Note: Descriptions are shown in the official language in which they were submitted.
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ICR-7042
METHOD FOR HYDROCARBON
RESERVOIR IDENTIFICATION
BACKGROUND OF THE INVENTION
5 1. Field of the Invention
The invention relates generally to processing of three-
dimensional seismic data and, more particularly, but not by
way of limitation, it relates to an improved method for
color analysis of 3-D seismic data to identify extent and
location of oil and gas reservoir structure.
2. Description of the Prior Art
The prior art has seen various types of 3-D seismic
surveying schemes with varying forms of data treatment and
it i8 further known to utilize color differentiation to
enhance certdin types of three-dimensional or two-
dimensional seismic data displays. Applicants presently
know of no process for identification of particular reser-
voir seismic attributes which then enable an enlarged reser-
voir display through treatment and color di~play of the
selected seismic attribute data.
SUMMARY OF THE INVENTION
The present invention relates to an improved method for
evaluating seismic data that includes known producing strata
for identification of specific attributes which may then be
used to examine for similar attributes in adjoining three-
dimensional seismic data. Thus, a three-dimensional survey,
i.e. plural, parallel survey lines having known spacing
relationship, and which include within their 3-D section
volume a known producing well and reservoir, is further exa-
mined to derive specific seismic attribute data for use as a
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standard in testing adjacent subterrain data to establish
attribute similarities. The present invention is carried
out utilizing commercially available computer equipment in
conjunction with known forms of video plotter, such equip-
ment being programmed to carry out the method of the presentinvention~
Therefore, it is an object of the present invention to
provide a method for examining three-dimensional seismic
data to establish existence and boundaries of reservoirs
containing the hydrocarbons.
It is also an object of the present invention to pro-
vide a method of producing a color display of a three-
dimensional earth sector with color differentiated
indication of oil and gas reservoir sub-strata.
F~nally, it is an object of the present invention to
provide a digital computer implemented digital process for
examining exi~ting three-dimensional seismic data in rela-
tion to known and established producing hydrocarbon wells
within the sector thereby to identify other reservoir volu-
mes or continuation and extent of reservoir volumes.
Other objecta and advantages of the invention will be
evident from the following detailed description when read in
conjunction with the accompanying drawings which illustrate
the invention~
BRIEF UESCRIPTION OF THE DRAWINGS
FIG. 1 is an idealized view of a sector of earth sur-
face beneath a water covered area having well bores indi-
cated therein;
FIG. 2 is a flow diagram of the program implementation
for carrying out the method of the present invention;
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FIG. 3 is an output display of three-dimensional
seismic data for a selected time window of the earth volume
of FIG. l;
FIG. 4 is an output display of three-dimensional
seismic data for a shallower time window through the earth
volume of FIG. l; and
FIG. 5 is a black and white representation of a multi-
color display, including gradient color bar, as constructed
in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
In general, the present invention provides a data pro-
cessing technique for examining seismic data in the area of
an established well or known hydrocarbon reservoir in order
to establish areal boundaries of such sub-surface reservoir
lS as well as to a~certain spacing and location for additional
wells in the area. After establishment of a first, success-
ful well drilling at a particular area, the present inven-
tion utilizes re-examination of related seismic data,
especially three-dimensional seismic data, thereby to
further enlarge information about the size and shape of the
hydrocarbon reservoir. Information derived is then valuable
in placing offset wells with maximum success a~d reliabi-
lity, proving to be a great aid in the development of oil
and gas fields.
The technique may be divided generally into three
steps. First, previous seismic data, e.g. 3-D data, is exa-
mined to identify seismic attributes from the reservoir
reflection package that can be used thereafter to define a
critical parameter for that reservoir. For example, pre-
vious data may show that any of pay thickness, stratum poro-
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sity, etc. give rise to a critical parameter that is
identifiable to distinguish the oil-bearing stratum or
reservoir sector. In a given case, which is exemplified
throughout this presentation, seismic modeling studies of
data in the area of a newly established well showed that the
amplitude of the trough of data reflected from the top of
the reservoir stratum was related to the amount of pay in
the reservoirs.
In the second ste~ then, the seismic data was examined
to establish a time window or series of time windows across
3-D seismic data in which the critical parameter would be
present relative to the reservoir data. A search of the
seismic data within the defined time windows is then carried
out for the seismic attribute of interest, in the example
here it was examined for critical trough amplitude, and the
trou~h a~plitude values of the seismic attribute are saved
for each trace. Then, the seismic data is searched to pick
hi~hest trough amplitudes within a single defined time win-
dow and this amplitude is saved for each trace o~ the three-
dimensional array.
