Research and application of the HTHS anti-H 2 S gel valve for underbalanced drilling

Nowadays the whole underbalanced status of the well during underbalanced drilling process needs to be realized to a great extent, and gel valve is helpful to achieve it. However, there is occasionally H2S in the formation during underbalanced drilling (Hereinafter abbreviated as UBD), which will seriously affect the performance and lifetime of gel valve. Thus, in this paper, a formula of high temperature high strength (HTHS) anti-H2S gel valve was developed based on the optimization of different additives, such as hydrolyzed polyacryamide (HPAM), organic crosslinking agents, sulfur removal agents, etc., which could withstand temperature up to 320 °F(160 °C). The gel valve was made by crosslinking reaction at high temperature to form strong chemical bonds of spatial network structure. With its own strength and adhesion to the casing wall after gelation, the gel valve could meet the requirements for sealing. The properties of the final formula were evaluated, including viscosity, temperature stability, anti-H2S performance, gel sealing pressure, gel strength gel breaking performance, etc. In addition, a new evaluation apparatus for high toxic H2S invasion was designed specifically.