Casing Failure Under Non-Uniform In-Situ Stress And Analysis Of Repairing Tool

The failure law of different casings under different operating conditions are analyzed, the critical in-situ stress equations under different operating interior pressures and the chart of optimizing casings' types are achieved by way of the establishment of nonlinear FEM(finite element model). With the increment of minimum in-situ stress and the decreasing of critical in-situ stress coefficient, the distribution of interior critical stress of casings is different, and the change law is that the irregular shape tend to be a constricted ellipse, the shape of external load due to salt formation inclines to ellipse with the decreasing of critical in-situ stress coefficient, which is contrary to the direction of maximum and minimum in-situ stress. To prepare the early task during production, the critical in-situ stress equations under different operating interior pressure can be used to estimate the corresponding field-application roughly. Furthermore, the types of casings under different non-uniform in-situ stress can be optimized according to the chart of optimizing casings' types.The structure of the existed bulge offered by Zhongyuan Oil Field is optimized, and the results show that the radial expanding force offered by bulge can recover the failed casing, the sticking point is how much hydraulic pressure can hydraulic device on the ground afford. Based on the operation principle of bulge, nonlinear FEM to recover failed casing is built in this paper and the general results are: for the same kind of casing under the same operating interior pressure, the force of recovery increases regularly with the increment of thickness, especially for the thicker casing and the casing under higher operating interior pressure, the force of recovering is larger, and the requirement of bulge is more exigent. According to the data obtained in Zhongyuan Oil Field, ordinary casing can't bear such extremely high non-uniform in-situ stress, so special casing must be developed to the production of oil and water wells which are situated in gypsum-salt rock.