Finally, step three carries out the display of theseismic attribute values relative to one another on a plan
view display, i.e. generally in a horizontal plan disposi-
tion of X-Y coordinate and the relati~e X, ~ position within
the 3-D survey of each attribute is used to generate such a
plan view display. The relative values of the attributes
are shown by mapping the values to a defined color bar. In
a case to be discussed hereinafter, the trough amplitudes
were displayed in color differentiation, particularly in
scaled Applicon plot6 with color indicating the value of
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each trough amplitude relative to the rest of the trough
amplitudes.
FIG. 1 illustrates a water-covered earth area 10 haviny
sea bottom 12 and subterranean earth structure 14 therebe-
low. For illustration purposes, a particular porous sandstratum 16 having upper interface 18 and lower interface 20
is shown wi~hin earth structure 14.
A wild cat or first well 22 has been drilled as from
sea bottom bore entry 24 to a successful pay zone or reser-
voir area 42 within porous stratum 160 Selection ofdrilling location for weil bore 38 would have been made by
conventlonal practices utilizing prior seismic data
interpretations or the like. In any event, the well 38 has
proven to be a valuable well with probable good reserves of
hydrocarbon. Additional offset dry holes 30 and 32 were
each drilled after successive data evaluations and well site
selectlons at sea bottom locations 36 and 38, respectively.
Utilizing the method of the present invention, a fourth well
22 at sea bottom location 24 was drilled to an up dip for-
matlon of porous stratum 16, as at area 26, and this wellal~o proved to be good pay as previously indicated by color
display of attribute data constructed in accordance with the
present method. Since the first well development, and not
illustrated in FIG. 1, additional successful oil and gas
wells have been drllled in the same field depicted in FIG.
1, and such drill sites have been selected in accordance
with reservoir attribute evaluation in accordance with the
present invention.
In an earth sector of interest, such as earth sector 10
of FIG. 1, 3-D seismic energy data may be available or it
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may be specifically obtained for the purpose of evaluating
the sector. Thus, and referring to sector 10, a plurality
of spatially related seismic sections would be run along a
plurality of parallel survey lines 50, 52, 54 . c . 56 which
extend across the ~urface of earth sector 10 to a selected
termination point or boundary such as line 58. In the case
of earth sector 10, the seismic surveys would be run by
linear marine sounding traverses as a line of successive
source generations and signal receptions along each survey
line is effected. After pre-processing, dynamic correction,
normalization, stacking or whatever the selected procedures,
the seismic data along each survey line would be established
as a seismic section, probably of common depth point aligned
data. Further proces~ing with observance to the spacing
15 between survey lines 50, 52, 54, etc., then enables cross
relationship of the data into a three-dimensional data set.
In performing the present method, the 3-D data set
reuresenting in ~ubstance the matter as shown yenerally in
FIG. 1, would be considered to determine a critical para-
meter exhibiting a hybrid seismic response for that dataaround reservoir area 26, the known hydrocarbon producer and
the original well drilled in the sector 10. There are
various seismic data processing methods and treatments which
may be utillzed by the geophysicist to isolate the desirable
critical parameter and it will probably result that the
operator will actually have a choice of critical parameters
for use, and for proving result with balance of one critical
parameter against the other. In the subject case, as pre-
viously mentioned, a very clear cut critical parameter ~as
indicated by the maximum amplitudes oi the data trough as
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reflected from the top of the reservoir stratum as this was
directly related to the amount of pay in the reservoir
structure.
FIG. 2 illustrates a basic data processing flow diagram
which is readily implemented by the skilled artisan to per-
form the necessary processing and outputing steps to imple-
ment the present invention. Present practice utilizes a
proyrammed digital computer, a Model 760 CYBER Digital
Computer as is commercially available from Control Data
Corporation. And visual output of the display is effected
on such as an Applicon Plotter, available from Applicon,
Incorporated of Burlington, Massachusetts. Other digital
computers and image processing equipment may readily he
programmed and utilized to carry out the invention ~o the
similar result. In particular, the I2S Model 70 Image
Procas~ Computer as produced by International Imaging
Syetems, is particularly effective as it enables a very
large range of color hue, value and chroma assignments.
