SYSTEM AND METHOD FOR DETERMINING A SET OF FIRST BREAKS OF A SEISMIC DATASET
20230184977 · 2023-06-15
Assignee
Inventors
Cpc classification
G01V1/345
PHYSICS
E21B49/00
FIXED CONSTRUCTIONS
International classification
G01V1/34
PHYSICS
E21B49/00
FIXED CONSTRUCTIONS
Abstract
A system and method for determining a set of first breaks of a seismic dataset are disclosed, the method including obtaining the seismic dataset composed of a plurality of seismic traces and a provisional first break for each seismic trace. The method further includes selecting a plurality of proximal picks for each seismic trace, determining a near-offset pick for each seismic trace starting with shortest offset and sequentially selecting traces in order of increasing offset, and determining a far-offset pick for each seismic trace starting with the farthest offset and sequentially selecting traces in order of decreasing offset. The method further includes determining a set of coincident picks based on the near-offset and the far-offset picks for each seismic trace, fitting a curve to the set of coincident picks, and determining the set of first breaks of the seismic dataset from the curve.
Claims
1. A method of determining a set of first breaks of a seismic dataset generated by a seismic source, comprising: obtaining the seismic dataset, wherein the seismic dataset comprises a plurality of seismic traces and a provisional first break for each of the plurality of seismic traces; selecting, using a computer processor, a plurality of proximal picks for each seismic trace, wherein each proximal pick lies within a time window enclosing the provisional first break; determining, using the computer processor, a near-offset pick fora seismic trace with a shortest offset and sequentially selecting, in order of increasing offset, a selected trace and determining the near-offset pick for the selected trace based on proximal picks of the selected trace and the near-offset pick for at least one seismic trace with a shorter offset than the selected trace; determining, using the computer processor, a far-offset pick for a seismic trace with a farthest offset and sequentially selecting, in order of decreasing offset, a selected trace and determining a far-offset pick for the selected trace based on the proximal picks of the selected trace and the far-offset pick for at least one seismic trace with a farther offset than the selected trace; determining, using the computer processor, a set of coincident picks based on the near-offset pick and the far-offset pick for each seismic trace; fitting, using the computer processor, a first break curve to the set of coincident picks; and determining, using the computer processor, the set of first breaks of the seismic dataset based, at least in part, on the first break curve.
2. The method of claim 1, wherein selecting a plurality of proximal picks for each seismic trace comprises: forming, using a computer processor, a positive trace from each of the plurality of seismic traces; determining, using the computer processor, a centroid time for each of a plurality of lobes of each positive trace; and selecting, using the computer processor, for each positive trace, the plurality of proximal picks, wherein each proximal pick comprises one centroid time lying within the time window enclosing the provisional first break.
3. The method of claim 1, wherein the set of first breaks of the seismic dataset comprises a first break for each seismic trace having a coincident near-offset pick and far-offset pick.
4. The method of claim 1, wherein the set of coincident picks comprises a coincident pick for each seismic trace for which the far-offset pick and the near-offset pick are identical.
5. The method of claim 1, wherein the plurality of proximal picks for each seismic trace comprises at least one proximal pick with a time less than a time of an initial first break for that seismic trace and at least one proximal pick with a time greater than the time of the provisional first break for that seismic trace.
6. The method of claim 1, further comprising: determining, using the computer processor, a seismic velocity model based, at least in part, on the set of first breaks of the seismic dataset; and determining, using the computer processor, a seismic image of a subsurface region of interest based, at least in part, on the seismic velocity model.
7. The method of claim 6, further comprising: planning a wellbore trajectory based, at least in part, on the seismic image; and drilling the wellbore trajectory.
8. A non-transitory computer readable medium storing instructions executable by a computer processor, with instructions comprising functionality for: receiving a seismic dataset generated by a seismic source, wherein the seismic dataset comprises a plurality of seismic traces and an initial first break for each of the plurality of seismic traces; selecting a plurality of proximal picks for each seismic trace, wherein each proximal pick lies within a time window enclosing the initial first break; determining a near-offset pick for a seismic trace with a shortest offset and sequentially selecting, in order of increasing offset, a selected trace and determining the near offset-pick for the selected trace based on proximal picks of the selected trace and the near-offset pick for at least one seismic trace with a shorter offset than the selected trace; determining, a far-offset pick for a seismic trace with a farthest offset and sequentially selecting, in order of decreasing offset, a selected trace and determining a far-offset pick for the selected trace based on the proximal picks of the selected trace and the far-offset pick for at least one seismic trace with a farther offset than the selected trace; determining a set of coincident picks based on the near-offset pick and the far offset pick for each seismic trace; fitting a first break curve to the set of coincident picks; and determining a set of first breaks of the seismic dataset based, at least in part, on the first break curve.
