| At present,the mechanism of casing deformation in shale gas Wells has been preliminary recognized and the corresponding control methods have been put forward,but the problem of casing deformation is still very serious.Therefore,it is necessary to further strengthen the research on related issues.Multi-stage fracturing operations can cause pore pressure changes around the wellbore,resulting in complex mechanical environment of casing.Therefore,the characteristics of pore pressure variation and its influence on casing deformation during multi-stage fracturing are studied in this paper.Based on the distribution characteristics of micro-seismic signals,a fluid diffusion model was established in the process of fracturing.The study shows that the pore pressure generated by fluid diffusion has an increasing relationship with the fracturing time,and a linear decreasing law with the distance to the fracture.The influence range of natural fracture on fluid diffusion and the variation value and growth rate of pore pressure in fracture are greater than those in shale matrix.Based on the clear law of fluid diffusion in the fracturing process,the variation characteristics of near-wellbore pore pressure caused by multi-stage fracturing are analyzed,and the influence of fracturing parameters is considered.The research shows that: with the increase of fracturing stages and time,near-wellbore pore pressure will accumulate in the second half of horizontal well.Natural fractures will cause non-uniform propagation of hydraulic fractures,resulting in non-uniform distribution of pore pressure near wellbore.The uneven distribution of pore pressure can be relieved to some extent by increasing the number of fracturing clusters and decreasing the viscosity of fracturing fluid.Based on the micro-seismic event points,the fracture group after multi-stage fracturing is inverted,and the influence of pore pressure changes on casing deformation is analyzed.The results show that: The accumulation and non-uniform distribution of pore pressure caused by multistage fracturing will lead to asymmetric load on casing,resulting in local stress difference,and then lead to casing deformation with different directions and displacement,showing "S" shape deformation,affecting the running of downhole tools.By adopting the “dense cutting” fracturing technology,the transformed area is more full and distributed more evenly,which effectively alleviates the non-uniformity of pore pressure distribution near wellbore and reduces the asymmetric load of casing,and effectively reduces the casing deformation rate after field application. |
