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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).
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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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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
Iys em Series New Albany
Oh io S ha la
Ch at ta no og a S ha le
Shale
In OH..E. KY. In W,VA,.E.TENN,
I n S . IN. .W . K Y,
Roc kfo rd L lmaslone
Lower Jacob~ N
S un bu ry S ha le
Ml$a. Miaa.
Henryvllle Sed
c
Un der wo od Sed
:
Fal ll ng Run B ed
Blg Stone Gap Member :
8 ed lo rd S er ea S eq ue nc e
A
T
u
CleggCreek
T
C le ve la nd S ha le
P
o
Member
:
H
A
P
A
kl
Parllal I
A
Chagrin
o
M id dl e Gr ay
:
D
E
:
Camp Run
N
o
Thr ee Li ck Sed
Shale
Slltatone
Member
v
Equ[-
Member
G
;
0
A
valanl
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HS
s
:
M or ga n T ra il
:
Upper Member
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o
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:
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Shale A
k
Lower Mamber
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k
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Ol en ta ng y S he le
—
Ma rc el lu s S ha le
Mid,
Bloche$”.......
Oev.
Member
Hun ter sv l ll e Cheri l
N ee dm or e S ha le
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 \
>
~ –
IChemunel
Formation
L
B ral l ler F \r ma tl on
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
8/30
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
\
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
8/9/2019 Spe 10791
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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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2800
290
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it9 M
c
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B.F.84 M
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3400
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B.F,OM
A .F. 19 8
6
3600
1
1
.&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 ,, ,
@~ $
fOuU,n*d 2h. laPwdwt im l la791
Y
. ../’” “ “
+)’
. .
E. 0, Ray,1968
I;igut’c 7, ndcx mop:
SII II IC gos fields discussed
8/9/2019 Spe 10791
10/30
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
~
G’
o
0.5
1
,+
*
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
18/30
.
...
->>”
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
19/30
.-
=- “
. <
—--– k----- ----------------------,---
------c- ---—-–
———————-———
—
.
.
.
~-– “ +-=== ‘
.
.*
.
.
.
(
/,4’
“
//
./
0
8/9/2019 Spe 10791
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120
.
*
’20>
.
.—
Jiii52?
20
“
‘-”’-l s“Y\”
L/”-l
, ‘“’ “ “~’
,*,>
-’
..+*’
CONTOUR INTERVAL=10 It
/
.
.
.
.
.
KEvIN LEE,19B0
Figure 18, lsopach map:
Berea-Bedford interval
a
8/9/2019 Spe 10791
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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
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- --
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
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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
Top Related