The first update for the SEG/EAEG 3-D Modeling Project appeared in the February issue of TLE and the March issue of First Break. Our goal is to design salt and overthrust 3-D models and then simulate realistic 3-D surveys based on those models. Given the project's significance and scope, we plan frequent progress reports. In conjunction with this goal and to solicit input, we have made recent presentations at SEG Cairo, the SEG/EAEG Summer Research Workshop in The Netherlands, the Stanford Exploration Project, and the Center for Wave-Phenomena at the Colorado School of Mines.The committee expects to freeze the models based on feedback from the SEG and EAEG membership. They will then be available to the general public, most probably via CD-ROM.We are soliciting commercial entities to be considered as the repository of the models and simulation results (perhaps one in Europe and one in North America). Progress reports of the project working groups (salt model, overthrust model, and computations and algorithms) follow. Salt ModelThe first version has been constructed and placed in the public domain, accessible via Internet, in GOCAD format. This version, primarily describing the model's structural components, measures 90 000 ft in x,y and 24 000 ft in z. Figure 1 shows a 3-D visualization of the major components.The velocities surrounding the salt body are typical of Gulf of Mexico sedseismic response and the computational iments and described by compaction cost of the synthetic generation. Prelimgradients based on K-V, curves (K, the inary results on a 2-D cross section gradient, varies spatially and V, is the using the spike technique have been obinitial velocity) and a geopressure surtained. Figure 3a shows the velocity face. However, a constant density conprofile and Figure 3b the resulting 2-D straint has been placed due to the finite zero offset simulation. These prelimidifference software employed and nary results seem to indicate that the available computational resources. This spike technique is adequate; however, constant density assumption and simple more testing is required. velocity gradient results in no seismicIn the meantime, a 3-D velocity grid, reflectivity in the sediments surroundemploying the spike technique, has ing the salt. Two techniques (Figure 2) been generated and provided to US Naare being investigated via 2-D finite diftional Laboratories for testing of the 3-D ference modeling. The first ("spike") finite-difference software. increases the velocity of the finite dif-A second area of considerable invesference grid cell nearest each layer tigation is how to perform 3-D finite boundary by a certain percentage. The difference simulation on the salt model second ("block") alternately increases within the current resources offered by and decreases the velocity of the K-V, the US Department of Energy. A first function for each successive layer. estimate on the required computing reSince these techniques can vary the seissources far exceeded the existing budmic response of the model, two-dimeng...
A time‐domain model has been developed for calculation of a synthetic vertical seismic profile (SVSP) from a sonic log recorded in a borehole. The SVSP has proven to be extremely useful in the interpretation of seismic data since it allows the interpreter to analyze the propagation of the source pulse through the earth in depth as well as time. Previously, the synthetic seismogram technique allowed analysis of the earth’s response to the source pulse at the surface only. However, the development of the SVSP allows insight into the entire wave propagation problem since the calculation shows the response of the earth to the source pulse at any depth point in the subsurface. For example, the synthetic seismogram can be used to identify an event on the seismic section as a multiple, whereas, the SVSP cannot only identify a multiple, but can also show which path the source pulse took through the earth layers to create the multiple. The SVSP can also be used to analyze the change in character of the source pulse due to the layering effect of the earth, for example, effects of a thin bed sequence; to study amplitude variations due to transmission losses; and to examine the effects of different source pulse bandwidths on the final surface seismogram, etc. As interpreters gain experience in analyzing the SVSP, many more applications are expected to appear.
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