Research and application of the HTHS anti-H2S gel valve for underbalanced drilling

The results show that the gel viscosity is around 50 mPa · s before being pumped into well, meaning a good fluidity. Its sealing pressure is high enough to balance downhole pressure and resist invasion of 10,000 ppm H2S after gelation. In addition, the gel valve can be completely broken after adding 10% breaking agents for 60 min, meaning it can easily flow back and does not influence the subsequent normal operations. Field application shows that the gel valve had good sealing property, peak of total hydrocarbon in gas logging increased from 0 to 66.6% before and after the gel broken. The gel flowed out completely after it was broken and there was successful ignition at the well site. Thus, the HTHS anti-H2S gel valve can effectively meet the operational requirements, and is an alternative method to achieve the target of the whole process of UBD operations.