Elasto-Plastic Analysis Of Casing Stress In Cyclic Stram Injection Wells

Heavy oil resource is an important part of the oil and gas resources in China, the proportion reached 20%- 25% of total resources. Technologies of heavy oil recovery mainly contain steam drive 、 steam stimulation and in-situ combustion,and steam stimulation is adopted the mostly in China. Casing damage problems in heavy oil thermal recovery wells seriously restrict the development of heavy oil exploitation at present, which cause great economic losses for oilfield production. In the process of steam injection, it will produce thermal stress in the casing, moreover steam injection cycle may also produce cycle residual stress, which will cause serious casing damage. It is great significance for steam injection well completion design and mining design to accurately predicting wellbore temperature field in the process of steam injection and casing heat load conditions, analysis of the production cycle of casing stress changes. Based on thermal recovery wells casing working condition of each production cycle, this paper carries out a study of thermal recovery wells casing stress analysis for the following several aspects:Combined with thermal recovery well production methods and wellbore structure characteristics of thermal recovery wells, established dangerous section temperature field mathematical model of thermal wells in a production cycle, the temperature rise of casing-cement-formation is clearly defined. The temperature field changes of casing dangerous section of thermal recovery wells is analyzed in the whole production cycle.Based on thermal elastic mechanics and the theory of thick wall cylinder in the uniform inside and outside pressure, the paper establishes the mechanical model of the combination composed of casing-cement-fornation ring, analysis the elastic chang of casing-cement-formation ring under elastic condition.Deduces the expression of stress and displacement of casing-cement-formation ring, and combined with the thermal recovery of in certain oilfield routine parameters discussed different injection-production cycle the stress distribution and yield of three different grade of steel casing.Elastic-plastic analysis model of the combination composed of wellbore-formation ring is establised to deduces the expression of stress and displacement of casing and cement ring in the Elastic-plastic zone by using the Tresca yield criterion. The expression of contact stress and bend radius of casing-cement-formation ring and the unrecoverable plastic deformation of casing and cement after a production cycle is also deduced, according to the displacement coordinate equation of the contact point of casing-cement ring and the equal stress conditions of the junction of casing elastic-plastic.Repeat the calculation process to get the casing safety production cycles.Finally,the elastic-plastic ananlysis of the wellbore-formation ring system is performed by using programming software(Visual Basic).The safety production cycle of casing of three different grade is also deduced combining with the production parameters of certain oilfield.