Optimization Design Method and Application of Nitrogen Horizontal Well Drilling Technology in Coalbed Methane Reservoirs

Due to characteristics such as low permeability, low pressure, low gas saturation, low water content, and high structural stress, Yuwang coalbed methane (CBM) is prone to issues such as well leakage, coal sensitivity to water, and coal fines blockage. Conventional drilling fluids can cause irreversible damage to the coal reservoir, whereas gas drilling can effectively protect it. In this study, nitrogen was used for drilling horizontal wells, and drilling operations were conducted in Yuwang Township, Fuyuan County, Qujing City, Yunnan Province. Directional test wells and horizontal production test wells were drilled. Using proprietary software, various construction parameters such as gas injection rate, injection pressure, torque under different conditions, and erosion and wear of the drill string were calculated, and the results were consistent with the actual geological conditions. In actual construction, the total length of the directional well was 882 m, and the total length of the horizontal well was 1019.59 m. The gas injection rate ranged from 90 to 120 m 3 /min, and the drilling pressure ranged from 20 to 40 kN. It is noteworthy that the mechanical drilling speed using nitrogen drilling was 11.64 m/h, approximately three times faster than conventional drilling. The stability of gas pressure during drilling in this experiment demonstrates the effectiveness of this technology in preventing well leakage accidents. Valuable experience in gas drilling and important considerations were obtained from this experiment, providing valuable insights for future applications.