U.S. patent application number 17/240707 was filed with the patent office on 2021-10-07 for seismic data acquisition using designed non-uniform receiver spacing.
The applicant listed for this patent is ConocoPhillips Company. Invention is credited to Joel D. BREWER, Peter M. EICK.
Application Number | 20210311220 17/240707 |
Document ID | / |
Family ID | 1000005655021 |
Filed Date | 2021-10-07 |
United States Patent
Application |
20210311220 |
Kind Code |
A1 |
EICK; Peter M. ; et
al. |
October 7, 2021 |
SEISMIC DATA ACQUISITION USING DESIGNED NON-UNIFORM RECEIVER
SPACING
Abstract
The presently disclosed technology relates to an arrangement for
seismic acquisition where the spacing between adjacent pairs of
receiver and sources lines is not all the same. Some receiver
and/or source lines and/or receiver and/or source spacings are
larger and some are smaller to provide a higher quality wavefield
reconstruction when covering a larger total area or for a similar
total area of seismic data acquisition, while providing a wavefield
that is optimally sampled by the receivers and sources so that the
wavefield reconstruction is suitable for subsurface imaging
needs.
Inventors: |
EICK; Peter M.; (Houston,
TX) ; BREWER; Joel D.; (Sealy, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ConocoPhillips Company |
Houston |
TX |
US |
|
|
Family ID: |
1000005655021 |
Appl. No.: |
17/240707 |
Filed: |
April 26, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15809838 |
Nov 10, 2017 |
10989826 |
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17240707 |
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|
13156104 |
Jun 8, 2011 |
9846248 |
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15809838 |
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61353089 |
Jun 9, 2010 |
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61353095 |
Jun 9, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01V 1/3826 20130101;
G01V 1/20 20130101 |
International
Class: |
G01V 1/38 20060101
G01V001/38; G01V 1/20 20060101 G01V001/20 |
Claims
1. A method of characterizing a geological subsurface, the method
comprising: obtaining seismic data based on seismic energy detected
by a plurality of seismic receivers in a deliberately non-uniform
arrangement, the seismic energy generated at a plurality of seismic
source points within the survey area, the plurality of seismic
receivers deployed at a plurality of positions within a survey area
according to a seismic survey, the survey area including the
geological subsurface, the plurality of positions of the seismic
survey including a first position for a first seismic receiver, a
second position for a second seismic receiver, and a third position
for a third seismic receiver, the plurality of positions of the
deliberately non-uniform arrangement selected, such that: the first
position for the first seismic receiver is not aligned along a
first direction with the second position for the second seismic
receiver, and the first position for the first seismic receiver is
not aligned along a second direction with the third position for
the third seismic receiver; generating a reconstructed wavefield
representing the geological subsurface, the reconstructed wavefield
generated based on the seismic data, one or more drilling locations
within the survey area being planned based on the reconstructed
wavefield, a natural resource being obtained from the geological
subsurface by drilling at the one or more drilling locations.
2. The method of claim 1, wherein the first seismic receiver and
the second seismic receiver are within a first receiver line.
3. The method of claim 2, wherein the third seismic receiver is
within a second receiver line, the first receiver line being
different from the second receiver line.
4. The method of claim 1, wherein the seismic survey includes a
non-uniform spacing between receiver lines including the plurality
of seismic receivers.
5. The method of claim 1, wherein the second direction is
perpendicular to the first direction.
6. The method of claim 1, wherein the plurality of positions for
the plurality of receivers has a deliberately non-uniform spacing
between pairs of adjacent receivers in at least one of the first
direction or the second direction.
7. The method of claim 6, wherein the deliberately non-uniform
spacing is two-dimensionally non-uniform.
8. The method of claim 1, wherein a smallest spacing distance
between adjacent seismic receivers of the plurality of seismic
receivers is at least five percent less than a largest spacing
distance between the adjacent seismic receivers of the plurality of
seismic receivers, the smallest spacing distance and the largest
spacing distance both measured along one of the first direction or
the second direction.
9. The method of claim 1, wherein each of the plurality of
positions is not randomly selected.
10. The method of claim 1, wherein the reconstructed wavefield is
generated using a statistical linear regression analysis.
11. The method of claim 1, wherein the reconstructed wavefield is
iteratively refined based on measured data from the seismic survey,
the seismic survey being a sparse seismic survey.
