark Evans,

Devonian shale, primarily the lower Huron shale,

David Kutner, Kevin Lee, Brian Long, Jane Negus-

which contains a porous fracture facies that forms

de Wys, William Schaefer, and Tom Wilson.

the primary reservoir for regional shale gas

production in West Virginia and eastern Kentucky.

REFERENCES

Commercail production, by 1979 standards, in the

study area of the Appalachian basin coincides with

1.

Evans, Mark A.:

  Fractures in oriented

Devonian

a zone of limited tectonic transport near the ter- shale cores from the Appalachian basin”, West

minus of more extensive detached transport of

Virginia University Department of Geology and

sediments found to the east, in the Appalachian Geography Nasters Thesis, Norgantown, 277 p,

foreland. This commercial zone is characterized

(1980) ,

by inclined slickensided fractures and conjugate

systems of mineral-propped vertical joints, Our

analyses of three producing shale gas fields in the

Appalachian basin further indicates that basement

40

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2. Shumaker, Robert C.:

“Porous fracture facies

12. Long, B. R.:

“Regional survey of surface joints

in the Devonian shales of eastern Kentucky and

in eastern Kentucky”, DOE/METC/UGRFile No. 195,

West Virginia”: The Caledonides in the U.S.A.,

West Virginia University Department of

proceeding volume I.G.C.P, project meeting

Geology and Geography Nasters Thesis, Morgantown,

at Virginia Polytechnic Institute and State

66 p. (1979).

University Geological Sciences 4emoir No. 2,

p. 18 (1979).

13.

Negus-de Wys, Jane:

t The eastern Kentucky gas

field--a geological study of the relationships

3.

Larese, Richard E., and Heald, Nilton T.:

of Ohio shale gas occurrences to structure,

 petrography of selected Devonian shale core

stratigraphy, lithology, and inorganic

samples from CGTC 20403 and CGSC 11940 wells,

Lincoln and Jackson Counties, West Virginia”,

geochemical parameters”, Morgantown Energy

Technology Center’s UGR File No. 262, West

United States Technical Information Center,

Virginia University Department of Geology and

U.S. Department of Energy Research and

Geography Ph.D. Dissertation, Morgantown,

Development Administration, NERC/CR-77/6, 27 p.

199 p. (1980).

(1977] .

14.

Shumaker, Robert C.:

 l~e effect of basement

4. Schaefer, William W.: “G:ology and producing structure on sedimentation and detached

characteristics of certain Devonian brown shales structural trend within the Appalachian basin”,

in the hiidway-Extra field, Putnam County, West

Geological Society of America, abstract for

Virginia”, West Virginia University Department

combined northeastern and southeastern section

of Geology and Geography Masters Thesis, meeting (1982).

Morgantown, 67 p. (1979).

15,

Neal, Donald W,:

“Subsurface stratigraphy of

5. Negus-de Wys, J., and Shumaker, Robert C.: the middle and upper Devonian classic sequence

t pilot study of gas production analYsis methods

in southern West Virginia and its relation to

applied to Cottageville field”, United States gas production”, West Virginia University

Department of Energy, Morgantown Energy

Department of Geology and Geography Ph.D.

Technology Center, MERc/CR-78/6, 45 p. (1978).

Dissertation, Norgantown, 144 p. (1979).

6. Martin, P., and Nuckols, E. B., 111: “Geology

and oil and gas occurrence in the Devonian

shales, northern West Virginia”:

Devonian

shale production and potential, U.S. DOl?/MERC

Special Report, MERC/SP-76/2, p. 20-40 (1976),

7. Sundheimer, Glenn R.: “Seismic analysis of

the Cottageville field”: Second Eastern Gas

Shales Symposium, METC/SP-78/6, v. II, p. 111-

120 (1978),

8. Kutner, David P.: “Evaluation of shallow

structural features ?s they relate to basement

faulting”, West Virginia University Department

of Geology and Geography N,S. Option 11, final

report, Morgantown, problem under .shumaker,

10 p, (1979).

