Application of micro-seismic methods to geothermal exploration : examples from the Kenya Rift

Abstract

Results from volcano-seismic studies of many geothermal fields show that they are possible resource-mapping tools for geothermal exploration and reservoir monitoring. They have been able to map the size and depth of possible shallow geothermal heat sources by analyzing data for seismic gaps, S-wave attenuation, reflected arrivals and converted waves. Analysis of shear wave split data for fracture density show high permeability areas that are potential targets for drilling high-producer wells. Variation of Vp/Vs ratios is related to reservoir fluid phases where low values are related to a decrease in P-wave velocity in the area with low pore pressure, high heat flow, fracturing and steam/gas saturation in the reservoir. High velocity ratios were found in the relatively liquid-saturated high-pressure fields that these ratios are useful tools for monitoring reservoirs under exploitation. The volcano-seismic approach can be useful as a stand alone tool for analyzing geothermal resource both at the exploration and exploitation stage that is cost effective in the long term