12. The method of claim 1, wherein the reconstructed wavefield is
created using a statistical linear regression analysis that
minimizes L0 and L1 norms, such that the reconstructed wavefield
represents an actual wavefield of the geological subsurface.
13. A system for characterizing a geological subsurface, the system
comprising: a plurality of seismic receivers configured to detect
seismic energy within a survey area, the plurality of seismic
receivers deployed at a plurality of positions within the survey
area in a deliberately non-uniform arrangement according to a
seismic survey designed to characterize the geological subsurface;
a first seismic receiver of the plurality of seismic receivers
deployed at a first position of the plurality of positions; a
second seismic receiver of the plurality of seismic receivers
deployed at a second position of the plurality of positions; and a
third seismic receiver of the plurality of seismic receivers
deployed at a third position of the plurality of positions, the
plurality of positions of the deliberately non-uniform arrangement
selected, such that: the first position for the first seismic
receiver is not aligned along a first direction with the second
position for the second seismic receiver, and the first position
for the first seismic receiver is not aligned along a second
direction with the third position for the third seismic
receiver.
14. The system of claim 13, wherein the seismic energy is generated
at one or more seismic source points within the survey area.
15. The system of claim 14, wherein the seismic energy is generated
by one or more vibrator trucks positioned at the one or more
seismic source points.
16. The system of claim 14, wherein the one or more of seismic
source points is uniformly arranged within the survey area.
17. The system of claim 13, wherein each of the plurality of
positions is not randomly selected.
18. The system of claim 13, wherein the plurality of positions are
selected based on one or more synthetic seismic surveys generated
using a computer, each of the one or more synthetic seismic surveys
using a different arrangement of the plurality of seismic
receivers.
19. The system of claim 13, wherein the second direction is
perpendicular to the first direction.
20. The system of claim 13, wherein the plurality of positions for
the plurality of receivers has a deliberately non-uniform spacing
between pairs of adjacent receivers in at least one of the first
direction or the second direction.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/809,838, filed Nov. 10, 2017, which is a
continuation of U.S. patent application Ser. No. 13/156,104, filed
Jun. 8, 2011, now U.S. Pat. No. 9,846,248, which claims priority to
U.S. Provisional Application Nos. 61/353,095 and 61/353,089, both
of which were filed on Jun. 9, 2010. Each of these applications is
incorporated by reference in its entirety herein.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] None.
FIELD
[0003] This invention relates to seismic data acquisition of
geologic structures in the earth and processing the data that is
useful in interpreting the geologic structures.
BACKGROUND
[0004] Seismic data is acquired to investigate and map the
structures and character of geological formations under the earth.
Seismic data is typically gathered by laying out seismic receivers
(e.g., geophones or similar sensors) in a survey area and directing
one or more seismic sources such as vibrator trucks to move from
shot point to shot point and direct seismic energy into the ground.
As the seismic sources direct seismic energy into the earth where
they are reflected and/or refracted by interfaces between
subsurface geological formations the seismic receivers sense the
resulting reflected and/or refracted energy, thereby acquiring
seismic data that provides information about the geological
formations under the ground. Basically a seismic source emits a
wavefield that propagates down through the earth and is reflected
and/or refracted by interfaces between subsurface geological
formations then propagates back to the surface where the receivers
detect and discretely sample the returning, ascending or upcoming
wavefield.
[0005] Typically, thousands of discrete seismic receivers are used
to gather seismic data. The seismic receivers are generally laid
out in lines that are substantially parallel and laterally spaced
at equal distances and uniformly spaced down the line. In this
configuration, uniform coverage of the subsurface is achieved. It
is conventional that receiver spacing along the lines is closer
than the spacing between the lines and that, therefore, the
wavefield detected by the sensors is less well sampled in the
lateral direction (perpendicular to the receiver lines) in most
seismic surveys. The normal ratio of the station spacing to the
line spacing runs between 2 and 30 to 1. This means that the
spacing of the receivers along the line is between half and one
thirtieth the spacing between parallel receiver lines. This is
normally due to the costs and expense of adding additional receiver
lines that can dramatically increase the expense of the survey to
achieve a better sampling of the returning, ascending or upcoming
wavefield.