90 Nuckols, E. B., 111:

~~TheCottageville (\ OUIIt

Alto) gas field, Jackson County, West Virginia:

a case study of Devonian shale gas production”,

West Virginia University Department of Geology

and Geography Masters Thesis, Norgantown,

132 p. (1979),

1 Shumaker, Robert. C.:

llForm-line structure and

basement structure maps of the Appalachian

basin--a comparison”: The Caledonides in the

U.S.A.,

proceeding volume I,G,C.P. project

meeting at Virginia Polytechnic Institute and

State University Geological Sciences Memoir

No. 2, p. 18 (1979).

11,

Lee, K. D.:

“Subsurface structure of the eastern

Kentucky gas field”, West Virginia University

Department of Geology and Geography Masters

Thesis, Norgantown, 53 p. (1980),

1 ?

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n

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STRATIGRAPHICUNITS 4SWDV ANDRELATIONSHIPS

TO NEWALBANVSHALEANOCHATTANOOGASHALE

(B fl er Sw ag er , 1978, Pr ovo , 19 77, L ln eb ac k, 1968 , Mi ll er , 19S5, Mc Far lan , 1943 )

Un its of

Un it s 01

Unl ls 01

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Shale

In OH..E. KY. In W,VA,.E.TENN,

I n S . IN. .W . K Y,

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Lower Jacob~ N

S un bu ry S ha le

Ml$a. Miaa.

Henryvllle Sed

c

Un der wo od Sed

:

Fal ll ng Run B ed

Blg Stone Gap Member :

8 ed lo rd S er ea S eq ue nc e

A

T

u

CleggCreek

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C le ve la nd S ha le

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:

H

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P

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kl

Parllal I

A

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:

D

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Camp Run

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Shale

Slltatone

Member

v

Equ[-

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M or ga n T ra il

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Upper Member

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Ol en ta ng y S he le

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Mid,

Bloche$”.......

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Absent

d e WY% 197

Figure 2.

Devonian shale nomenclature: Appalacl]i a“ basin

so:;~asl

W .r thwn Panmnd le

W es t V i fg lnla

I

I

Northeast

Wosl

Virglnla

Schwlo lo rmc, 1977

W*SI

Greenland GaFJ

hl \

>

~ –

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L

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4

arrell

Shale

D,,,,

‘ha,.

m black shit.

~ Nil%’’’” n’on’

m rodbads

~ Iknestmic

and

1’ieww

3. Facies relationships: IIcvonian ehalc

8/9/2019 Spe 10791

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LEGEND

~ Outcrop area of Devonian rocks

~ Devonian Black Shale gas production

m

Contract area

- .,

\

1’

\

\

}

1 Petersburg ~SD ‘

\\

\

{

2 Parsons

\

‘\\

~:’i

rld~

~

/

o

Cored Wells [Evans, 19791

\(

1’”/6 .,

I

———’

I

MARYLAND

NTAIN SYNCLINE

1A

Figure 4. Study area

APPALACHIANBASIN

APPALACHIANFOLD-THRUSTBELT

+3rnlla*Nw

SE+3

+-BIG SANDY SHALE (3AS FIELD~

PINE MUNTAIN THRUST ,Otac

o

I

I

i

.+ ----- ---

\

I

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I

---------

I l_~/ \/-\*, r\-, ~e-i=r,- ______ --

A

--------

7---- 7---

\~/ /\-/~ 1~/\’\/ \ /\w, pRE.CAmBRIAN ,Nl,\/,\ -,s /,\l~I@\ ~1~ 1, , /_\, \ \-, yT

.-. _

“3

StfUMAKER lS7B

Fi.gtlre 5.

:;tructural cross section:

——-

castorn ,: wtuc ;y

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No.12s6

Ail..P9rf..133 M

x

,..

Cai.alm

Den.

[

cl

No.1283

\ ${

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.

