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

A micro-seismic survey was carried out in concurrence with reservoir interf erence tests around Olkaria well 719, which has a mass output of 140-160 to n/h. The correlation between output and micro-seismicity shows that the sei smic 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 fa ster 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 a nd monitoring in adjacent wells. Fluid feeder zones are at 1300-1400 m and 1600-1800 m depth and are coincident with contacts between different lithol ogies that provide capping and horizontal permeability. A possible NNE-SSW trending barrier to fluid flow has been observed between OW-719 and OW-718 wells. (C) 1999 CNR. Published by Elsevier Science Ltd. All rights reserved .