Key Technologies Involved in Karstic Geothermal Reservoir Drilling in the Beijing-Tianjin-Hebei Region

Technical difficulties are encountered in the drilling of karstic geothermal reservoir in the Beijing-Tianjin-Hebei region. Lost circulation is frequent due to misjudgment of weathering crust, causing burial of drill bits induced by collapse; poor cementation of karstic geothermal reservoirs hinders core recovery; bedrock reservoirs present strong heterogeneity and poor drillability; bit selection requires much efforts and the rate of penetration (ROP) is low. Therefore, X-ray fluorescence (XRF) element logging has been used to accurately assess the weathering crust, so as to avoid lost circulation, and thus increase the well completion rate. The core recovery was improved by selecting JS-6 type fully-sealed pin-hanging multi-purpose coring barrel and an integrated core catcher, and the ROP was raised in bedrock reservoirs through optimal and customized design of bits based on the lithology and drillability of bedrock reservoirs. In order to solve the problems of sticking and lost circulation in the drilling process, corresponding technical measures were introduced, and finally the key technologies for karstic geothermal reservoir drilling in the Beijing-Tianjin-Hebei Region were developed. After applying these technologies, the well completion rate reaches 100% in the Beijing-Tianjin-Hebei Region. In addition, the drilling cycle is shortened by more than 10%, and the drilling cost is reduced by 12%. Research and practice showed that these key technologies can solve the problems of drilling in karstic geothermal reservoirs, and provide technical support for the exploration and development of geothermal resources in this region.