9. The non-transitory computer readable medium of claim 8, wherein selecting a plurality of proximal picks for each seismic trace comprises: forming a positive trace from each of the plurality of seismic traces; determining a centroid time for each of a plurality of lobes of each positive trace; and selecting, for each positive trace, the plurality of proximal picks, wherein each proximal pick comprises one centroid time lying within the time window enclosing a provisional first break.
10. The non-transitory computer readable medium of claim 8, wherein the set of first breaks of the seismic dataset comprises a first break for each seismic trace having a coincident near-offset pick and far-offset pick.
11. The non-transitory computer readable medium of claim 8, wherein the set of coincident picks comprises a coincident pick for each seismic trace for which the far-offset pick and the near-offset pick are identical.
12. The non-transitory computer readable medium of claim 8, wherein the plurality of proximal picks for each seismic trace comprises at least one proximal pick with a time less than a time of an initial first break for that seismic trace and at least one proximal pick with a time greater than the time of a provisional first break for that seismic trace.
13. The non-transitory computer readable medium of claim 8, wherein instructions further comprise functionality for: determining a seismic velocity model based, at least in part, on the set of first breaks of the seismic dataset; and determining a seismic image of a subsurface region of interest based, at least in part, on the seismic velocity model.
14. The non-transitory computer readable medium of claim 8, wherein instructions further comprise functionality for planning a wellbore trajectory based, at least in part, on the seismic image.
15. A system comprising: a seismic acquisition system; and a seismic processor configured to: receive a seismic dataset generated by a seismic source, wherein the seismic dataset comprises a plurality of seismic traces from the seismic acquisition system; determine an initial first break for each of the plurality of seismic traces; select a plurality of proximal picks for each seismic trace, wherein each proximal pick lies within a time window enclosing the initial first break; determine a near-offset pick for a seismic trace with a shortest offset and sequentially selecting, in order of increasing offset, a selected trace and determining the near offset-pick for the selected trace based on proximal picks of the selected trace and the near-offset pick for at least one seismic trace with a shorter offset than the selected trace; determine, a far-offset pick for a seismic trace with a farthest offset and sequentially selecting, in order of decreasing offset, a selected trace and determining a far-offset pick for the selected trace based on the proximal picks of the selected trace and the far-offset pick for at least one seismic trace with a farther offset than the selected trace; determine a set of coincident picks based on the near-offset pick and the far offset pick for each seismic trace; fit a first break curve to the set of coincident picks; and determine the set of first breaks of the seismic dataset based, at least in part, on the first break curve.
16. The system of claim 15, wherein selecting a plurality of proximal picks for each seismic trace comprises: forming a positive trace from each of the plurality of seismic traces; determining a centroid time for each of a plurality of lobes of each positive trace; and selecting for each positive trace, the plurality of proximal picks, wherein each proximal pick comprises one centroid time lying within the time window enclosing a provisional first break.
17. The system of claim 15, wherein the set of first breaks of the seismic dataset comprises a first break for each seismic trace having a coincident near-offset pick and far-offset pick.
18. The system of claim 15, wherein the set of coincident picks comprises a coincident pick for each seismic trace for which the far-offset pick and the near-offset pick are identical.
19. The system of claim 15, wherein the seismic processor is further configured to: determine a seismic velocity model based, at least in part, on the set of first breaks of the seismic dataset; and determine a seismic image of a subsurface region of interest based, at least in part, on the seismic velocity model.
20. The system of claim 15, wherein the seismic processor is further configured to plan a wellbore trajectory based, at least in part, on the seismic image.
Description
BRIEF DESCRIPTION OF DRAWINGS
[0008] Specific embodiments of the disclosed technology will now be described in detail with reference to the accompanying figures. Like elements in the various figures are denoted by like reference numerals for consistency.
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DETAILED DESCRIPTION
[0020] In the following detailed description of embodiments of the disclosure, numerous specific details are set forth in order to provide a more thorough understanding of the disclosure. However, it will be apparent to one of ordinary skill in the art that the disclosure may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.
