Study On Casing Collapse Resistance Under Complex Load Of Shale Gas Well

Shale gas is an important kind of unconventional natural gas,which has huge potential for reserves and production capacity in China.Fracturing is the key technology to realize the commercial exploitation of low permeability oil shale gas reservoirs.After a large-scale volume fracturing after cementing,the stress state of the casing will change.These conditions may not be taken into account when designing the casing and eventually lead to the collapse of the casing.This paper analyzes and studies the factors affecting the casing strength in the fracturing process of shale gas wells,and summarizes the calculation model of the casing's anti-squeezing ability under the relevant complex loads.The ABAQUS finite element software and laboratory's casing stress resistance experiment are used to simulate the complex casing working conditions and calculate the casing's anti-squeezing ability under the corresponding working conditions.A new calculation method is proposed for checking the anti-collapse strength of casing under complex loads to provide a reference for checking the anti-collapse strength of casing at the later stage,thereby ensuring the safety of shale gas casing in the production process.The main progress and research results are as follows:(1)Through the research and analysis of the main subsection fracturing technology and the fracturing construction process in China,the factors of the complicated loads in the casing fracturing process are clarified.And the reasons for the complicated loads produced by the wellbore in the fracturing are analyzed.(2)Using the hydraulic casing confining pressure device independently designed by the laboratory to simulate different working conditions of the casing in separate cases under the protection of the cement ring and not,such as non-uniform stress and casing eccentricity.The experimental results show that the maximum stress value of the casing under different working conditions can be used to summarize the change law of the casing's anti-squeezing ability,and to sum up the calculation model of the casing's anti-squeezing ability under the condition of complete cement ring and casing bending.(3)Using the ABAQUS finite element software to simulate the working conditions of the casing under complex loads,calculate the casing under the protection of the cement ring,under non-uniform stress,casing bending,casing eccentricity,lack of cement ring under the condition of anti-squeezing capacity,and using the calculated results to fit the calculation formula of the cocasing's anti-squeezing capacity under corresponding complex loads.(4)Calculate the anti-squeezing ability of casing under different working conditions by calculating the formula of casing anti-squeezing ability under complex loads,and propose a checking method for anti-squeezing strength of casing under the complex load of shale gas well.A typical field collapse casing is checked and analyzed,and relevant suggestions and measures are put forward.