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Abstract: High Resolution Electrical Imaging of a Reservoir During Production

DAILY, WILLIAM, Lawrence Livermore National Lab, Livermore, CA

Cross borehole electrical resistance tomography (ERT) has been performed in a reservoir undergoing steam flood in southern California. A baseline image, taken before steaming, shows the sequence of resistive sand and conductive shale and closely matches the induction log along the boreholes. Subsequently, for the past 15 months nine images have been made at regular intervals during steaming. Pixel by pixel differences between these and the baseline show changes in the formation electrical properties as a function of time with a spatial resolution between 5 and 10 feet.

The ERT images have been compared to temperature logs, steam injection data and production data. We conclude that the images show three effects: First, there are changes close to the boreholes appearing only very early in the time sequence. These features are believed to be short-lived transient effects of drilling fluids close to the hole. Second, there are small magnitude anomalies in the upper pay zone which we believe are natural formation fluids moving as a result of pressure changes from the steam flood. Third, there are larger magnitude anomalies in the lower part of the pay zone which are correlated with high temperature at the boreholes. We believe these anomalies are high temperature fluids-perhaps steam-moving in individual sand units.

AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California