Risk analysis method for drilling trouble in Northeast Sichuan

Northeast Sichuan is a representative gas field with high pressure, high production, and high hydrogen sulfide in China, and the complex geological structure and unpredictive drilling geologic environment bring uncertainty and risk for drilling design and operation. Based on the analysis of drilling trouble statistics, according to statistical decision method, the analysis model for drilling risk is established, and the drilling risk in Northeast Sichuan is analyzed. The results show that the accuracy of circulation loss model is 90.5238%; that of overflow model is 99.9855%; that of borehole collapse model is 99.802%; that of bit freezing model is 83.33%; and that of drill string failure model is 90%. Therefore, the analysis method for drilling risk is reliable, and meets with safety requirement of the drilling site, and it is significant theoretically and practically.