Challenges Overcome and Lessons Learned: Knowledge Acumens from Drilling Geothermal Wells in Turkey

Abstract This paper provides an overview of the extensive geothermal drilling activities in Turkey. Based on the large-scale data obtained in Turkey, the study identifies and classifies the challenges and risks that have been faced during drilling according to the risk severity and repetition frequency. The main challenges that have been encountered can be grouped into several categories: formation/lithology, equipment requirements, excessive vibration levels, and high temperature. Due to the fractured nature of the metamorphic formations, partial or full losses have been faced frequently, which increases the possibility of stuck pipe issues. Directional control and the hole geometry are frequently affected by the strong formation dips, requiring extensive directional planning and detailed offset well analysis. Moreover, since the stratigraphy is interbedded with heterogeneous and hard formations that act like a "stinger", the bit choice and drilling parameter evaluation possess extra caution and necessitate point-by-point analysis. In addition, these formations are severely abrasive and require a high level of tool quality, especially coating-wise. Downhole drilling temperatures up to 180 degrees Celsius require service companies to utilize more durable seals, sensors, and materials. Extreme levels of vibrations and shocks above 100G may be faced during drilling, causing a lower rate of penetration. Results show that extensive off-set well analysis, utilization of vibration mitigation tools, cooling procedures, proper bit and directional equipment selection, and certain stuck pipe practices may minimize the risks involved while drilling geothermal wells, especially in metamorphic rocks.