Staged Fracturing String Mechanics Analysis In Oil And Gas Development

Staged fracturing is a key technology for unconventional oil and gas development,which includes dual packer staged fracturing,perforation bridge plug combined staged fracturing,multistage sliding sleeve cementing staged fracturing,multi packer sliding sleeve staged fracturing and coiled tubing hydraulic jet staged fracturing.As the channel for transporting fracturing fluid,the segmented fracturing string and cementing casing string will withstand drastic changes in thermal stress and internal and external pressure,which is prone to deformation and failure;At the same time,the setting failure of packer and the excessive friction of long horizontal drilling bridge plug string seriously affect the success or failure of segmented fracturing operation.Therefore,it is of great significance to the safe operation of fracturing operation through predicting the mechanical state of segmented fracturing string.However,there are still some limitations in the research of mechanical analysis of pipe string in staged fracturing operation.Therefore,this paper systematically carries out the mechanical analysis of fracturing operation string under different working conditions,and compiles the calculation program with MATLAB.The research results are of great significance to optimize the design of segmented fracturing operation string and ensure the safety of fracturing operation.This paper firstly analyzes the string structure and operating conditions of different staged fracturing technologies,and puts forward the hydraulic jet staged fracturing technology with automatic nozzle replacement.The segmented fracturing string can be divided into segmented fracturing string(SFS),cementing casing string(CCS)and drilling bridge plug string(DBPS).The wellbore temperature field distribution of hydraulic fracturing well and liquid nitrogen fracturing well is solved.A two-dimensional unsteady heat transfer hydraulic fracturing well wellbore temperature field mathematical model considering annulus injection conditions is established.The ADI alternating direction implicit method is used to discretize the model.The calculated results verify the accuracy of the model;The coupling model of transient temperature field in the wellbore of liquid nitrogen fractured wells considering liquid nitrogen phase change is established for the first time and the effects of fracturing parameters and insulating tubing performance are analyzed.The mechanical analysis mathematical models of segmented fracturing string in the whole fracturing cycle based on three-dimensional wellbore trajectory are established.Taking the SFS in different segmented fracturing technologies as research object,the mechanical analysis mathematical models of SFS in the whole fracturing cycle based on three-dimensional wellbore trajectory are established.The calculation results show that increasing the friction coefficient will reduce the axial force of the fracturing string and lead to the growth of the spiral buckling section.Then,the experimental method is used to verify the influence of the cuttings bed in open hole wells on the friction coefficient.Taking the CCS as research object,the mechanical analysis model of staged fracturing CCS before and during fracturing is established,and the influence of fracturing parameters on the stress of CCS is analyzed.Considering the effects of various factors such as wellbore structure,wellbore trajectory,internal and external pressure and temperature,the casing-cement sheath-formation stress model of segmented fracturing well is established.The results show that the variation of wellbore temperature with well depth should be considered,the bending stress has a significant impact on the strength of the casing,the non-uniform induced stress field caused by fracture leads to the reduction of casing strength,and the casing safety factor of liquid nitrogen fracturing well is small under the condition of conventional cementing.Taking the DBPS as research object,the mechanical analysis model of DBPS is established,and the influence of radial vibration on friction torque of DBPS is studied.Aiming at the problem of supporting pressure of pipe string with bridge plug in horizontal well,the torque of horizontal rotating drill string installed with different drill pipe joints under different drilling speed and rotating speed is tested using self-developed test-bed,and a new method of reducing friction and torque of drill string by using radial vibration is proposed.