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.&m.

oil

Fractured Devoni an Shale wel13, Perry County, Kentucky

FIELD STUDY AREA

y: ‘“-

1. CoUaswilleFteld Mea

2 Mi dw ay Ea l a F ie ld A re a

,,%/

,& +,’

A M al tl n C ou nt y F, .l d A ,, ,

@~ $

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Y

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I;igut’c 7, ndcx mop:

SII II IC gos fields discussed

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o

0

~ ,ntlcllnal fold crest

~

c,1,I 20’

Structural contours on baso

W, Sohstfw, 1079

~ O, I.oww Huron

Figure 8, Subsut’face structure:

Midway-Extra field, W, Vat

8/9/2019 Spe 10791

11/30

I

8

‘T’ ‘

o

-+4

~,1,

s

100 McF/o

W, Sohaofw,1079

~u’x?

9,

Isopotcmtiul map:

final open flow from Dcvoniun SIUIIC

. ——

8/9/2019 Spe 10791

12/30

?

1 a

Antlallnal fold orest

Mllas

w, aohmrq 10?9

8/9/2019 Spe 10791

13/30

Fimre H Subsurface structure:

SURFACE AND SUBSURFACE FRACTURES

COTTAGEVILLE AREA, WV

R C.

S HUM AKE R 1 9S 1

\

K

Surface Fracture Tren& Werner.

197T

\

A

Regional Coal Face Cteat Trerr Interpreted

try Strurnakerfrom W. k Geof@cal Survey

Nap W-11. real.

H

Subsurface Devonian Shale fractures from

0 rk3’ IWLf core

Sotii wfrere taken from

producing horizon onfy. Larese and

Heafd.

1977;

Evans,1980-

. =” - -

Structure on TOIIof Berea SandHone.

Kutner. 197S

--- -- f3asernentFauft Trend

--r-

-.-”

-— - Mapped by Sondheii. 1979

---–- Inferred

  4/—.

.’ ,.J

Outline of CottageuitfeGaa Fietd

: .8

---

CottagevilIe field W Va

8/9/2019 Spe 10791

14/30

,34 COTTAGEVILLE

/

  /

.—

  ’ 295 +-+-::flflyi=y

/’ /“-’”’Os (9,2’

1000 3000 5000

i Sundheimer. 1979

Figure 12.

lsot ime map:

structure on top of basement

8/9/2019 Spe 10791

15/30

M.sson\Jackson

County i County

J

\

i,

\,

/’0

,,0

\

~o

\

7//

“ .

/~ \

MILES

1

\

I

I

.

d

o.

f

o 0.5

~a

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0.5

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,+

*

KILOMETERS

,

f

. . . ----

dc Wys

md

s nummml lwfu

Cl. :20

MMCF

Figure 13.

IsoflOW map:

highest annual production (1st or 2nd year production)

8/9/2019 Spe 10791

16/30

I

Mason \Jackson

County tCounty

\,

/

J

MILES

o 0.5

.<

-

\

$.

u

1

0

0.5

1

‘$

KILOMETERS

 

d e Wys an d Sh um sker ,197S

Cl. :5 MMCF

Figure 14, Isoflow map:

mean annual production

8/9/2019 Spe 10791

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i

KEY

Mason \Jackson

1

Drilling Completion Date

,%

Count ylCounty

2

Highest Annua l P roducti on

3 First Fivo Years Cummclative Production

\

4 Total Cumulative Production

/

5 Mean Annual Production

6 Loss Rotiolst Year

i

7 Loss Ratio 2nd Year

8 Loss Ratio 3rd Year / ) ..2 1:

4

MILES

.

2>0

\

I

i-

-./

}--n

0

0.5

1

\

s

KILOMETERS

1

Modif ied f rom de Wysand Shumaker ,1978

Figure 15.

Production trends: Cottageville, W. Va.

8/9/2019 Spe 10791

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.

...

->>”

WA 4FIELD

-550

.

/

.

,qOQ

/

,,$J

.. . / .nO

““”” ~

.

.

-650

.

.“

0“” “

,,OQ

.

---

-- Trace of Surface Thrust ?

Figure 16,

Subsurface structure:

Martin County, Ky,

,..

