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Cross Borehole Electromagnetic Induction for Reservoir Characterization

1992; Linguagem: Inglês

10.2118/23623-ms

Michael Wilt, H. F. Morrison, Aaron T. Becker, K. Lee,

Seismic Waves and Analysis

Abstract Audio-frequency cross-borehole electromagnetics (EM) is an interesting alternative to existing techniques for reservoir characterization. With this method signals may be propagated several hundreds of meters through typical sand/shale reservoirs and data may be collected at high accuracy with a high sensitivity to the subsurface resistivity. A vertical component, cross-borehole EM field system has been designed and built by Lawrence Livermore and Lawrence Berkeley laboratories for reservoir evaluation and monitoring. This system was deployed at the British Petroleum test facility in Devine, Texas for testing and the the UC Richmond field station facility for a saltwater monitoring experiment. The Devine site is in a region of simple, flatlying geology so that collected data could be unambiguously interpreted with layered models. The results of the test showed that crosshole EM profiles in wells spaced 100 meters apart data could be repeated in 24 hours to better than one percent and that the profile data could be fit to layered models within this same tolerance. The derived models showed a close correspondence with the borehole induction log. At the Richmond facility we injected 120,000 liters of 1-ohm-m saltwater into a shallow aquifer for the purpose of testing geophysical monitoring methods. Differences between cross-borehole EM profiles collected before and after the injection reveal a clear anomaly that can be attributed to the saltwater. Although the anomaly is of the proper dimensions and magnitude for the amount of saltwater its irregular shape has made it difficult to fit to our simple three dimensional prism models.