Research On Law Of Impact Bare Well-wall Cracking And Safety Assessment In Shale Gas Well

With the rapid development of the national economy and the acceleration of industrialization,the demand for energy is getting larger and larger in our country,and the contradiction between supply and demand has become increasingly prominent.As a clean,efficient and new type of energy,shale gas has gradually gained worldwide attention Currently,multilateral well are generally used for the production of shale gas.However,during the drilling of multilateral well,due to the complicated well shape and the change of geological structure,the wellbore stability problem at the juncture of branch wells has become a problem that have to be taken into account in the exploitation of shale gas and largely determines the economic benefits and drilling safety of shale gas development,during the drilling process,the high velocity impact of cuttings particles on the shaft wall rock is also one of the important factors that cause the wall instabilityBased on the literature data and the data provided by the oil field,the finite element numerical simulation technique and the Drucker-Prager criterion are used as the criteria for rock fragmentation.An explicit finite element model of the junction of branch wells is established to study the stress distribution of rock strata and the branch well junction rock crushing characteristics under the effect of ground stress.Aiming at the shaft wall broken caused by high speed impact of debris particles during the drilling process,an explicit dynamic impact model of wellbore-cuttings particles is established by explicit finite element theory,study the force state and the broken state of the shale wall under cuttings erosion,and change the particle impact parameters to study the rock wall broken law under different parameters.Finally,based on the theory of safety assessment,multi-factor comprehensive safety analysis of wellbore stability is carried out.By identifying the risk factors in the stability of wellbore,the safety evaluation index system is established,qualitative and quantitative analysis of risk factors by AHP,based on the results of numerical simulation,fuzzy mathematics is used to evaluate the safety of borehole wallThe crushing characteristics and stress distribution of the rock at the junction of branch wells under the action of in-situ stress are obtained.Through the calculation of the explicit dynamic impact model,the stress fluctuation status and the crushing characteristics of the rock under the impact of the rock debris particles are obtained.By changing the particle impact parameters,the rock stress changes and the crushing rules are obtained.The multi-factor comprehensive safety analysis of the stability of the borehole wall,the system safety evaluation results are obtained.In this paper,by numerical simulation of the finite element model of juncture of multilateral well and safety evaluation of wellbore stability,we hope to provide some reference for reducing the collapse of wellbore during the actual operation.