Analysis of a Geothermal System Based on 3D Resistivity and Gravity Method


Gichira, J., Noor, Y.
Geothermal Development Company


ABSTRACT

With an estimated geothermal potential of 10,000 MWe, the Kenyan Rift section of the rift valley is a beehive of exploration activities. A closer look at Menengai, a new geothermal project under extensive exploration gives an insight of how to characterize a viable system. This study involved resistivity and potential field methods mainly gravity. Surface studies done in Menengai field have indicated a huge geothermal potential and has led to the drilling of several wells. The purpose of this study was to employ resistivity and gravity methods to understand the nature of Menengai field by developing resistivity and density structural models to characterize this geothermal system. The data used was sourced from Geothermal Development Company (GDC) and subjected to the necessary procedures before developing final models using WinGLink and, a program by golden software. For resistivity data, the outliers were removed then the data corrected for static shift followed by joint inversion and finally run through a 3D code. For gravity data, reduction procedures were done followed by trend surface analysis to separate regional from residual and finally specific filters applied to achieve the aim of this study. From this study, 3D resistivity models and gravity structural models were developed and the information used to characterize Menengai geothermal field as a high temperature field. Resistivity models were able to identify possible heat sources and outflow areas while gravity models identified permeability controls for Menengai geothermal field as follows: caldera rim faults that contribute mostly to deep vertical recharge, NNE-SSW faults along Solai graben, NNW-SSE faults along Molo axis, the southern fault extending towards Lake Nakuru and the uplifting dome in the central part of the caldera which enhance further fracturing within the caldera.

Key words: Geothermal, Resistivity, Potential.


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