Study On Interface Failure Mechanism Of Casing-cement Sheath In Thermal Recovery Well

There is a huge proven reserves of heavy oil around the world,the most effective method of heavy oil recovery in the world present is thermal production,the temperature of steam may up to 350 ?,during steam injection casing and cement sheath will be heated by steam in thermal recovery wells,high stress will be generated in casing and cement sheath due to the rising temperature,they will be damaged if the stress level exceeds the ultimate strength of them,due to the differences of thermal expansion properties in cement sheath and casing,the interface between them is prone to shear failure at high temperature,the damage of casing,cement sheath and the shear failure of interface between them will lead to the damage of first interface integrity,which will seriously threatens the normal production of thermal recovery wells.In this paper,the tensile test of TP100 H casing and N80 casing at 25? and 350? was carried out to obtain their mechanical parameters,the yield strength of the both casings decreased obviously at high temperature.Strength tests of two types of cement after curing for 7 days under 315? were carried out to obtain the mechanics property parameters of them.The cementing strength of the interface between casing and cement sheath was tested with a self-made test device.The stress of casing-cement sheath under high temperature was simulated by Abaqus based on the former test data,the simulation results show that the failure of the first interface below the packer is caused by shear failure and the deformation of casing and cement sheath,the failure of the first interface above the packer is caused by the slippage of casing and cement ring sheath.Therefore,it is recommended to use heat insulation tubing with good heat insulation performance for steam injection,high grade casing should be used below the packer to ensure safty production of thermal recovery wells.