Comprehensive approach to torque and lost circulation problems in geothermal wells in terms of drilling fluid

摘要

Drilling in a lost circulation zone has long been a challenge in geothermal wells due to its strong potential for high torque and wellbore instability. Particularly in deviated, extended reach and horizontal wells, frictional forces between drill string and wellbore or casing may be high enough to interfere with running the pipe in and out of the hole. These forces may also increase the torque and the stress on drill string which may end up with severe problems like stuck pipe and lost in hole. High-temperature high-pressure (HTHP) drilling fluids design, which minimize loss rates and friction values, is critical for the success in the face of these challenging drilling practices. The goal of this research is to provide a solution-oriented approach to torque and lost circulation problems in potential seepage and partial loss zones in geothermal wells; by developing efficient water-based drilling fluid compositions. Non-aqueous fluids (NAFs) are known to have the highest lubricity performance. However, application of these drilling fluid systems is limited because of high cost and environmental constraints. Hence, water-based drilling fluids are good candidates for replacing conventional NAFs. This paper investigates water-based dril-ling fluid compositions with high lubricity performance, HTHP resistance and high loss zone plugging performance. The design and selection of HTHP drilling fluid system have been the focus of experimental studies and worldwide field experience. Several chemical commercial lubricants are added in this fluid system to find the compositions for the highest lubricity performance closest to NAF systems. Also, considering the formation characteristics, environmental constraints, reservoir contamination concern and drilling limitations; proper fluid compositions are formulated to plug the potential seepage and partial loss zones and reduce the differential-sticking tendency by using proper lost circulation materials and lubricants. This study aims to encourage the geothermal drilling industry worldwide, to utilize the developed drilling fluid compositions with enhanced lubricity and loss zone plugging performance together to overcome related major drilling problems. Results reveal that lubricity and pore plugging characteristics of the selected compositions are highly inno-vative and noteworthy to be used in field applications for geothermal drilling industry.