SUMMARY
[0006] The invention more particularly includes a method of
acquiring seismic data including deploying receivers in a survey
area where each receiver is laterally spaced from one another in
two horizontal directions wherein the lateral spacing in at least
one horizontal direction is deliberately non-uniform and wherein
the spacing between any two seismic receivers in the deliberately
non-uniform direction varies by a distance of at least five percent
between the largest spacing and smallest spacing. The method
further includes directing seismic energy into the ground and
recording reflected and/or refracted seismic data with the deployed
seismic receivers, recovering the measured data from the deployed
seismic receivers, and reconstructing the wavefield from the
recovered data.
[0007] The invention also relates to a method of acquiring seismic
data including deploying receivers in a survey area and identifying
seismic source points within the survey area where each source
point is laterally spaced from one another in two horizontal
directions wherein the lateral spacing in at least one horizontal
direction is deliberately non-uniform and wherein the spacing
between any two seismic source points in the deliberately
non-uniform direction varies by a distance of at least five percent
between the largest spacing and smallest spacing. The method
further includes directing seismic energy into the ground at the
source points and recording reflected and/or refracted seismic data
with the deployed seismic receivers, recovering the measured data
from the deployed seismic receivers, and reconstructing the
wavefield from the recovered data.
[0008] A particular preferred embodiment of the present invention
relates to a method of acquiring seismic data including deploying
receivers in a survey area where each receiver is laterally spaced
from one another in two horizontal directions and identifying
source points wherein each source point is laterally spaced from
one another wherein the lateral spacing for each of the source
points and for each of the receivers is deliberately non-uniform in
at least one horizontal direction and wherein the horizontal
spacing between any two seismic receivers in the deliberately
non-uniform direction varies by a distance of at least five percent
between the largest spacing and smallest spacing and further
wherein the horizontal spacing between any two seismic source
points in the deliberately non-uniform direction varies by a
distance of at least five percent between the largest spacing and
smallest spacing. The method further includes directing seismic
energy into the ground from the source points and recording
reflected and/or refracted seismic data with the deployed seismic
receivers, recovering the measured data from the deployed seismic
receivers, and reconstructing the wavefield from the recovered
data.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The invention, together with further advantages thereof, may
best be understood by reference to the following description taken
in conjunction with the accompanying drawings in which:
[0010] FIG. 1 is schematic top view of a portion of a seismic
survey area showing a conventional arrangement of lines of seismic
receivers with shot points;
[0011] FIG. 2 is schematic top view of a portion of a seismic
survey area showing one inventive arrangement of lines of seismic
receivers with shot points;
[0012] FIG. 3 is schematic top view of a portion of a seismic
survey area showing a second inventive arrangement of lines of
seismic receivers with shot points;
[0013] FIG. 4 is schematic top view of a portion of a seismic
survey area showing a third alternative inventive arrangement of
lines of seismic receivers with shot points;
[0014] FIG. 5 is schematic top view of a portion of a seismic
survey area showing a fourth alternative inventive arrangement of
lines of seismic receivers with shot points;
[0015] FIG. 6 is schematic top view of a portion of a seismic
survey area showing a fifth alternative inventive arrangement of
lines of seismic receivers with variably spaced shotpoints;
[0016] FIG. 7 is a is schematic top view of a portion of a seismic
survey area showing a sixth alternative inventive arrangement of
lines of seismic receivers with shot points;
[0017] FIG. 8 is schematic top view of a portion of a seismic
survey area showing a seventh alternative inventive arrangement of
lines of seismic receivers with shot points;
[0018] FIG. 9 is schematic top view of a portion of a seismic
survey area showing a eighth alternative inventive arrangement of
lines of seismic receivers with shot points;
[0019] FIG. 10 is schematic top view of a portion of a seismic
survey area showing a ninth alternative inventive arrangement of
lines of seismic receivers with shot points; and
[0020] FIG. 11 is schematic top view of a portion of a seismic
survey area showing a tenth alternative inventive arrangement of
lines of seismic receivers with shot points.
DETAILED DESCRIPTION
[0021] Turning now to the preferred arrangement for the present
invention, reference is made to the drawings to enable a more clear
understanding of the invention. However, it is to be understood
that the inventive features and concept may be manifested in other
arrangements and that the scope of the invention is not limited to
the embodiments described or illustrated. The scope of the
invention is intended only to be limited by the scope of the claims
that follow.
