| During the development of shale gas wells,large-scale fracturing needs to be carried out.large volume fracturing increases the conductivity of shale formation,can effectively improve the yield of single well,but there are many casing damage in the process of fracturing,which bring difficulties to the fracturing operation and influence the production.The purpose of this paper is to study the mechanism of sliding casing failure in shale gas wells and to analyze the factors that affect the slippage.I analyzed the casing damage phenomenon in shale gas wells in Changning and Weiyuan area,the analysis shows that there are many natural fractures near the casing failure,and casing damage wells are mostly located around bedding surfaces.The correlation analysis of casing damage by SPSS software shows that there is a significant correlation between the casing damage and the fracturing fluid injected during the fracturing.Therefore,the casing damage in the shale gas horizontal well is related to the natural fracture and the slip of the bedding surface during the volume fracturing.In order to study the formation slip mechanism of shale gas well in this area,a force model of formation fracture is established,and the method of quantitative calculation of fracture surface slip is obtained by using complex variable function theory.Then,I used the COMSOL software to analyze the influence factors on the crack slip and the mutual influence between the cracks.The research shows that the slip volume of shale fracture surface reaches to centimeter level in Changning and Weiyuan area;Fluid pressure in fracture,crustal stress,rock modulus,crack length and the dip angle of the crack are the main factors that influence the slippage;The numerical simulation found that the fracture surface slip will also be affected by the change of stress of adjacent cracks.As the distance between two fractures decreases and the fluid pressure increases,the influence between them is more obvious. |
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