[0021] Throughout the application, ordinal numbers (e.g., first, second, third, etc.) may be used as an adjective for an element (i.e., any noun in the application). The use of ordinal numbers is not to imply or create any particular ordering of the elements nor to limit any element to being only a single element unless expressly disclosed, such as using the terms “before”, “after”, “single”, and other such terminology. Rather, the use of ordinal numbers is to distinguish between the elements. By way of an example, a first element is distinct from a second element, and the first element may encompass more than one element and succeed (or precede) the second element in an ordering of elements.
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[0026] In accordance with one or more embodiments, the positive trace (306) includes only those portions of the seismic trace (300) with amplitudes greater than zero. Each continuous segment (“lobe”) of the positive trace (306) is shown as a black shaded lobe (308a-308q) on the positive trace (306). From each lobe (308a-308q), a centroid time, t.sub.c, may be computed, as:
where t.sub.s is the start time of the lobe, t.sub.e, is the end time of the lobe, u(t) is the amplitude of the positive trace, and w(t) is a weighting function.
[0027] In accordance with other embodiments, a centroid mask trace, C(t.sub.c.sup.i), may be calculated as:
where l.sup.i is the length of the i.sup.th lobe, and l.sup.avg is the average length of lobe in the positive trace. The center of each lobe, t.sub.c.sup.i, may be determined as:
t.sub.c.sup.i=t.sub.s.sup.i+(t.sub.e.sup.i−t.sub.s.sup.i)/2 Equation (3)
where t.sub.s.sup.i is the start time of the i.sup.th lobe and t.sub.e.sup.i is the end time of the i.sup.th lobe. The length of the i-th lobe, l.sup.i, may be determined as:
l.sup.i=t.sub.e.sup.i−t.sub.s.sup.i, Equation (4)
and the average length, l.sup.avg, of all the lobes in a trace as:
l.sup.avg=(Σ.sub.it.sub.e.sup.i−t.sub.s.sup.i)/i. Equation (5)
[0028]
[0029] In accordance with one or more embodiments, The proximal picks, (314a-f) may include a proximal pick, t.sub.1, (314c) that is the centroid time closest to the first break (312) in time that may be computed as:
t.sub.1=argmin(√{square root over ((t.sub.f−C(t).Math.t).sup.2)}), 0≤t≤t.sub.length Equation (6)
where c is the centroid time, t is time, and t.sub.length is the duration of the trace. Further, the proximal picks (314a-f) may include a proximal pick (314b) that is the centroid time closest in time, but earlier than, t.sub.1. This proximal pick time may be denoted t.sub.2 and may be computed as:
t.sub.2=argmin(√{square root over ((t.sub.1−C(t).Math.t).sup.2)}), 0≤t≤t.sub.1 Equation (7)
Further still, the proximal picks (314a-f) may include a proximal pick (314d) that is the centroid time closest in time, but later than, t.sub.1. This proximal pick time may be denoted t.sub.3 and may be computed as:
t.sub.3=argmin(√{square root over ((t.sub.1−C(t).Math.t).sup.2)}), t.sub.1≤t≤t.sub.length Equation (8)
Thus, a proximal pick array, denoted p.sub.2, may be computed as:
[0030] In accordance worth one or more embodiments the entries in the proximal pick array may be extended to include other centroid times (314a, b and 314e, f) that lie within the time window (310). A local extension algorithm may be used to extend the set of proximal picks. For example, if the value obtained from calculating proximal picks (314a-f) is non-zero, no additional proximal picks are added. However, if the value obtained from calculating proximal picks (314a-f) is zero but a continuous centroid time exists the continuous extension time may be chosen.
