Research on flow of sour gas mixture in deep well annulus

Pressure control of oil and gas wells in high-sulfur natural gas reservoirs (well control) is critical in oil and gas drilling. Well control accidents have caused great losses of life and property. From 1960 to 1996, more than 1,120 blowout accidents occurred in the Gulf of Mexico and neighboring state capitals. Studying the principles of annulus flow with sour gas can help in early monitoring of overflow and provide theoretical guidance in actual drilling. Research of gas properties and phase behavior can reveal the reasons that sour gas is prone to blowout. The fluid flow principles of the annulus are analyzed with different contents of sour gas. In this study, a multiphase flow model of sour gas in the annulus is established based on sour gas solubility and critical parameters. The model is used to calculate and analyze the changes in sour gas properties and wellbore flow parameters with well depth. It was found that when high-content sour gas overflows, the gas expands violently near the wellhead, and the risk of blowout increases.