Study On Formation Mechanism And Control Method Of Toxic And Harmful Gas In Longhupao Oilfield

Hydraulic fracturing is often used in new well reconstruction and old well stimulation,which is a very important stimulation measure in the process of oilfield development.However,during the flowback process of Longhupao oilfield after fracturing,toxic and harmful gas overflow was detected at the wellhead.It was found that more and more oil wells in the whole area produced toxic and harmful gas,which not only seriously threatened the life safety of fracturing workers in Longhupao Oilfield,worsened the construction environment,and forced the oilfield to stop fracturing construction,but also seriously affected the normal production of the oilfield.Aiming at the above problems,this paper first analyzed the geological situation,toxic and harmful gas production and the detection results of water,oil,gas and rock samples produced in Longhupao oilfield,and theoretically analyzed the possible causes of toxic and harmful gas production.On this basis,a large number of thermal cracking experiments of crude oil and fracturing fluid components were carried out.According to the experimental results,the formation mechanism and influencing factors were studied.The results showed that the crude oil of Longhupao oilfield can not produce hydrogen sulfide by pyrolysis at high temperature,but the aldehydes in the crude oil can produce carbon monoxide by decarbonylation,and the critical temperature is 75 ?;The components of fracturing fluid can not be cracked to produce hydrogen sulfide at high temperature,but potassium persulfate and sodium sulfite in fracturing fluid can react with crude oil to produce hydrogen sulfide by thermochemical reduction,and the critical temperature is 102 ?.Besides,the ability of potassium persulfate to produce hydrogen sulfide is stronger than that of sodium sulfite;The formation rocks have no obvious promoting effect on the gaes production;Part of the hydrogen sulfide produced in Longhupao oilfield was produced by sulfate reducing bacteria,which can produce hydrogen sulfide in the range of 20 ? to 70 ?,and 40 ? to 60 ? is the most suitable temperature for sulfate reducing bacteria to produce hydrogen sulfide.On the basis of the formation mechanism,the sulfur-free gel breaker and bactericide of fracturing fluid were explored;It is of great significance to ensure the normal production of Longhupao oilfield,and it can provide useful reference for solving similar problems in the development process of other oilfields.