8/9/2019 Spe 10791

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.-

=- “

  . <

—--– k----- ----------------------,---

------c- ---—-–

———————-———

—

.

.

.

~-– “ +-=== ‘

.

.*

.

.

.

(

/,4’

“

//

./

0

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120

.

*

’20>

.

.—

Jiii52?

20

“

‘-”’-l s“Y\”

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, ‘“’ “ “~’

,*,>

-’

..+*’

CONTOUR INTERVAL=10 It

/

.

.

.

.

.

KEvIN LEE,19B0

Figure 18, lsopach map:

Berea-Bedford interval

a

8/9/2019 Spe 10791

21/30

SPEIDOE

ociety of

U.S.

Department

Pet ro leu m En gh raer e

o f E ne rg y

SPE/DOE 10792

Reflection Seismology as an Exploration Tool for Fractured Zones

in Gas-Bearing Shale —

Cottageville, West Virginia: A Case Study

by James E. Ruotsala and Richard

T.

Williams, West Virginia University

The paper was presented at the SPE/DOE Unconvenllonal Gas Recovery Symposium of the Society of Petroleum Engineers held m Pittsburgh,

PA, May 16-18.1982. The material ISsubject to correction by the author. Permission 10copy ISrestricted to an abstract of not more than 300

words. Write: 6200 N. Central Expwy., Dallas, TX 75206.

ABSTRACT

study because there is a considerable amount of

data available, including reflection seismic

The Cottageville, Kest Virginia, gas field

data, gas production data and subsurface geologic

produces from the Lo~ier Huron Member of the Ohio

data including two cores. The specific questions

Shale formation of the Upper Devonian. The produc-

answered by this study are: what is the seismic

tion results from increased permeability caused by expression of the gas filled fracture zone at

anomalous fracturing of the shale.

A normal base-

Cottageville;

and what role can reflection seis-

ment fault, which lies below the fracture zone, may

mology most effectively play in exploration and

control fracturing in the shales.

development of field:: similar to Cottageville.

Seismic reflection data obtained in the urea in

The reflection seismic method is the recording

1977 show the fault extending up into the Ordovician.

of acoustic energy that is generated at the surface

These data are also analyzed fo-: seismic velocity

of the earth, portions o.? which return to the

and attenuation anomalies associated with the gas-

surface by reflection an,~ refraction. The packets

producing fracture zone, Gas production occurs in

of reflected energy, called reflection events,

an area several miles long but only about one mile

are of primary intere?c.

The useful measurements

wide,

Increased fracture intensity and presence of

of a reflection event are its travel time from

gas in the shale within this limited area serve to source to receiver, its a~.plitude and polarity,

decrease the shear strength of the rock, decreasing

and its spcctrzl content, These measured quantities

the seismic velocity. Similarly, greater attenuation

depend on the geometry and physical properties of

of the high-frequency components of the seismic

the subsurface,

wave can be expected. Examples from the Cottageville

data showing basement structure and seismic ‘Jelocity

The seismic expression of the fracture zone

and attenuation anomalies associated with gas produc-

at Cottageville is determined by comparison of

tion are presented,

seismic data recorded across the producing zone

with data recorded nearby across a non-productive

An exploration rationale for prospecting for

area and with synthetic seismic data from a model

easterrl shale gas is developed.

Although the total

based on atailable geologic data.

area covered by gas-bearing shales i.n the eastern

United States is large, individual gas fields within COTTAGEVILLEGAS FIELD

this area are relatively small, Reflection seis-

mology is used to target specific exploration wells

The Cottagcville gas field is located in

after reconnaissance by other methods has been done,

Jackson County, Nest Virginia (Figure 1), The

INTRODUCTION

wells produce Devonian shale gas from the Lower

llur6n Member of the Ohio Shale Formation, 3700 feet

below the surface.

