Key Drilling Technologies for Horizontal Wells with Ultra-Long Horizontal Sections in Nanchuan Shale Gas Field

The application of horizontal wells with ultra-long horizontal sections can improve the economic benefit of normal pressure shale gas in Nanchuan Shale Gas Field. However, there were many technical challenges with this technology, such as difficulties in predicting the ultimate extension capacity of horizontal sections and controlling wellbore trajectory, poor wellbore cleaning, large friction and torque, laborious casing running, frequent cementing leakage, and easy gas channeling, etc. Therefore, the pipe string mechanics and fluid mechanics were analyzed. Then, the force state of pipe strings during drilling and casing running in ultra-long horizontal sections was defined. Meanwhile, the hydraulic extension capacity of the ultra-long horizontal sections as well as the key influencing factors were analyzed. On the basis of the analysis results and drilling practices in Nanchuan Shale Gas Field, a group of key technologies were developed, such as wellbore trajectory optimization design, low-cost but efficient steering drilling, efficient wellbore cleaning, safe casing running, and foam cementing in ultra-long horizontal sections, etc. The above technologies were applied in two horizontal wells with horizontal section lengths exceeding 3 500 m. The whole drilling process was achieved by using drilling bits and positive displacement motors (PDMs) made in China as well as conventional logging while drilling (LWD). The average time for drilling and completion of the two wells was reduced by 25.4% compared with the design value, and the overall target frame of the actual drilling was controlled within 5 m. The encountering rate of high-quality shales and the compound drilling ratio in horizontal sections were above 90% and 90.45% on average, respectively. The maximum dogleg angle was 0.15°/30 m. It is not hard to see that the application of these technologies ensured efficient well construction while achieving increasing drilling speed and cost reduction. The key drilling technologies for horizontal wells with ultra-long horizontal sections in Nanchuan Shale Gas Field can provide a reference for speeding up the drilling of horizontal wells with a horizontal section length exceeding 3 500 m in China.