[0022] An exemplary conventional seismic data acquisition system is
indicated by the arrow 10 in FIG. 1. The seismic data acquisition
system 10 comprises lines of receivers where eight such lines are
shown and labeled 15A, 15B, 15C, 15D, 15E, 15F, 15G and 15H. The
receiver lines are arranged substantially parallel to one another
and are commonly spaced a common and uniform distance apart. Along
each receiver line are a number of generally evenly spaced
receivers 17, indicated by "x's". Also shown with small circles are
shot points 18 at which the seismic sources would generate and
direct seismic energy into the ground. As arranged, the total
system width of the system 10 is S.sub.1. The width-wise or lateral
receiver line spacing between each adjacent pair of receiver lines
is one seventh of S.sub.1 and indicated as 19.sub.ab, 19.sub.bc,
19.sub.cd, 19.sub.de, 19.sub.ef, 19.sub.fg and 19.sub.gh. In FIG.
1, the receiver line spacing is such that nominally:
19.sub.ab=19.sub.bc=19.sub.cd=19.sub.de=19.sub.ef=19.sub.fg=19.sub.gh.
[0023] In accordance with the present invention, it has been found
that even or equal receiver line spacing may not be most optimal
for acquiring seismic data. Noise in the data set may be most
readily identified by even spacing and therefore fairly easily
filtered or cancelled in post acquisition processing. But highly
non-uniform or irregular spacing may actually provide better
results in general. Additionally it has been found that the
wavefield sensed in the lateral dimension (perpendicular to the
receiver lines) by the receivers can be better and more accurately
reconstructed if the receivers are spaced in a highly non-uniform
or irregular spacing.
[0024] The reason for this is the method of wavefield sampling. A
uniform grid or series of lines is much like a tree farm with trees
neatly laid out in rows with a common, but close spacing of each
tree within a row. The gaps between the trees represent gaps in
seismic data that are literally large enough to drive a tractor
through it. We don't know what is in the gaps and since they extend
so far, there may be something fairly large. However, where the
trees are lined up, the seismic data is oversampled as a recorder
may actually be turned off and the two adjacent receivers will
almost certainly provide sufficient data to accurately predict what
the silent recorder would have captured. What should be disturbing
is that the gaps are not just between two rows, but there are gaps
running at 45 degree angles and 90 degree angles to the rows.
Consider the views within Arlington National Cemetery where one is
seeing all of the headstones that are perfectly aligned. Many
headstones are somewhat hidden by the perfect alignment in quite a
few orientations. This arrangement of headstones is good for
demonstrating military precision and honoring fallen soldiers, but
not as good for getting as much information about the geologic
subsurface with the receivers available. While a random arrangement
of receivers or sources is not desired, the point of a desired
non-uniform arrangement may be visualized while standing in the
middle of a dense forest where one has the impression of seeing an
impenetrable array of trees. From any location, there are enough
trees in view to be seen in a composite as an impenetrable forest.
In a tree farm that may actually have more trees than the forest
allows long views that are wide enough for tractors to easily
drive. The rows of trees make the hidden trees seem redundant.
[0025] The critical question is how variable can we space the lines
and stations and still recover our wavefield accurately. With
knowledge of the likely complexity of the subsurface, synthetic
surveys may be constructed and run on computers using varying
arrays of receivers and sources. Using the data acquired by the
synthetic survey, a wavefield reconstruction is created and
compared to the underlying model. A variety of such tests will
provide guidance to designing the various spacings in the actual
survey. Clearly, a sparser survey is a less expensive survey and if
accuracy can be obtained at lower cost, then a sparser survey will
be undertaken that will provide the accuracy or precision
needed.
[0026] Essentially, geophysicists are able to process and interpret
seismic data to map the various interfaces between formations based
on individual data points established by the time delay of the
signal returned from the formation. The data actually forms a large
plurality of interface points. The points may be seen to form a
nearly continuous line along each of the interfaces in the
direction of the vessel travel. Closely spaced "lines" of receivers
provides higher three dimensional definition, but at considerably
higher cost. Simply put, it takes a certain amount of time to
deploy a line of seismic receivers and recover it from the field.
