Research On The Annulus Pressure Management Of High-sulfur Gas Wells

As the natural gas comsumption is increasing,the exploration of high sour gas reservoirs has been paid extensive attention.However,it is obvious that the development of high acid gas reservoir has brought great difficulties to the production of oil and gas wells,especially in high acid gas fields.And the sustained casing pressure(SCP)of gas well may cause unimaginable harm to the safety of wellbore and environmental safety.Aimed at the actual production conditions in the development of high sulfur gas fields,this paper systematically studies the annulus pressure and annulus corrosion management of gas wells,mainly including the following contents.Firstly,considering the influence of environmental factors on the corrosion of oil and gas wells,the effect of corrosion and environmental sensitive cracking on the integrity of wellbore for sour gas field was investigated using the electrochemical corrosion testing method.The electrochemical corrosion,galvanic corrosion and crevice corrosion test are carried out under high temperature high pressure(HTHP)and high sulfur content environment.The mechanism of galvanic corrosion and crevice corrosion between C110 casing and G3,17-4PH and 718 alloys and the corrosion severity are discussed.In order to provide a reliable basis for the management of annular corrosion,a set of evaluation methods and criteria influencing the corrosion and cracking of the wellbore in the sour gas field has been proposed for the environment containing complex gas-phase state of hydrogen sulfide,carbon dioxide,carbon dioxide,carbon dioxide,methane and water vapor.Secondly,based on casing environmental sensitive cracking theory and stress corrosion cracking test standard,the mechanical properties of casing were tested,including the metallography,hardness,strength and impact toughness.In order to obtain the stress corrosion cracking test method and characterization parameters for the sour gas field,the parameters of the fracture toughness and the resistance to stress corrosion in the simulated bottom hole corrosion environment are obtained.It is proved by experiments that the complicated corrosion conditions of hydrogen sulfide,carbon dioxide,methane and water vapor will not produce unacceptable corrosion and cracking tendency on the casing.At present,the annulus pressure value is lower than the allowable threshold value,and the natural gas phase state of wellhead annular space should be maintained to reduce the interference of deflation and recharge fluid to the well equilibrium state.Furthermore,based on the electrochemical corrosion mechanism of annular protective liquid,the effect of annular space medium injection with diesel,nitrogen with a small amount of annular protective liquid and nitrogen with a small amount of formation water on casing corrosion is investigated to evaluate the anticorrosion performance of annular protective liquid.The property of electrochemical corrosion and environment sensitive fracture in annulus protection fluid were evaluated at different temperatures using by corrosion weight loss test,galvanic corrosion test and crevice corrosion test.The annular corrosion management method was obtained.On the basis of the study of the uniform corrosion evaluation performance of the annular protective liquid,the possible local corrosion in the pipe of the gas well,such as crack corrosion and galvanic corrosion,should be paid more attention to provide more comprehensive information for evaluating the corrosion resistance of the annular protective liquid.Finally,the risk identification and classification of P1 well and the safety management method are established,and the results of wellbore integrity evaluation and the safety management methods for long term shut in are also obtained.The application practice shows that the annular space management control measures for HTHP gas well provide important support for the casing corrosion management in the sour gas field,thus ensuring the safety production of the gas well with SCP.