Vertical seismic profiling-common midpoint gathers (VSP-CMP) by wavefield extrapolation

摘要

Direct arrivals from walkaway vertical seismic profiling or VSP survey data are used to derive Green's functions representing the seismic wave amplitude and travel time information required to extrapolate the vertical seismic profiling survey data from individual wellbore receivers to the individual source locations. The derived Green's functions are employed in a convolution process with upcoming primary wavefields from the VSP survey data for other surface locations. The derived Green's functions are also used in a correlation process with downgoing wavefields from the VSP survey data to extend lateral coverage of the VSP image. The sets of VSP-CMP gathers so formed are then processed to obtain information about the subsurface formations.

主权项

1. A computer implemented method of processing vertical seismic profiling survey data in the form of responses sensed by receivers in a wellbore to seismic energy travelling through subsurface earth formations from seismic sources deployed at individual source locations along a seismic line of profile extending on either side of the wellbore at surface locations on the earth to form vertical seismic profile common midpoint gathers for the surface source locations and obtain information about the subsurface earth formations, comprising the computer implemented processing steps of:
(a) assembling the vertical seismic profiling survey data in the computer to form records for the individual wellbore receivers of the responses of the subsurface earth formations to seismic energy in the form of:
(1) direct arrivals of seismic energy from the surface locations to the individual well bore receivers;(2) upgoing wavefields of the seismic energy from the surface locations; and(3) downgoing wavefields of the seismic energy from the surface locations; (b) deriving a Green's function for each individual source location in the vertical seismic profiling survey from the direct arrivals of seismic energy at the individual wellbore receivers from the sources at the source locations of the vertical seismic profiling survey; (c) the Green's function each individual source location representing a wave amplitude and travel time to extrapolate the vertical seismic profiling survey data from individual wellbore receivers to that individual source location; (d) convolving the derived Green's functions for each individual source location with the upgoing wavefields of the seismic energy emitted from the sources at the surface locations on an opposite side of the wellbore from the individual source surface locations to form a resultant convolved trace; (e) cross-correlating the derived Green's functions for each individual source location with the downgoing wavefields of the seismic energy emitted from the sources at the surface locations on the same side of the well as the individual source surface locations to extend lateral coverage of the vertical profiling survey; (f) assembling as seismic data gathers for the individual source surface locations the results of the processing steps of convolving and cross-correlating for the individual surface locations; (g) the assembled seismic data gathers forming vertical seismic profiling-common midpoint gathers for the individual surface locations of the responses of subsurface earth formations to the emitted seismic energy; (h) the vertical seismic profiling-common midpoint gathers forming for each of the individual source surface locations an extrapolated wavefield including the kinematic and dynamic effects of wavefield propagation at each such individual source surface location; (i) processing the formed vertical seismic profiling-common midpoint gathers for the source locations to generate a physical parameter of the subsurface earth formations; and (j) forming an output display of the generated physical parameter of the subsurface earth formations obtained from the processed vertical seismic profiling-common midpoint gathers.