Research On Casing Strength Calculation And Casing Damage Mechanics In Cyclic Steam Injection Wells

Heavy oil is an important part of petroleum resources.Technologies of heavy oilrecovery mainly contain steam drive、steam stimulation and in-situ combustion,and steamstimulation is adopted the mostly in China.Casing damage problems in Heavy oil thermalrecovery Wells seriously restrict the development of heavy oil exploitation atpresent,which cause great economic losses for oilfield production.It is of great urgency tosolve the problem of thermal recovery of heavy oil casing damage.On the basis of themain thermal recovery wells casing damage characteristics,this paper carries out a study ofcasing strength calculation method and casing damage mechanism in thermal recoverywells for the following several aspects:The temperature rise of the casing-cement is clearly defined by the simulationanalysis of thermal recovery wells wellbore temperature field at the end of steaminjection,combining the huff and puff production methods and wellbore structurecharacteristics of thermal recovery wells.Therefore, the environmental load of thermalrecovery wells casing in dangerous well sections is analyzed and the research model ofpresent study is simplified.Based on the theory of thick wall cylinder in the uniform inside and outside pressure,the paper establishes the mechanical model of the combination composed ofcasing-cement ring and the surrounding rock,analysis the elastic chang of casing-cementring under rigid formation,deduces the expression of contactstress of casing-cement ringand the pressure of surrounding rock and discusses three different grade of steel casingstress distribution in different injection-production cycle,combining with the thermalrecovery routine parameters of the liaohe oilfield.Elastic-plastic analysis model of the combination composed of casing-cement ringunder the condition of rigid formation is establised to deduces the expression of contactstress of casing-cement ring and the pressure of surrounding rock in the Elastic-plasticzone of the casing by using the Tresca yield criterion.The expression of contact stress ofcasing-cement ring and the pressure of surrounding rock when only the casing into plasticstate is also deduced, according to the displacement coordinate equation of the contactpoint of casing-cement ring and the equal stress conditions of the junction of casingelastic-plastic, which discusses the degree of plastic yield of casing in differentinjection-production cycle in perspective of the elastic-plastic analysis. The elastic-plastic analysis of the casing pipe N-80、P-105and P-110is performed byusing finite element analysis software(ANSYS).