Maintaining the Integrity of Geothermal Wells During the Construction Process

Abstract

Geothermal well construction activity has been accelerating considerably to assist in meeting the zero carbon emissions goal of many countries and industries by 2050. In some areas, the geothermal well construction methods are inherited from oil and gas wells, and the construction activity is carried out using the same equipment and similar processes and guidelines. This is particularly visible when it comes to well-control management. However, as more and more oilfield professionals enter the geothermal arena, it becomes essential to understand the differences between oil and gas and geothermal wells that heavily impact the construction of the geothermal well. There is an emerging need to differentiate between the oil and gas and geothermal well control and well integrity criteria required to drill conventional geothermal wells. Considering the broad range of geothermal well types and their associated flow conditions, the authors limited the discussion to conventional geothermal wells and, more specifically, to the geothermal wells drilled in volcanic fields. Common failures pertaining to well control that were recorded throughout the history of geothermal well drilling (starting circa the 1920s) revolve around the handling of thermal (steam) kicks. After careful investigation, the root causes of most of the steam kicks were found to be (i) engineering and crew incompetence and lack of specific experience, (ii) lack of targeted risk assessment, and (iii) lack of clear standard work instructions to be followed during routine drilling and well control operations. A clear need was then identified for a specific well control procedure and detailed drilling plan enhancements, which would also address the differences between well control operations during drilling hydrocarbon and geothermal wells. This paper lays out the basics of the preferred approach to maintain the geothermal well integrity by well control during its well construction process, intended to reduce risk and improve performance. It will also illustrate the main differences between geothermal and hydrocarbon well control during the well construction phase.