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[0034] The near-offset picks (502) and far-offset picks (504) are each determined such that the picks vary smoothly from one trace to the next. A near-offset may be determined from the proximal picks of a trace based, at least in part, on the value of near-offset picks (502) already determined for adjacent traces. For example, near-offset picks (502) and far-offset picks (504) may be determined based on the following algorithm:
TABLE-US-00001 Input:p(x, t) = 1 for sample with t = a proximal pick time; otherwise zero dt = time sampling rate of seismic data off(x) = offset information Output: l(x) = near-offset pick for each trace 1: x.sub.0 ← the spatial index of starting point 2: t.sub.0 ← the time index of starting point 3: n ← the number of traces 4: nt ← the number of time samplings 5: for x = 0 to x = n do 6: for t = 0 to t= nt do 7: if p(x, t) ≠ 0 then 8: for l = 0 to l = 20 do 9: v.sub.0 = off(x.sub.0)/(t.sub.0 .Math. dt) 10: v = off(x)/(t .Math. dt) 11: b.sub.x = |off(x) − off(x.sub.0)|/|(v + v.sub.0)/3. | 12: b.sub.t = dt 13: dist(l, t) = [{(x − l) − x.sub.0} .Math. b.sub.x].sup.2 + [{(t − t.sub.0)} .Math. b.sub.t].sup.2 14: end for 15: end if 16: end for 17: (l′ ,t′ ) = arg min dist(l, t) 18: x.sub.0 ← x − l′ 19: t.sub.0 ← t′ 20: l(x) ← t.sub.0 21: end for
Near-offset picks (502) may be determined iteratively from the nearest-offset trace to the far-offset trace. Far-offset picks (504) may be determined iteratively from the farthest-offset trace to the near-offset trace. It will be readily apparent to a person of ordinary skill in the art how to modify the above algorithm to determine far-offset picks (504) rather than near-offset picks (502).
[0035] Coincident picks (506) may be determined from near-offset picks (502) and far-offset picks (504). Coincident picks (506) are determined to exist where near-offset picks (502) and far-offset picks (504) coincide in time and offset.
[0036] In accordance with one or more embodiments,
[0037] In Step 604, in accordance with one or more embodiments, a positive trace for each of the plurality of seismic traces (300) is determined. In addition, a centroid time (314a-f, 316a-1) for each lobe (308a-q) of the positive trace (306) may be determined.
[0038] In accordance with one or more embodiments, in Step 606, a modified first break for each trace (300) beginning at a greatest active offset may be determined. Step 606 is described in greater detail below.
[0039] In Step 608, in accordance with one or more embodiments, the first of two stopping criteria may be evaluated. If the modified first breaks are all equal to the initial first breaks, then the flow may progress to Step 610. If the modified first breaks are not all equal to the initial first breaks, then the flow may progress to Step 614.
[0040] In Step 610, the second stopping criterion may be evaluated. If the shortest modified offset is the shortest offset (206) in the dataset (500), the workflow may terminate at Step 612. If the shortest modified offset is not the shortest offset (206) in the dataset (500), the workflow may progress to Step 618.
[0041] In Step 618, in accordance with one or more embodiments, a new greatest active offset equal to an offset between the smallest modified offset and the current greatest active offset is set, and each initial first break is set to be equal to each modified first break.
[0042] From Step 610, in accordance with one or more embodiments, if the shortest modified offset is not the minimum offset in the dataset, a new greatest active offset may be set. The new greatest active offset may be set equal to an offset intermediate between the shortest offset and the current greatest active offset. Further in Step 618, the initial first breaks may be updated to be equal to the modified first breaks and the workflow may proceed to Step 606.
[0043] If, in Step 608, the modified first breaks are not all equal to the initial first breaks, then the flow may progress to Step 614. If, in Step 614, all the modified first breaks are earlier than initial first breaks, the workflow may proceed to Step 614. However, if in Step 614, not all the modified first breaks are earlier than initial first breaks, the workflow may proceed to Step 616.
[0044] In Step 616, each initial first break may be set equal to the corresponding modified first break before the workflow proceeds to Step 606.
[0045]
[0046] In Step 704, near-offset picks (502) and far-offset picks (504) are determined, based, at least in part, on the plurality of proximal picks (314a-f) determined in Step 702. Near-offset picks (502) are selected in an iterative manner, beginning with the proximal picks for the positive trace (306) with the smallest offset, and proceeding by selecting near-offset picks for positive traces (306) with monotonically increasing offsets. In contrast, far-offset picks (504) are selected in an iterative manner, beginning with the proximal picks for the positive trace (306) with the largest offset, and proceeding by selecting far-offset picks for positive traces (306) with monotonically decreasing offsets. Each near-offset pick (502) is selected to minimize its separation in space and time from previously selected near-offset picks (502) in the iterative process. Each far-offset pick (504) is selected to minimize its separation in space and time from previously selected far-offset picks (504) in the iterative process.
[0047] In Step 706, in accordance with one or more embodiments, a set of coincident picks (506) are determined from the near-offset picks (502) and far-offset picks (504) is determined. Each coincident pick (506) is determined when the near-offset picks (502) and far-offset picks (504) coincide in time and offset.
