| This article is from the cooperation projects of CNPC Xibu Drilling Engineering Company Limited——Development and Related Calculation of Continuously Differential Pitching Sleeve.With the development and progress of technology in oil and gas exploration and development,the development of complex oil and gas reservoirs with low permeability and thin reservoirs has become an important development method.In particular,the development of unconventional oil and gas,such as shale gas,requires horizontal well technology with long horizontal section and the large-scale multistage fracturing technology.The use of multi-stage fracturing sleeves in the downhole and the corresponding interlayer packers increases the complexity of the downhole string,which brings difficulties to the laying of the string.Due to the complexity of the horizontal well trajectory and the multistage of the fracturing column combination,the friction becomes an important factor affecting the smooth completion of tripping the multi-packers fracturing string.If the friction is too large,the axial load of the string will increase,which may lead to bending deformation of the column or produce buckling behavior,even cause the column to self-locking and the construction of laying down the string can not be completed.In the process of setting and fracturing,due to the large internal and external pressure difference and temperature changes and other factors,making the safety of the construction of the column has become a guarantee to successfully complete the horizontal well fracturing transformation of the necessary conditions.Therefore,it is also important to study the construction safety of the setting and fracturing process.Firstly,this paper takes the multi-stage fracturing column in the horizontal well as the research object,considering the factors such as the well trajectory and the design of the column,and establishes the mechanical model of the non-packer and the multi-packers.The calculation method of the axial force and the friction resistance of the non-packer and the multi-packers string is obtained.Secondly,the buckling differential equation of the horizontal well string is deduced by the classical differential equation method,and the critical loads of the sinusoidal buckling and the helical buckling are obtained by considering the self-weight of the column,the internal pressure of the column,the external pressure of the column,the contact force between the column and the borehole.Those provide a theoretical basis for the friction of the fractured string.Thirdly,according to the actual working conditions of the setting and fracturing operations,the influence of the piston effect,the bulging effect,the temperature difference effect and the friction effect during the setting and fracturing are considered.The stress of the string during the setting and fracturing process is analyzed,and the strength of the string under complex stress is analyzed,which provides the theoretical basis for the safety of the setting and fracturing construction.The finite element analysis software of ANSYS was used to establish the model of curved pipe and horizontal pipe.According to the parameters of the actual setting and fracturing construction,the strength of the string in the construction is analyzed and compared with the theoretical calculation results,which verifies the reliability of the results.The finite element model of the packer was established by using ABAQUS nonlinear finite element analysis software,and the sealing performance of the packer was analyzed emphatically.Finally,according to the above theoretical calculation method,the C/C++language and related program development software are used to develop the mechanical calculation software of multi-stage fracturing string in horizontal wells,which provides practical tools for fracturing string design and ensuring smooth completion of fracturing.The software is now registered the software copyright by the Party A,and applied to the actual fracturing construction. |
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