Geothermal geology : stratigraphy and hydrothermal alteration of well OW-716, Olkaria geothermal area, Kenya

Abstract

The hydrothermal alteration mineralogy for well OW-716 was conducted with several different techniques. Results obtained from the alteration mineralogy indicate temperatures of less than 200 C within the first 500 m depth of the well, with an increase near the boiling curve going down to the well bottom, showing a temperature range in excess of 280 C. Similarly a preliminary fluid inclusion study carried out on the quartz crystals at a depth of 350 m showed temperatures of 180 C which is higher than both alteration and formation temperatures, while at a depth of 2260 m, lower temperatures in the range of 245 C were recorded indicating heating up within the reservoir. It is possible to correlate the lithological units of well OW-716 with the other neighbouring wells in the field, and the possibility of local structural controls could account for the losses in circulation experienced within wells OW-707 and OW-714. From the well subsurface geology, the upper part of the well has mostly tuffs and lava flows of a rhyolitic nature, then a succession of thin basaltic units, with tuff intercalations of various compositions; deeper below is mostly trachytes and rhyolite lava rocks with tuff intercalations