A borehole network consisting of five monitoring wells monitored the induced seismicity at a producing petroleum field for about 11months. Nearly 5400 microseismic events were analyzed and used to image the reservoir based on a new double-difference (DD) seismic tomography. The DD tomography method simultaneously solved for event locations and VP, VS, and VPVS models using absolute and differential P, S, and S-P arrival times. Microseismicity in the field was caused primarily by compaction of the reservoir in and above the gas-bearing formation and was distributed along the two major northeast-southwest faults in the field. The model resolution analysis based on the checkerboard test and the resolution matrix showed that the central part of the model was resolved relatively well for the depth range of 0.7to1.1km. Clear velocity contrasts were imaged across most parts of the two northeast-southwest faults. The VPVS ratio estimates from the tomographic inversion were low (<1.75) in the shallow depth range, likely caused by rock type and gas content; but they were large (>1.75) in the deeper part of the model, likely because of fluid-saturated formation. Thus, seismic tomography shows great potential for reservoir imaging and property estimation using induced seismicity.

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