Physical Simulation Test Study On Casing Deformation In Weiyuan Area

During the development of shale gas in Weiyuan block,the problem of casing deformation has always existed,which has become a difficult problem affecting the fracturing effect of shale gas wells in this block.In response to this problem,many scholars at home and abroad have done a lot of research on its formation mechanism and prevention and control measures,but the problem of casing deformation has not been well solved.The reason for casing deformation in Weiyuan block is mainly due to the uneven shear stress field generated by shale formation under hydraulic fracturing,which causes the shale formation to slip along the natural weak surface,and the casing will shear after the formation slips.And the amount of slip shear is mostly centimeter.In this paper,the corresponding physical simulation experiment is carried out for the large-scale shale gas well casing change problem in the Weiyuan block.It is hoped that through the means of indoor simulation experiments,the laws of the set-up of the Weiyuan block will be revealed,and the theoretical control methods and suggestions for the set-up will be provided for the site.Firstly,the paper analyzes the engineering geological factors of shale gas well casing deformation in Weiyuan block,and studies the location characteristics of the casing deformation,the morphological characteristics of the casing deformation,the fracture characteristics of the stratum near the set point and the set.The comprehensive analysis considers the casing deformation mechanism of shale gas wells in Weiyuan district: First,due to the expansion and shale of the shale layer under the action of fracturing,the formation slips and shears the casing;Second,because the fracturing fluid is immersed in the bedding plane,the friction coefficient between the bedding planes is reduced and the normal stress is reduced,which in turn aggravates the occurrence of slippage caused by slippage of the shale layer.Secondly,the rock mechanics parameters of the Longmaxi Formation shale were tested.The compressive strength,elastic modulus and Poisson's ratio of the cores at different angles from the bedding direction under uniaxial and triaxial experimental conditions were determined.It provides basic data for subsequent shale gas well stratigraphic slip-induced physics simulation experiments.Finally,based on the theory of abnormal state similarity,the indoor simulated stratum parameters of the inter-rock strata physics simulation experiment are determined,and an indoor physical simulation experiment device is designed.The device was used to carry out the physics simulation experiment of stratigraphic slip caused by stratigraphic gas wells in Weiyuan block.The results show that the slippage of the stratum is mainly related to the distance from the deformation center of the stratum,that is,the distance from the hydraulic fracturing point,and the slip amount reaches the maximum at 70-80 m from the hydraulic fracturing point;Different stratum thicknesses and different stratum depths affect the amount of stratum slip.When the casing passes through a shale stratum with a thick layer thickness,the slip amount is larger than that of the lowthickness stratum;When the casing undergoes multiple stages of deformation through the formation in the longitudinal direction,the upper shear slip is greater than the lower portion.At the same time,the numerical simulation is carried out based on the physical simulation experimental parameters.The results show that the physical simulation results have a high coincidence rate with the numerical simulation results,and the average coincidence rate is 93.76%.