Analysis Of Anti-collapse Performance Of High Steel Grade Casing In Shale Gas Well

Casing collapse deformation in shale gas Wells is one of the most common problems in the development of shale gas,and its consequences will affect the stable and efficient exploitation of shale gas Wells.In order to deal with the problem of casing collapse and deformation under complex geological conditions,the oil industry has developed high steel grade casing for shale gas Wells with high yield strength and strong anti-collapse strength.Its performance is of great help to improve the safety of shale gas Wells during service.Based on the deformation of casing collapse risk as the research target,adopts the method of data analysis and simulation test,the analysis of the effect of casing defects on casing collapse deformation regularity and the effect size.And USES the reliability sensitivity analysis and the safety analysis method of combining the,get the deformation of casing collapse risk quantitative risk evaluation results,for the key cause factors control measures are put forward.Firstly,collecting the three non API performance parameters of the high grade of steel casing,vying-changning blocks of rock parameters and in-situ stress data,using statistical analysis method,the casing and rock parameters of probability distribution and probability curve equation,get three minimum yield strength of steel grade 840 MPa and 909 MPa and985 MPa.The fluctuation range of the ovality is 0.05%-0.1%,and the wall thickness unevenness is 1%-10%.At the same time,using the method of data regression fitting,the distribution curve and the distribution equation of the three-direction stress along the depth of the formation are obtained.Based on the API casing anti-collapse strength equation,the diameter-thickness ratio(diameter-thickness)-anti-collapse strength calculation model of three non-API high-grade casing in the plastic deformation stage was established under the condition of casing data optimization.Secondly,adopt the method of finite element simulation,combining with three kinds of non API high grade steel casing parameter statistics,the three kinds of the API high grade steel casing collapsing strength value is simulated,compared with the results and API standard strength model,finite element calculation results with the results of API standard deviation than the maximum is 59%,the minimum is 19%.The deviation ratio between the calculation results of the statistical model and the API standard results is 56% at most and17% at least.The deviation ratio between the calculation results of the statistical model and the finite element calculation results is 15% at most and 0 at least.The finite element calculation results are close to the calculation results of the statistical model and higher than the calculation results of the API standard values at the same time.Finally,the sensitivity analysis in finite element software modules,limit state equation of casing collapse resistance of various influence factors are analyzed.And the sensitivity of the size as a reference for establishing deformation of casing collapse accident tree,on the influence factors of casing collapse resistance detailed analysis,and combined with fuzzy evaluation and the Bayes network casing the key cause of factor analysis,for larger influence several influence factors to develop targeted preventive measures.