The field is an elongate area,

Gas production from the organic rich brown

approximately I z miles wide and 6 miles long that

Devonian shales in the Appalachian Basin has long

trends northeast, as shown on Nuckolsr (1979)

been thought to be controlled by anomalous fracture

initial open gas flow map (Figure 2), The most

porosity and permeability. Successful future

development of this rescurce will depend on the

productive wells (more than 100 Ncf/day) lie in

a 2000 foot wide zone.

ability to map these fracture zones in the subsurface,

Fracturing of the producing Lower Huron is

The research rlcscribed in this report has the

documented in two cores, the locations of which

objcctivc of determining how reflection seismology

arc shown on Figure 2. The Jackson 1371 produced

can be used in prospecting for zones of fracturing.

180 Ncf/day after stimulation (Evans, 1979). Evans

The Cottagcvillc gas field was chosen for a case

loggccl the fractures in this core, distinguishing

A.

8/9/2019 Spe 10791

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betwccrr natural and coring-inciuccd fractures.

the center from both sides of this anomalous zone.

M its minimum,

the velocity is 1S percent less than

The Jackson 1369 initially produced 4,000

that of the interval outside the low velocity zone.

\lcf/daY, interrupting coring, and stabilized at

This velocity reduction is based ton an increase

1,007 Ncf/day (Nuckols, 1979).

Larcse and l{cald

of porosity associated with the presence of gas-

(1977), in a petrographic study of this core, filled fractures.

reported the occurrence of mineralized fractures.

ihe fractures were found to hc partially filled

Synthetic seismograms were constructed by

~tith dolomite, leaving vuggy openings which arc computing raypaths through the model section.

The

generally connected to effect good permeability.

trajectory of a ray, for a given emcrgencc angle

Zrom the source, is governed by Snell’s law and

The seismic data available for this study were

depends on the changes in acoustic velocity

recorded in 1977 by Geophysical Scrviccs, Inc. (GSI), encountered along its path. Travel times of

under contract to the Department of Energy.

The

reflection events were computed by integrating the

field procedure

was

GSI’S SIISLOOP1 method, a length riividcd by velocity along the raypath. Am-

configuration designed to provide areal covcragc

plitude and polarity of the reflection events were

of the subsurface.

Reflection points (stack bins)

computed from the velocity contrast acrosz the

arc distr butcd over an area of 12 square miles. A reflecting interface. The resulting reflectivity

L’IRI{OS[;IS- source was utilized, with three vibrators

function was convolved with a wavclet to produce

in-line, sweeping 60 to 20 Ilz.

There were 48 gec-

a synthetic seiscic trace.

Synthetic traces from

phone groups in the rccciving array set out on roads

a number of ray paths reflcctcd by the lower four

and trails, forming a loop. The spacing bctwccn interfaces were combined to produce a synthetic

gcophone groups was 400 feet and the spacing

seismogram.

bctmcn successive source locations was 220 feet,

each

having 10 to 1S sweeps.

The data from the

A few of the ray paths and the synthetic

sKccps at each source location were summed and

seismogram for the model of Figure 4 are silown in

correlated with tbc 60 - 20 Ilz source sKccp signal.

Figure 5. Each trace is plotted midway between

its source and receiver locations.

The reflection

The processing clone by GSI included 3-d mi~ra-

cvcnts for those ray paths that pass through the

tion, co:~mon depth point stack and time-varying low velocity zone are delayed, This results in

d:convol~tion, This interpretation includc[i con-

kinking of tile two lower reflectors on the seis-

struction of isotimc maps of eight reflection events

mogranr (Figure 6) computed for a Iatcrally homo-

and computation of average and interval Vclocitics.

gcneous cross section.

ikom these,

various maps were produced, including

depth to each of the reflectors, isopach maps of

In addition to being delayed, tile ray paths

thickness between pairs of reflectors and average which pass through the

l o

velocity zone are

and interval velocity maps.

Sck cral faults in

refracted by it. The low velocity zone acts as

the Prcc~mbrian were intcrprctcd.

a lens, focusing some of the returning rays and

dispersing others.

