Key Drilling Technologies for Hot Dry Rock in Well HD-1R in the Hainan Fushan Sag

In order to explore the onshore thermal reservoir of the third member of Liushagang Formation and Changliu Formation in Paleogene Fushan Sag, Hainan Island, the first hot dry rock exploration well, Well HD-1R, was deployed in Huachang Block. A series of drilling problems occurred, including poor drillability of lower formation, difficulty in wellbore trajectory control, unpredictable coring recovery in deep formation, high formation temperature which affected drilling fluid stability and cementing quality, etc. In order to ensure the successful completion of Well HD-1R, the geological structure and lithological and physical characteristics of the area were analyzed, and then the BHA of the roller bit+ (Positive Displacement Motor)PDM and the high temperature-resistance downhole measurement instrument were applied to control the directional drilling trajectory. Based on the formation characteristics of coring section, optimized coring tools and drilling parameters were used to improve the core recovery rate. Then, high temperature potassium salt polymer drilling fluid was used to solve the problem of poor drilling fluid stability at high temperature, and a high temperature resistant double cementing slurry was adopted and targeted technical measures were taken to ensure cementing quality under high temperature environment. With the application of the above technical measures, the challenges caused by poor drillability of the formation and high formation temperature were overcome smoothly, thus ensuring the successful drilling of Well HD-1R. The successful completion of this well provided references and best practices for hot dry rock drilling in Hainan Island.