Therefore, close lateral spacing of receiver lines means more labor
cost and time performing the survey. While it would be preferred to
properly sample the wavefield containing the echo returns with
close spacing of lines and receivers, the costs associated with
such a proper survey can be very costly to cost prohibitive.
[0027] Currently, geoscientists interpolate the shape of the
geological interfaces in the gaps between points by using the data
received by seismic receivers that are close to the gaps in
question. Most interpolation algorithms are simple mathematical
processes, such as basic averaging of the nearby data. With the
missing information supplied by the interpolation, the data is
provided to seismic processors to create an image of the geological
subsurface. However, according to the present invention, it is
better to reconstruct the entire wavefield in one realization.
Wavefield reconstruction involves statistical linear regression
analysis where a model wavefield is created from prior knowledge of
the geological subsurface and is iteratively refined based on
actual measured data from the seismic survey. Through the
regression analysis, the L0 and L1 norms are calculated for each
comparison between the model wavefield and the actual data such
that the model wavefield is iteratively corrected until calculated
L0 and L1 norms are minimized. At L0 and L1 norm minimization, the
model wavefield is believed to most accurately represent the actual
wavefield that would have ascended from the geological subsurface
if data could have been recorded at every possible location. Thus,
at this point, the model wavefield or reconstructed wavefield may
provide data from the entire surveyed area including all gaps
between points and from any point or points within the survey area.
Data from the reconstructed wavefield is then processed in the
conventional manner to create a three dimensional image of the
subsurface structures. With an accurately reconstructed wavefield,
the shape of the geological interfaces can be more properly imaged.
It should be recognized that wavefield reconstruction utilizes data
from receivers well distant from gaps as the iterative process
attempts to "fit" the model wavefield to the larger data set.
Wavefield reconstruction algorithms model the wavefield based upon
its components and the physical properties of the survey area being
sampled. In the present invention, prior knowledge of the
geological substructures in the design of the receiver array and
especially the non-uniform spacing of the receiver array enhances
and enlarges the strength of such algorithms to obtain a more
accurate reconstructed wavefield with the same number or fewer data
points. Wavefield reconstruction also takes advantage of the truism
that the simplest model of the earth that accurately fits the
measured data is likely the most correct model. Thus, by minimizing
the L0 and L1 norms, the complexity of the geologic model that
accurately matches the measured data is also minimized and provides
a very useful reconstructed wavefield for imaging.
[0028] The wavefield reconstruction fidelity is dependent on the
receiver spacings used in the sampling of the wavefield. It has
been found that the wavefield sensed in the lateral dimension
(perpendicular to the line of receivers) by the receivers can be
better reconstructed if the receivers are spaced in a non-uniform
or irregular spacing. The estimation can typically be quite
accurate depending on the complexity of the geological interface. A
flat interface is quite easy.
[0029] Consider the situation where someone desires to determine
the contour of the bottom of a back yard pond where the water is
dark and the person does not want to get wet. Since we know before
hand that a pool normally has a generally flat or rounded bottom
with some small variation in depth from one end to the other and
that the deepest points will be away from the edges and somewhere
centered within the pool, we can use this knowledge to take some
short cuts. Using this knowledge, we can determine that a solution
would be to take a yard stick and dip it into the pond at various
places in the pond and develop a rough, but fairly accurate model
of the bottom of the pond. This use of prior knowledge of the
general type and nature of the pool allows us to model the problem
and determine a method that would sample less densely and just a
few profiles allow us to determine a very accurate representation
of the pool bottom.
[0030] Next, let us consider what would happen if the pool is now a
murky fishing pond. Now we can not make the assumption that the
pool bottom is flat or smooth in fact more then likely the bottom
is quite rough with rocks logs and other trash. If we look around
the area on the surface we might conclude the bottom could have
logs, brush or rocks. In this case, if the bottom is a very rough
surface or unpredictable surface, the contour of the bottom is much
more complicated and challenging to survey with few samples. Now a
more densely sampled survey with more sampling profiles would be
needed to accurately measure the subsurface. This kind of
complication routinely occurs in seismic surveys.
