Induced micro-seismicity during well discharge: OW-719, Olkaria, Kenya rift

A micro-seismic survey was carried out in concurrence with reservoir interference tests around Olkaria well 719, which has a mass output of 140±160 ton/h. The correlation between output and micro-seismicity shows that the seismic intensity peaks have a time lag of 6 to 11 days behind the mass output peaks. Seismicity spreads from the well bore in two major directions, a faster NE±SW trend at about 0.6 m/h and a slow NW±SE trend at about 0.4 m/h. These rates are comparable to those obtained by injecting organic tracers and monitoring in adjacent wells. Fluid feeder zones are at 1300±1400 m and 1600±1800 m depth and are coincident with contacts between di€erent lithologies that provide capping and horizontal permeability. A possible NNE±SSW trending barrier to ¯uid ¯ow has been observed between OW-719 and OW-718 wells. # 1999 CNR. Published by Elsevier Science Ltd. All rights reserved.