Geophysical inversion by iterative modeling involves fitting observations by adjusting model parameters. Both seismic and potential‐field model responses can be influenced by the adjustment of the parameters of the rock properties. The objective of this “cooperative inversion” is to obtain a model which is consistent with all available surface and borehole geophysical data. Although inversion of geophysical data is generally non‐unique and ambiguous, we can lessen the ambiguities by inverting all available surface and borehole data. This paper illustrates this concept with a case history in which surface seismic data, sonic logs, surface gravity data, and borehole gravity meter (BHGM) data are adequately modeled by using least‐squares inversion and a series of forward modeling steps.
Use of the borehole gravity (BHG) meter as a detector of density distribution suggests that a reservoir could be monitored for bulk density changes caused by redistribution of fluids after hydrocarbons have been partially extracted from it. In a simple situation in which liquid hydrocarbons are being extracted from a well, an overlying gas zone might begin to penetrate toward the perforations from above, while an underlying water‐zone formation might begin to penetrate toward the perforations from below. One idealized reservoir and one real reservoir are modeled for BHG meter responses in prepump and postpump reservoir conditions. Results suggest that the BHG meter density differences could be detected if the survey had a high degree of quality control.
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