[0048] In Step 708, in accordance with one or more embodiments, a curve is fitted to the set of coincident picks (506). The fitting may be performed using a method that is robust to the presence of outliers in the fitted coincident picks (506). The fitting may be performed using a random sampling consensus (“RANSAC”) method. Further, in Step 708, modified first breaks may be determined from the fitted curves for the offset of each positive trace lying between the coincident pick for the smallest offset positive trace and the coincident pick for the largest offset positive trace.
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[0053] The computer (1002) can serve in a role as a client, network component, a server, a database or other persistency, or any other component (or a combination of roles) of a computer system for performing the subject matter described in the instant disclosure. The illustrated computer (1002) is communicably coupled with a network (1030). In some implementations, one or more components of the computer (1002) may be configured to operate within environments, including cloud-computing-based, local, global, or other environment (or a combination of environments).
[0054] At a high level, the computer (1002) is an electronic computing device operable to receive, transmit, process, store, or manage data and information associated with the described subject matter. According to some implementations, the computer (1002) may also include or be communicably coupled with an application server, e-mail server, web server, caching server, streaming data server, business intelligence (BI) server, or other server (or a combination of servers).
[0055] The computer (1002) can receive requests over network (1030) from a client application (for example, executing on another computer (1002) and responding to the received requests by processing the said requests in an appropriate software application. In addition, requests may also be sent to the computer (1002) from internal users (for example, from a command console or by other appropriate access method), external or third-parties, other automated applications, as well as any other appropriate entities, individuals, systems, or computers.
[0056] Each of the components of the computer (1002) can communicate using a system bus (1003). In some implementations, any or all of the components of the computer (1002), both hardware or software (or a combination of hardware and software), may interface with each other or the interface (1004) (or a combination of both) over the system bus (1003) using an application programming interface (API) (1012) or a service layer (1013) (or a combination of the API (1012) and service layer (1013). The API (1012) may include specifications for routines, data structures, and object classes. The API (1012) may be either computer-language independent or dependent and refer to a complete interface, a single function, or even a set of APIs. The service layer (1013) provides software services to the computer (1002) or other components (whether or not illustrated) that are communicably coupled to the computer (1002). The functionality of the computer (1002) may be accessible for all service consumers using this service layer. Software services, such as those provided by the service layer (1013), provide reusable, defined business functionalities through a defined interface. For example, the interface may be software written in JAVA, C++, or other suitable language providing data in extensible markup language (XML) format or another suitable format. While illustrated as an integrated component of the computer (1002), alternative implementations may illustrate the API (1012) or the service layer (1013) as stand-alone components in relation to other components of the computer (1002) or other components (whether or not illustrated) that are communicably coupled to the computer (1002). Moreover, any or all parts of the API (1012) or the service layer (1013) may be implemented as child or sub-modules of another software module, enterprise application, or hardware module without departing from the scope of this disclosure.
[0057] The computer (1002) includes an interface (1004). Although illustrated as a single interface (1004) in
[0058] The computer (1002) includes at least one computer processor (1005). Although illustrated as a single computer processor (1005) in
[0059] The computer (1002) also includes a memory (1006) that holds data for the computer (1002) or other components (or a combination of both) that can be connected to the network (1030). For example, memory (1006) can be a database storing data consistent with this disclosure. Although illustrated as a single memory (1006) in
[0060] The application (1007) is an algorithmic software engine providing functionality according to particular needs, desires, or particular implementations of the computer (1002), particularly with respect to functionality described in this disclosure. For example, application (1007) can serve as one or more components, modules, applications, etc. Further, although illustrated as a single application (1007), the application (1007) may be implemented as multiple applications (1007) on the computer (1002). In addition, although illustrated as integral to the computer (1002), in alternative implementations, the application (1007) can be external to the computer (1002).
[0061] There may be any number of computers (1002) associated with, or external to, a computer system containing computer (1002), wherein each computer (1002) communicates over network (1030). Further, the term “client,” “user,” and other appropriate terminology may be used interchangeably as appropriate without departing from the scope of this disclosure. Moreover, this disclosure contemplates that many users may use one computer (1002), or that one user may use multiple computers (1002).
[0062] Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, any means-plus-function clauses are intended to cover the structures described herein as performing the recited function(s) and equivalents of those structures. Similarly, any step-plus-function clauses in the claims are intended to cover the acts described here as performing the recited function(s) and equivalents of those acts. It is the express intention of the applicant not to invoke 35 U.S.C. § 112(f) for any limitations of any of the claims herein, except for those in which the claim expressly uses the words “means for” or “step for” together with an associated function.