Occurrence State of Hydrogen Sulfide Invading into Wellbore during Drilling

There may be an accident or a disaster if we could not detect hydrogen sulfide(H2S)in a timely manner while drilling.Once pressure in the wellbore is not under control,hydrogen sulfide release to surface will cause property losses or even personnel safety accident.According to the engineering practices of Puguang gas reservoir in northeast Sichuan,this paper analyzed the physical and chemical effects after H2S invasion by numerical calculation,the influence of dissolution and chemical reaction between H2S and drilling fluid had been found.The analysis results showed that:after entering into wellbore,one part of H2S would rise to the top of the wellbore,the other part would have chemical reaction with and dissolve in drilling fluid;the solubility of H2S reduced with increase of temperature,and increased as the pressure rose;and the influence of pressure on its solubility was much larger than that of temperature.The concentration of H2S in the upper wellbore was much higher than the lower wellbore due to the effects of pressure and temperature.The drilling fluid pH value had a great impact on the absorption of H2S,since H2S reacted with drilling fluid.Measuring the concentration of S2- and H2S in the drilling fluid at the same time could detect H2S more accurately and in a more timely manner.