Referring to FIG. 2, the seismic data is input at stage
70 as pre-processed and assembled three-dimensional seismic
data for the earth volume of interest. The seismic data
input will have been previously examined to select the
desired critical parameter; for example, in the example
ca~e, previous seismic modeling studies reveal that the
amplitude of the trough reflected from the top of the reser-
voir was related to the amount of pay within the reservoir.
A time window is then selected from the known downward tra-
vel ti~es in the seismic data, such window being selected to
envelope the travel time to the top of the reservoir struc-
ture of interest.
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Each individual trace of the input 3-D seismic traces
is then examined through the time window portion to select a
critical parameter value, e.g. the largest, within the win-
dow and the value for each trace is output to stage 76
whereupon the time window trace value is stored at a
selected grid position that i5 related to the X-Y coor-
dinates of the earth sector, e.g. a horizontal slice through
earth sector 10 at approximately the depth of reservoir area
26. Once the grid is filled for the total cros~-section,
the grid of values is scaled in some selected manner, i.e.
the range of values for the critical parameter as assigned
to res~ective ones of a plurality of color quality values,
e.g. inten~ity, hue or the like is carried out in stage 78.
The scaled grid values are then output to display in stage
lS 80 to reveal a plan view indication of the critical para-
meter of interest. the operation on the aeismic data may be
carried out a plurality of times at a plurality of different
selected time windows, each selection of which is intended
to reveal still more information as to the dip and/or con-
volution of the oil bearing earth structure. With each dif-
ferent time window, new and different information relative
to critical parameter of reservoir top structures will be
revealed, and a directionally related pattern soon develops
to reveal the essentlal structure acros3 the cntire earth
sector that i9 being examined.
FIGs. 3, 4 and 5 represent actual output displays for
the earth sector 10 of FIG. 1. In FIGs. 3 and 4, black and
white are reversed for purposes of the depiction. Keep in
mind that the original well 22 gave rise to the subse~went
examinat~on in accordance with the present invention with a
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view towards developing the field and drilling additional
wells. Previous data inspection showed that the amplitude
of the troughs was the critical parameter and 3-D seismic
data for the sector was examined in the manner of the inven-
tion. An examination of peaks of troughs at a time windowextending from 2.175 - 2.260 seconds depth resulted in a
display pattern such as that shown in FIG. 4. It can be
readily noted that the original oil well 22 is exactly on
indication and that the previously selected dry holes 30 and
32 have indeed missed the reservoir sands. In FIG. 3, a
subsequent examination of the 3-D data at a selected time
window of 2.268 - 2.372 seconds depth, i.e. a position
deeper than the previous time cut dictated by reservoir area
26, revealed a down-dip of the reservoir as well as a very
large and consistent reservoir lower indication. A sub-
sequent drilling of well 38 based on the indication of FIG.
4 proved out in that a good producing oil well was obtained.
FIG. 5 provides a black and white illustration of a
multi-color output display of the data ~imilar to that out-
put in black and white in FIGs. 3 and 4. The same 3-D
seismic data is utilized and examined over a number o~
selected time windows bracketing the approximate depth of
the top of the reservoir of interest, interface 18 of FIG.
1, and the detected maximum trouyh values for each tirne win
dow are scaled on the grid. Output of the grid is then
carried out on such as the Applicon Plotter with grid output
values ranging from dark magenta at color bar 82 through the
red, yellow and cyan hues to a bright color bar white 84.
As can be seen from the tonal gradations, there are thirteen
different hue/intensity combinations across the color bar
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and these are effected on the output display in accordance
with the scaled value for each individual picture element or
pixel. The background of FIG. 5 is dark magenta indicative
of low scale values, and the spot indications relating to
reservoir top structures shade through reds and greens to
white at the highest scale indications.
The foregoing discloses a novel seismic data processing
technique wherein three-dimensional data in surround of a
producing well can be further examined to isolate attributes
and outline hydrocarbon reservoir structure. The method has
proven particularly effective in aiding well-site selection
in developing oil fields. Proper picking of attributes and
subsequent time window examinations of 3-D data can vir-
tually eliminate drilling of dry development wells.
Changes may be made in combination and arrangement of
elements as heretofore set forth in the specification and
shown in the drawings; it being understood that changes may
be made in the embodiments disclosed without departing from
the spirit and scope of the invention.
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