Tile resulting lateral variation

Sundi]cimcr (1979),

intcrprctcd a normal fault

from the GSI seismic ~iata.

of ray intensity at the surface is manifested as

The seismic expression

anomalous reflection amplitude.

(Figure 3) of the fault extends upifard into the

Ordovician, about 6,000 feet below the producing

i{ccordcd seismic d:t~. wre compared to the

zone in the Devonian. ,\s mappccl by Sundhcimcr, the synthetic scisrnogranrs in an effort to locate the

fault stritics s 55° E and underlies gas production expected anomalies in travel time and ampiitudc.

in the soutilwcst part of the ficl~i.

The southeast

TKO rec~rds illustrating these anomalies are located

block is do~ thrown about 300 feet at its maximum

as sho.un in Figure 2. Record 1 was recorded with

displ:lccmcnt. the scurce at the extreme easterl. end of the profile

with l.he geophonc groups set out to the west

iMY “riMCENODELLISG

CrOSSLIIg the gas-producing Zone.

Record 2 was

rccordcd witil the source at the extreme southern

By pcrfornring ray trace rnodelling, synt}lctic

cnd cf the profile with the gcopilonc groups set out

scisrnic data can bc cornputcd for a gi.~cn geologic

to the northeast.

Record 2 lies outside the gas

nrodcl, The tccbniquc is a rnathcma.tical rcprcscnta-

field.

tion of ti]c propagation of acoustic energy through

the subsurface.

For a nrodcl of spccificd geometry ‘illc scisrnic rccor[is arc shown in Figures 7

and physical prop~rtics :ay paths, travel times,

and 8.

Record 1 is similar to the synthetic scis-

and polarity and amplitude of rcflccti.on events

mogram of Figure 5 in ti~at ti~c reflection from the

arc cornputcd.

Comparison of the resulting syntilctic

lowest intcrfacc ciccrcascs in amplitude going cast

seismogram to rccordcd data is useful in tile intcr-

to west (left to right) and is lost in tile noise

prctation of the rccor(icd data.

Ivcst of trace 14.

Kinking of the event associatcci

with ciclaycd travel time is not c)’idcnt, possibly

,1 mathematical rcprcscntation (i’igurc 4) of

i~ccausc of the poor signal to noise ratio, wilich

a cross-section through the gas field ~~as produ~’e~i is related to the diminished amplitude.

i]y constructing horizontal interfaces rcprcscnti’lg

the upper four reflectors mapped by (XI.

~lcoustic

ilccord ?, which lies outside the ficl[i, is

Velocities

aSSigJ)Cci to the

intervals

i)ctwvcn

similar to tbc synthetic seismogram of’ i:igurc

6, the

reflectors arc laterally ilomogcnco~

8/9/2019 Spe 10791

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ATTENUATIONANDSPECTRALANALYSES

A number of investigators have reported

anomalous attenuation of high frequency acoustic

cr,ergy propagating through rock with gas-filled Pore

spaces. Crowc and Alhilali (1974) discuss models

used to predict attenuation and dispersion of

acoustic energy.

The computed dispersion and

aticnuation for a gas and overlain by a higher

impedance unit.

All three models predicted greater

attenuation for the gas charged sediment than for

the overlying unit.

IIamilton (1972), in a paper

concerning the measurement of comprcssi,mal wave

attenuation in marine sediments, reported that gas

bubbles trapped in pore spaces of sediments have

a marked affect on both velocj.ty and attcntiation.

The affects arc anomalously ~ow velocity and anoma-

lously high attenuation of high frequency energy,

The effects were observed to bc dcpcndcnt on both

the concentraticm aud size of the bubbles.

In an effort to observe the effects of atten-

uation on the Cottagcvillc seismic data, amplitude

spectra in a window across record 1 vere computed.

The windoi,’ was .5 seconds long, with its top in the

producing interval.

The resulting amplitude spectra

are not systematic.

Son.c of the ray paths passing

through the prociucing zone ba)c spectra that arc

:k of Geophysical Services,

Inc.

2Registcred trademark of Continental Oil

Company.

REJTRJNCJLS

1.

-1

. .

