Research On Damage Mechanism Of Volume Fracturing Casing In Horizontal Well

In the development of shale oil and gas resources,horizontal well volume fracturing technology can further increase reservoir permeability by "breaking" the reservoir,thus effectively achieving reservoir stimulation.However,with the widespread use of related technologies,casing deformation failure caused by fracturing appears,which seriously affects the effect of resource development.Therefore,this paper uses the finite element method to analyze the influence of volume fracturing on casing deformation,in order to clarify the casing failure mechanism caused by volume fracturing in horizontal wells,and provide reference for fracturing on site and casing design methods.The research methods and results adopted in this paper are as follows:(1)By establishing a global embedded fluid-solid coupling fracture propagation model to simulate the volumetric fracturing process of shale reservoir,the changes of crustal stress distribution,formation displacement and fracture propagation after volumetric fracturing are determined when cluster spacing,horizontal crustal stress difference,formation elastic modulus,injection flow rate and slip fracture dip angle change,the distribution of stress and displacement in near-wellbore formation under corresponding conditions is analyzed in the meantime.The results show that in the process of volume fracturing,under the influence of complex and irregular fracture propagation degree,the near-wellbore formation is stressed unevenly,which increases the possibility of casing deformation failure;When natural fractures open and slip occurs in the process of fracturing,the larger the Angle between the sliding surface and the wellbore,the shorter the opening length of the fracture and the smaller the slip distance.(2)Establishing casing deformation model without formation slip to determine the casing force and the casing diameter change when cluster spacing,horizontal crustal stress difference,formation elastic modulus,injection flow rate change.The results show that the decrease of cluster spacing,horizontal crustal stress difference,formation elastic modulus and injection flow rate will increase the casing deformation degree,and the casing failure will be caused when the deformation is serious.(3)Based on the formation slip condition under different inclinations of natural fracture,a casing-cement ring-formation integrated model is established to further analyze the influence of different formation dip angles on casing shear deformation.The results show that the formation slip distance increases with the decrease of fracture dip angle,and the casing shear deformation becomes more significant;the probability of casing shear failure caused by formation slip is great.Therefore,measures should be taken to avoid casing shear failure due to related problems.(4)On the basis of using API criterion to determine the maximum allowable casing internal pressure,combined with relevant data,the casing deformation model without formation slip is used to determine the influence of cluster spacing,horizontal crustal stress difference,formation elastic modulus and other parameters on the casing internal pressure strength in volume fracturing process.The results show that the maximum equivalent stress on casing increases with the increase of internal pressure when the casing body is subjected to uneven load.In addition,when the cluster spacing and formation elastic modulus are too small,the internal pressure value of casing pipe body does not reach the theoretical maximum,yielding phenomenon occurs;Based on the numerical simulation results,the API casing compressive strength formula is modified to make it suitable for the strength design of volumetric fracturing casing.