[0031] The present invention uses some relatively simple logic to
provide quality subsurface maps, models or images of geological
interfaces, but creates such maps, models or images from data that
can be acquired in a more efficient manner than current techniques
using interpolation methods that are currently available. Returning
to the backyard fishing pond example, the present invention would
be practiced in a very small scale but analogous example where the
surveyor would make several depth measurements fairly close
together to determine how smooth or continuous the bottom is. The
surveyor would then combine this knowledge with a review of the
observations from the surface and determine the likelihood of
debris and logs or rocks in the pond. If the bottom were to be
smooth or flat, then the remainder of the measurements may be few
and spread out. The depth between actual measurements may be
confidently interpolated. For example, the depth at a point half
way between two actual measurements two feet apart that are 16
inches and 18 inches may be confidently interpolated to be 17
inches. One need NOT make the actual measurement, especially if the
time or cost to make such measurement is substantial. On the other
hand, an efficient survey design could be developed that would
provide a reasonably accurate model of a more complicated bottom
structure, but the measurements would be closer together. The
critical difference is between the concepts of interpolation and
reconstruction. Interpolation is a mathematical process that does
not use prior knowledge of what is being sampled to calculate the
new value. In our example, most algorithms will come up with 17
inches regardless of the subsurface because that is the average of
the two measurements. Interpolation takes no account of the prior
knowledge of what is being sampled. This works with a pool bottom
that is smoothly varying but if we consider a rough bottom of
brush, rocks and logs, then we cannot confidently interpolate the
answer. In this case we must reconstruct the bottom through using
prior knowledge of the likeliness of the roughness on the bottom
and proper sampling of the data we do sample.
[0032] Back to a seismic survey, applying the aforementioned
concept becomes much more complicated for seismic data acquisition
in that portions of the survey area may be simpler geological
structures and other portions may have more complicated structures.
Typically, a seismic data survey will survey an area where some
data has already been collected, but the data is not sufficiently
rich to resolve potential hydrocarbon deposits for drilling. This
data from prior surveys maybe sparse 3D or 2D seismic data or even
from well logs or other geological observations. Data from prior
surveys may provide enough information to determine the complexity
of the geological structures and create models of the substructures
sufficient to analyze the "spacing" of actual data necessary to get
a sufficiently accurate image of the geological substructures that
are sufficient to justify the risk for spending millions of dollars
on exploration wells. So, this invention is about getting
sufficient volumes or density of seismic data to decide and plan a
drilling program while minimizing the cost of gathering the seismic
data.
[0033] Referring now to FIG. 2, a seismic data acquisition system
is indicated by the arrow 20 where eight receiver lines comparable
to the eight receiver lines of FIG. 1. However, the receiver lines
25A, 25B, 25C, 25D, 25E, 25F, 25G and 25H are arranged to be spaced
from one another by an uncommon or irregular spacing. Along each
receiver line are a number of generally evenly spaced seismic
receivers 27. As deployed for seismic data collection in FIG. 2,
the total system width S.sub.2, is wider than S.sub.1. As with
system 10 in FIG. 1, each pair of receiver lines have an individual
receiver line spacing indicated as 29.sub.ab, 29.sub.bc, 29.sub.cd,
29.sub.de, 29.sub.ef, 29.sub.fg and 29.sub.gh. While one or more
receiver line spacings may be the same as other receiver line
spacings, not all are the same. Preferably, at least one receiver
line spacing 29 is equal to or less that the receiver line spacing
19 of the system 10 shown in FIG. 1. Specifically, spacing
29.sub.ed is the same as spacing 19.sub.ed while spacing 19.sub.ab
is slightly larger than spacing 19.sub.ab and spacing 29.sub.bc is
quite a bit larger than spacing 19.sub.bc. At least one receiver
line spacing must be less than or equal to or very close to equal
to the receiver line spacing 19 of the System 10 in FIG. 1 in order
to provide the accuracy of the data collected by inventive system
20. Since S.sub.2 is wider than S.sub.1, the area to be surveyed
will be surveyed in less time at lower cost with an inventive
system 20 configuration as compared to a conventional system 10
configuration as the survey area will be covered by fewer receiver
lines overall. The range at which a configuration may be made wider
without losing comparable accuracy depends on the complexity of the
subsurface structures in the area to be surveyed. Based upon
current studies, comparable accuracy may be obtained with S.sub.2
being 10 to 20 percent wider and current estimates are that 35%
wider provides data that is accurately processible. The same
current analysis indicates that above 35% may create unacceptable
holes in the data in certain complex substructures, but upwards of
50% and as high as 90% is possible and likely in fairly simple
geologic structures and in seismically benign areas.