3.

4.

.s,

6,

Crowe, C., and K. Alhilali, 1974, Anplitudcs

of seismic events and their dcpendcncc on the

absorption-dispersion pairs of the incdia,

preprint of a paper presented at the 44th

Annual Nceting, Society of Exploration

Geophysicists, Xovembcr 10-14, 1974, Dallas,

Texas.

Evans, Nark A.,

1979, Fractures in oriented

Devonian shale Cores from the j\ppalachian

Basin, MS thesis, JJcpartmcnt of Geology and

Geography, Kest \’irginia IJnivcrsity.

llamilton, E, L., 1972, Comprcssional-wave

attenuation in marine sediments, Geophysics

v, 37,

110.

4, p. 620.

Norgan, ,N. t\. , and G, R. Brrccl, 1980, Three

dimensional scistnic investigation in the

(;ottagcl,illc Field Kcst Virginia fina.. report

for DOE

CO]”itr;lCt,

Sllckols, E. R,, 1979, The Cottagcville olount

Alto) gas field, Jackson County, h’cst Virginia:

A case study of Devonian sbalc gas production,

MS thesis ,Dcpartmcnt of Geology and Gcograpt~y,

Ifcst Virginia ~Oliycrsity,

Sundheimcr, Glenn R,, 1 )79, unpublished

isotimc structural map: top of the basement,

CottagcVillc ficlfl: h’cst Virginia.

31

8/9/2019 Spe 10791

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&

9

arkersburg

WEST VIRGINIA

\

\

‘-

.;-.

I _..-

i

d

—-—-—-- ._

.

~

------- -------

—---- -— -_

I

0“

j

o

0.

 

/“

E

c)

 

--’

Meigs Co.

L

-—

————_

j

[

Ga liaCo.

I

o

*-------

—.%

.

5

0

5

10 15 20

Statute Miles

5

0 5 10 15 20 25 30 ~i,ometer~

—— —

Scale: 1:250,000

Fig. 1—

Location —

Cottageville gas field

8/9/2019 Spe 10791

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.JRCKSON 137 I

I

JFICKSUN 136Y

—

RECORO2

0

2880 mTER.

, s

 

$

1 f lLE

,

,

INITIRL OPEN FLCW

CONTOUR lt4TERVfIL V9R IfW4E 100 - 500 - 1000 MCF/O

NUCKOLS [1279)

Fig. 2 —

Gas production

— Cottageville gas

field

8/9/2019 Spe 10791

26/30

- --

0

.1

.2

.3

.4

.5

).6

w4@J

@O.8

=

1.2

‘1

“1

-1

1

ONER HURON

–— LOWER

ORDOVIC]FIN

Fig, 3-

GSI seismic data crossing production

OF——————

2743 M/SCC

+

U267

M/SEC

4633 3.s0 3

LIY KR

4633 Wxc

HuRON

Fig,

4 —

Model of cross sect[on with low velocity zone

. . .

8/9/2019 Spe 10791

27/30

0

500

[

METERS

0

 

1/ /

////

27W3 M/SEC

n

1{{11

I I / / /

/

CDP (METERS)

500

5580 M/SEC

1OpO

1500

.0

.2

.4

.6

.8

1.0

1,2

Fig.

5 — Synthetic seismogram — model with low velocity zone

.,.

8/9/2019 Spe 10791

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0 1000

lI+H+FEET

o

&i-J$IETERS

0

50@

I

METERS

CDP (METERSI

0

500

1000

1500

1,1

1-

I.’a

1,2

.0

.2

,4

.6

,8

140

1.2

Fig, 6 — Syntheticseismogram — laterally homogeneous model

..*

8/9/2019 Spe 10791

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1,0

.>-

,tl

,

Ll

I11

‘

-

1.2

Fig, 7- Record 1 crosses gas production

8/9/2019 Spe 10791

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,1]

,8

REFLECT

1,

1

1,

-.

—..-

RE ORD OLITSIDE OF FIELD

Fig.

8 — Record 2 outside of the gas field