Presented: Geothermal Rising Conference 2024 – John Clegg, President and CTO, Hephae Energy Technology.
Read Published Paper.
ABSTRACT
Breaking the 200C Barrier: Development of an Integrated High Temperature Directional Drilling System.
So-called “unconventional” geothermal wells, also known as “EGS” (Enhanced Geothermal System) and “AGS” (Advanced Geothermal System) wells, are increasingly being funded and are starting to be drilled in large numbers. For understandable reasons, initial projects have been drilled at temperatures similar to those found in hotter oil and gas wells – initial EGS and AGS projects have been drilled at temperatures below 175C in order to take advantage of existing oil and gas drilling technologies that have been developed to operate under those conditions.
However, because unconventional geothermal wells are drilled for heat, not hydrocarbons, an arbitrary temperature limit based on what was an appropriate specification for a different industry makes no sense. This is particularly true because, as will be demonstrated in the paper, there is a strong correlation between temperature of the reservoir and economic performance of an asset.
Further, although we cannot yet be certain which of the many proposed designs for EGS and/or AGS will ultimately prevail, almost without exception the pilots being drilled and the projects being proposed rely for their performance on accurately drilled horizontal wells, often pairs or multiples of wells drilled closely together, sometimes at a given offset and sometimes even intersecting. This requires a high degree of accuracy and control when drilling and therefore strongly suggests that the technologies used for drilling horizontal and extended reach wells has a place in geothermal drilling – if only it could be made to work reliably at higher temperatures. Ideally the temperatures limits of those technologies could be increased to beyond 200ºC and ultimately as high as 300ºC.
Unfortunately, although the oil and gas industry has made great strides over the years in getting the operating temperature of downhole electronics from 120ºC to 175ºC, and, even on rare occasions, to 200ºC, the approaches taken in oil and gas tools do not lend themselves to getting to the even higher temperatures that unconventional geothermal will need.
This paper will describe a unique, blank sheet of paper, approach to the design and packaging of electronics and sensors, to create a brand-new tool that combines the functions of Measurement While Drilling (MWD) and Rotary Steerable Systems (RSS) and which will be able to break that 200ºC barrier.
It will describe the design decisions made and modelling done to ensure enhanced thermal performance without sacrificing any of the resistance to shock and vibration that oil and gas tools have acquired over the years – shock and vibration being significant in the hard, high friction basement formations that EGS and AGS will most likely inhabit.
It will show the results of thermal testing and lessons learned along the way and demonstrate the viability of a fully working integrated MWD/RSS system capable of operating in the previously “forbidden” region above 200ºC.