Status and prospect of key drilling and completion technologies used in middle-deep natural gas fields of the Bohai Sea

The deep-seated oil and gas bearing structure in the southwest zone of Bozhong sag is the largest middle-deep natural gas field in the Bohai Bay and even in eastern China. To deal with the complex geological conditions, great reservoir depth, abnormal formation pressure and poor drillability in this area, the technical difficulties in the process of gas field development were analyzed from the aspects of abnormal pressure prediction, drilling efficiency, reservoir protection, comprehensive ROP (rate of penetration) improvement, borehole stability, wellbore safety and well control risk. Then, the key drilling and completion technologies that have been developed for the safe, environmental and efficient exploration and development of middle-deep natural gas in the Bohai Sea based on field practice in recent ten years were summarized systematically, including geology-engineering integrated fast evaluation, casing program optimization and safety control, middle-deep ROP improvement, high-temperature low-density drilling fluid and reservoir protection, and open hole DST in deep buried hill. With the further expansion of exploration field of middle-deep natural gas in the Bohai Sea, the geological characteristics will be more complex and the technical challenges will be more difficult. Finally, therefore, it was proposed to strengthen the research and development of the drilling and completion equipments, tools, materials and technologies for the development of middle-deep natural gas reservoirs with more complex geological conditions in the Bohai Sea and complete the offshore emergency rescue system, so as to guarantee the safety, environmental protection and efficiency of middle-deep gas well drilling in the Bohai Sea.