[0034] Turning now to FIG. 3, the inventive technique of the
present invention may be used to another and perhaps opposite end.
The first end was to create an accurate model of the geological
substructures with a sparser array of receiver lines. The opposite
end is to provide a much more precise model of the geological
substructures without giving up productivity. In FIG. 3, a system
30 is shown where eight receiver lines comparable to the eight
receiver lines of FIG. 1 and of FIG. 2. Like system 20, the
receiver lines 35A, 35B, 35C, 35D, 35E, 35F, 35G and 35H are
arranged to be spaced from one another and by an uncommon or
irregular spacing. However, the lateral width S.sub.3 of system 30
is approximately the same as S.sub.1, the width of conventional
system 10. Along each receiver line is a number of generally evenly
spaced seismic receivers 37. Like in System 10 in FIG. 1, each pair
of receiver lines have an individual receiver line spacing
indicated as 39.sub.ab, 39.sub.bc, 39.sub.cd, 39.sub.de, 39.sub.ef,
39.sub.fg and 39.sub.gh. While one or more receiver line spacings
may be the same as other receiver line spacings, not all are the
same. Preferably, at least one receiver line spacing 39 is less
that the receiver line spacing 19 of system 10 shown in FIG. 1
while one or more receiver line spacings 39 are larger than the
common receiver line spacing 19. However, since S.sub.3 is
essentially the same as S.sub.1, the area to be surveyed will take
about the same number of receiver lines and about the same amount
of time with the inventive system 30 configuration as compared to
the conventional system 10 configuration. What is key is that
having one or two or three receiver line spacings 39 being less
than the common receiver line spacing 19 provides greater wavefield
reconstruction accuracy. The closely spaced receiver line spacings
39.sub.ab and 39.sub.ef provide accurate data and provide details
for the wavefield reconstruction algorithms and processors to more
accurately estimate the shape of the geological interfaces in the
larger gaps represented by spacings 39.sub.bc and 39.sub.de. System
30 essentially provides higher detail without higher cost.
[0035] In other more preferred embodiments, the receivers
themselves do not have to be equally spaced along the receiver
lines. As shown in FIGS. 4 and 5, the receiver lines are unequally
spaced in the same manner and spacing as system 20 in FIG. 2. In
FIG. 4, the system 40 the spacing of the receivers along a receiver
line is shown to be non-uniform. It should be seen that all of the
receiver lines have the same common, but unequal spacing. Thus, the
receivers are all in common lines or straight columns from top to
bottom of the drawing. In FIG. 5, the system 50 has the same
non-uniform receiver line spacing as system 20 in FIG. 2, but the
spacing of the receivers along the receiver line is not only
non-uniform, but not the same from receiver line to receiver line.
In other words, the receivers do not line up in straight
columns.
[0036] In FIG. 6, the system 60 does not include alignment in any
direction and are two dimensionally non-uniform. It should be noted
that the sources through all of the embodiments from system 20 to
system 60 include sources that have been maintained in common
regular spacing. Referring to FIG. 7, the system 70 at first
appears to be exactly the same as system 20. All of the receivers
are aligned and ordered in the same common spacing. However, a
closer inspection reveals that the center column of sources are
closer to the left column and further from the right column.
Essentially, system 70 shows that the sources may also be arranged
in the non-uniform arrangements of the receivers.
[0037] Referring to FIG. 8, the next level of complication of
source spacing is demonstrated by system 80 which includes varied
spacing vertically, but all columns have the same non-uniform
spacing.
[0038] Referring to FIG. 9, system 90 shows a slightly more
complicated arrangement for the sources where they remain in
straight columns, but the columns are non-uniformly spaced, the
spacing vertically within the columns is no-uniform and each column
is differently non-uniformly spaced.
[0039] System 100 in FIG. 10 shows an additional bit of complexity
where the sources are fully varied in both vertically and
horizontally in the Figure, but on the ground in both the x and y
directions.
[0040] What should be recognized in systems 70 through 100 is that
the receivers have all be uniform in both directions. Many
combinations of non-uniform spacings for both the sources and
receivers are possible. The permutations of a few combinations of
spacings for both sources and receivers have been described above.
