Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
1999-07-19
2001-12-04
McElheny, Jr., Donald E. (Department: 2862)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
C367S073000
Reexamination Certificate
active
06327537
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the analysis of seismic data and, more particularly, to data acquisition and processing systems and methods operable to supplement and/or optimize the analysis of seismic data.
2. Description of the Related Art
Hydrocarbon reservoirs are increasingly found in smaller traps in geologically complex areas, where they are not easy to identify or evaluate. The ability to simulate accurately and in real time seismic surveys by propagating elastic waves in complex inhomogeneous media can help improve the discovery rates and even the production of such reservoirs. Seismic surveying is a technique in which sound generated by a seismic (shot) source is received (and recorded) by a receiver or number of receivers after it has been reflected, refracted, or otherwise affected by geological structures within the body of the earth.
The problem of simulating seismic surveys corresponds to solving the differential equations which controls the wave propagation in the earth under a set of initial, final, and boundary conditions. The most successful numerical techniques for solving these differential equations include (i) finite difference methods based on numerical approximations of derivatives, (ii) ray tracing methods, (iii) reflectivity methods, and (iv) scattering methods based on Born or Kirchhoff approximations. These techniques differ by their regime of validity, their cost, and their usefulness in the development of interpretation tools like inversion. When an adequate discretization in space and time which permits an accurate computation of derivatives of the wave equation is possible, the finite difference technique is the most accurate tool for simulating elastic wave propagation through geologically complex models.
The use of finite difference modeling has risen dramatically in the past decade. The 1980s, the simulation of seismic surveys by finite-difference modeling was the domain of the academic, postdoctoral researcher or the similarly trained specialist with many years of grounding in the area. Recently, more and more engineers and interpreters in industry and even in the field operations are using the two-dimensional version of finite difference modeling to simulate seismic surveys. Their interest is motivated by the ability of finite-difference modeling to accurately model wave propagation through geologically complex ares. Moreover, it is very often easy to use. However, for finite difference modeling to become fully reliable for oil and gas exploration and production, three dimensional finite difference modeling cost-effective versions must be developed.
Three dimensional finite difference modeling has been a longstanding challenge for seismologists, in particular for petroleum seismologists because their needs are not limited to one simulation but thousands and thousands of simulations. Each simulation corresponds to a shot gather. Consider the simulations of elastic wave propagation through a complex geological discretized into 850×850×500 cells. The waveforms are received for 4000 timesteps. It has been estimated that it will take 10 years of computation time on Origin 2000 with 20 CPUs to produce a small three dimensional survey of 40,000 shots. That is why most three dimensional finite difference modeling has been limited to borehole studies (at the vicinity of the well) where the grid size is about 100 times smaller. One alternative to three dimensional finite difference modeling generally put forward by seismologists is the hybrid method where two modeling techniques (e.g., ray tracing and finite difference) are coupled together to improve the modeling accuracy or to reduce the computation time. For complex geological models containing significant lateral variations, this type of coupling is very difficult to perform or operate. Moreover, the connectivity of the wavefield from one modeling technique to another sometime produce significant amplitude error and even phase distortion in data obtained by the hybrid method.
The related art is represented by the following patents of interest.
U.S. Pat. No. 3,629,798, issued on Dec. 21, 1971 to Donald W. Rockwell, describes a method and system for refraction seismic exploration wherein detectors are provided for receiving refraction seismic signals generated from a first location and for subsequently receiving additional refraction seismic signals generated from a second location. Rockwell does not show or suggest a multi-shooting approach to seismic modeling and acquisition according to the claimed invention.
U.S. Pat. No. 4,319,347, issued on Mar. 9, 1982 to Carl H. Savit, describes a seismic system for the systematic surveying of extensive prospects which are responsive to significatly higher frequencies than systems which have been employed heretofore. Savit does not show or suggest a multi-shooting approach to seismic modeling and acquisition according to the claimed invention.
U.S. Pat. No. 4,486,866, issued on Dec. 4, 1984 to Francis Muir, describes a method of seismic exploration using non-impulsive vibratory sources activated by stationary, Gaussian codes. Muir '886 does not show or suggest a multi-shooting approach to seismic modeling and acquisition according to the claimed invention.
U.S. Pat. No. 4,598,391, issued on Jul. 1, 1986 to Francis Muir, describes a method of seismic exploration using non-impulsive vibratory sources activated by stationary, Gaussian codes in a wellbore environment. Muir '391 does not show or suggest a multi-shooting approach to seismic modeling and acquisition according to the claimed invention.
U.S. Pat. No. 4,601,022, issued on Jul. 15, 1986 to Francis Muir, describes a method of seismic exploration using non-impulsive vibratory sources activated by stationary, Gaussian codes in urban areas. Muir '022 does not show or suggest a multi-shooting approach to seismic modeling and acquisition according to the claimed invention.
U.S. Pat. No. 4,607,353, issued on Aug. 19, 1986 to Francis Muir, describes a method of seismic exploration using non-impulsive vibratory sources activated by filtered stationary, Gaussian codes. Muir '353 does not show or suggest a multi-shooting approach to seismic modeling and acquisition according to the claimed invention.
U.S. Pat. No. 4,780,859, issued on Oct. 25, 1988 to Mohamed T. Hadidi et al., describes a method to process seismic data to yield useful information regarding the subsurface area explored, wherein the acquired seismic data is autocorrelated and the amplitude spectrums are estimated, stacked, and averaged to reduce the effects of nonwhite reflectivity upon the data. Hadidi et al. do not show or suggest a multi-shooting approach to seismic modeling and acquisition according to the claimed invention.
U.S. Pat. No. 4,837,723, issued on Jun. 6, 1989 to Kenneth L. Peacock, describes a method and apparatus for continuous time-variant digital filtering of a digitized signal wherein the input digitized signal is separated into discrete windows. Peacock does not show or suggest a multi-shooting approach to seismic modeling and acquisition according to the claimed invention.
U.S. Pat. No. 4,852,068, issued on Jul. 25, 1989 to Antoine Track, describes a method of seismic exploration by filtering a two-dimensional signal g(z,t) built up from a set of signals g
i
(t) for 1<i<n as produced by at least one seismic wave detector placed at different depths Z
1
, . . . ,Z
i
, . . . ,Z
n
in a borehole. Track does not show or suggest a multi-shooting approach to seismic modeling and acquisition according to the claimed invention.
U.S. Pat. No. 4,860,265, issued on Aug. 22, 1989 to Stanley J. Laster et al., describes a method of using f-k filtering to restore coherent events to missing traces in seismic data such that the restored trace is consistent with coherent events in the vicinity of the restored trace. Laster et al. do not show or suggest a multi-shooting approach to seismic modeling and acquisition according to the claimed invention.
Litman Richard C.
McElheny Jr. Donald E.
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