Experimental Study on High Strength Anti-H2S Gel Valves

When underbalanced drilling is carried out in Xinjiang Oilfield, the gel is eroded by rich H2S existed in the formation, and gel valves are severely affected by its working performance and life. In order to solve this problem, a series of studies were performed with high strength anti-H2S gel valves. At the simulated well temperature of 125℃, main polymers, organic crosslinking agents, ferric oxide (sulfide scavenger) and additives were selected in order, and optimized dosages to make up the gel. Experimental evaluation was performed on the basic performance of gel fluids, such as viscosity, gel strength, maximum sealing pressure and breaking capacity. Moreover, the effect of hydrogen sulfide on gel performance was evaluated by using anti-H2S evaluation apparatus. The results of evaluation showed that the viscosity of gel fluid was 50 mPa·s, the high-strength anti-H2S gel valve could be completely formed into gel at the temperature of 125℃ for 3.5 hours, and performance kept no change for 170 hours. Twenty four hours after gelling, the sealing pressure per meter of gel was 0.08 MPa, which could effectively resist 24 hours’ continuous invasion of 10000 mg/L H2S, and it may be broken completely within 60 minutes by adding the gel breaker with volume fraction of 10%. The research indicated that the high-strength anti-H2S gel valve had good performance in temperature resistance, wall stickiness and bearing strength, and it can meet the safety requirements for the underbalanced drilling in H2S-bearing formations.