The most complicated combination is shown in FIG. 11 where system
110 includes the sources have full two dimensional non-uniformity
and the receivers being fully non-uniform in two dimensions. The
following table suggests that more combinations are possible and is
presented to avoid presenting many extra drawings that are
unnecessary to the understanding of the present invention:
TABLE-US-00001 FIGURE Source Receiver Prior Art Uniform Uniform
FIG. 1 FIG. 2- Uniform Non-Uniform LINES wider with uniform spacing
along lines FIG. 3- Uniform Non-Uniform LINES high with uniform
spacing definition along lines FIG. 4 Uniform Non-Uniform LINES
with REGULAR Non-Uniform spacing along lines FIG. 5 Uniform
Non-Uniform LINES with Irregular Non-Uniform spacing along lines
FIG. 6 Uniform Non-Uniform in 2D FIG. 7 Non-Uniform LINES with
Uniform uniform spacing along lines Non-Uniform LINES with
Non-Uniform LINES uniform spacing along lines with uniform spacing
along lines Non-Uniform LINES with Non-Uniform LINES uniform
spacing along lines with REGULAR Non-Uniform spacing along lines
Non-Uniform LINES with Non-Uniform LINES uniform spacing along
lines with Irregular Non-Uniform spacing along lines Non-Uniform
LINES with Non-Uniform in 2D uniform spacing along lines FIG. 8
Non-Uniform LINES with Uniform REGULAR Non-Uniform spacing along
lines Non-Uniform LINES with Non-Uniform LINES REGULAR Non-Uniform
with uniform spacing spacing along lines along lines Non-Uniform
LINES with Non-Uniform LINES REGULAR Non-Uniform with REGULAR
spacing along lines Non-Uniform spacing along lines Non-Uniform
LINES with Non-Uniform LINES REGULAR Non-Uniform with IRRegular
spacing along lines Non-Uniform spacing along lines Non-Uniform
LINES with Non-Uniform in 2D REGULAR Non-Uniform spacing along
lines FIG. 9 Non-Uniform LINES with Uniform Irregular Non-Uniform
spacing along lines Non-Uniform LINES with Non-Uniform LINES
Irregular Non-Uniform with uniform spacing spacing along lines
along lines Non-Uniform LINES with Non-Uniform LINES Irregular
Non-Uniform with REGULAR spacing along lines Non-Uniform spacing
along lines Non-Uniform LINES with Non-Uniform LINES Irregular
Non-Uniform with Irregular spacing along lines Non-Uniform spacing
along lines Non-Uniform LINES with Non-Uniform in 2D Irregular
Non-Uniform spacing along lines FIG. 10 Non-Uniform in 2D Uniform
Non-Uniform in 2D Non-Uniform LINES with uniform spacing along
lines Non-Uniform in 2D Non-Uniform LINES with REGULAR Non-Uniform
spacing along lines Non-Uniform in 2D Non-Uniform LINES with
Irregular Non-Uniform spacing along lines FIG. 11 Non-Uniform in 2D
Non-Uniform in 2D
[0041] The ability to adequately reconstruct the wavefield will
then depend on the design of the source and receiver spacings in
both dimensions. Care must be taken in designing such a
configuration so that the wavefield does not become under sampled
for the subsurface objective being imaged. This can be modeled
prior to acquisition of the survey to determine the required
station and line spacing.
[0042] It should also be understood that receiver lines and source
lines may still be implanted with varying degrees of freedom, but
noting that there are no particular requirement that the
orientation of the source line and receiver lines be orthogonal for
the wavefield reconstruction to work. The lines may be oriented
with variations in direction, patterns or layout. Some of the more
common in the industry are the brick, zig-zag, slash and inline
survey designs. Non-uniform line and station spacing for wavefield
reconstruction work equally well with each of these survey
technique.
[0043] Finally, the scope of protection for this invention is not
limited by the description set out above, but is only limited by
the claims which follow. That scope of the invention is intended to
include all equivalents of the subject matter of the claims. Each
and every claim is incorporated into the specification as an
embodiment of the present invention. Thus, the claims are part of
the description and are a further description and are in addition
to the preferred embodiments of the present invention. The
discussion of any reference is not an admission that it is prior
art to the present invention, especially any reference that may
have a publication date after the priority date of this
application.
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