| Abstract |
Olkaria geothermal field under Kengen’s concession area is divided into 7 fields for easier resource management. These are Olkaria East, Central, Southeast, Northeast, Southwest, Northwest and Domes fields. Olkaria West field is under Orpower 4. The area under study occupies parts of Olkaria East and Southeast fields. It is bounded by coordinates 196000E & 200500E and 9900000N & 9903000N covering an area of approximately 15km2. The surface is covered by rhyolitic lava flows (Oloolbutot lava flow) and pyroclastics, the former being the younger unit. Several wells have been drilled in this area and the subsurface geology studied from drill cuttings obtained. The main lithological units are pyroclastics, rhyolites, tuffs, basalts, trachytes, syenitic and granitic intrusions. These intrusions are of importance in this study. Gravity survey has also been conducted and the gravity anomalies studied and compared with the subsurface rocks obtained during drilling for and correlation in their respective densities. It is evident that gravity is influenced by the rock’s porosity, saturation, mineralogy etc. The different rock units encountered therefore have different densities which can be determined by gravity measurements. For example, the densities of deep-seated rocks like intrusives generally have higher densities than the near-surface and loosely-consolidated rocks. This is because the intrusive rocks like granites are usually compact and have less porosity as compared to pyroclastics and shallow tuffs. This paper seeks to determine the extent of the intrusive rocks by correlating Bouguer anomalies form the gravity survey with the geological model formed from geology well logs. |