Geothermal drilling fluids

Abstract

Geothermal well drilling is a vital part of a geothermal project after extensive surface scientific exploration and research have been done. Drilling is one of the most expensive activities of a geothermal project. In the drilling project, the circulation system takes up a part of the well cost. Making the selection of the geothermal well drilling fluid is vital to the success of the project. It is, therefore, important to select a drilling fluid that will provide the best results in terms of cost, safety, reaching the desired depth and the output of the well. Drilling fluids are required to remove cuttings from the well, cool and lubricate the bit and the drill string, and control the pressures during drilling. Various drilling fluids are selected in accordance to reservoir pressure, temperature and the drilling technique being utilized. Geothermal drilling fluids commonly used include water based mud, water only, aerated mud or water and foam. This report discusses the classifications of geothermal drilling fluids, their functions and properties, drilling fluid equipment and loss of circulation policy. The paper also discusses the environmental issues that come into play when using these fluids and a case history analysis of two wells, one from Iceland and another from Kenya.