Temperature and Pressure Distribution Analysis on Selected Geothermal Wells at Olkaria Using Completion and Heat Up Test Data

Abstract

Knowledge of the true temperature and pressure at every location within the formation and their variation across the field has many applications in resource definition, delineation, and power potential and even determines how a resource is exploited. For electricity generation, the rule of thumb is a cut-out temperature of 2300 C. Resources at lower temperatures can be used for power generation from binary plants (below 1800C) or for direct use applications. Temperature and pressure profiles over the wellbore length, particularly those taken after injection and during heating, find use in understanding feed zones in the well and those that are unlikely to be feed zones. Discharge tests directly indicate flow rates, and data from them tend to be more reliable for simulation purposes than data from injection tests. Ultimately complete understanding of a reservoir's temperature at a location was determined after thermal recovery is considered complete. The research uses data from newly drilled adjacent wells in Olkaria 1 and systematic analysis of the database containing pressure and temperature data collected by KenGen staff during completion and heating-up tests. A conceptual model was developed from the formation temperatures and pressure based on this analysis. Temperature and pressure distributions at various depths in each well were correlated with nearby wells to provide a clear understanding of the feed zone locations. The study concluded that the formation temperatures and pressure on geothermal wells were moderate, although slightly above the expected values. The study revealed a significant effect of limited entry length on pressure and temperature behaviours. The study highlighted a strong positive association between entry length and pressure, and moderate positive association between entry length and temperature. The study revealed that injection profile pressures were the highest.