A Study Of An Electric-control Sliding Sleeve In The Multistage Fracturing Of Horizontal Well

Ball activated fracturing system,one of the economic wellbore treatment,enjoys a great popularity in the development of non-conventional and/or low-permeability formation,like shale gas,for it not only completes all the fracturing in one run of the string but also enhances after-treatment production rate.However,the traditional ball activated fracturing sliding sleeves embedded ball seats being of reduced size as the number of fracturing stages grow.Therefore,the hydraulic friction of the fracturing string grows gradually and obviously,and it leads to the limit of the overall fracturing number.So some further exploitation of the ball activation system is meaningful to widen its contribution to the development of non-conventional formation.In this paper,an unlimited ball activated fracturing system based on electric control fracturing plug(ECFP)is proposed.In this system,all of the downhole sliding sleeves are of the same size and active by the ECFPs,which are also of the same size,furthermore,the internal-diameter(ID)of the sliding sleeves is almost of same size as the carrier string.The implementation plan of the proposed system is carried out to overcome the primary drawback leading to the size-reducing phenomenon in the traditional ball activation fracturing system.The structure and working principle of the ECFP,magnetic-sub and sliding-sleeve-body is given in detail,and in order to provide some basic parameters for the implementation of the system,several studied are constructed described as the following text.For one thing,the motion of the ECFP in a horizontal pipe is investigated.Rather than use of the real shape ECFP,a simplified ECFP—a two flat end cylinder is adopted instead.A motion simulation based the standard k-e model,wall function,rigid body motion theory and moving reference frame theory is conducted to investigate the motion of the ECFP model after releasing from the steady state.The flow field around the ECFP model,the effect of the size and position parameters on the terminal velocity of the ECFP model is solved.The existence of the transient velocity is verified by experiment,and the linear law of the linear law of the terminal velocity fetched from the simulation has a good accordance to the experiment result.The experiment data is fitted to form a theoretical guidance for the process of the pumping of the ECFP.For another,the responding time of the ECFP is studied.The transient resonance is separated to three sub-stages.The first one is the transience of the electro-control switch,the responding time is estimated by experience.The second one is the transience of the electric-driving-system which composes of micro-DC-motor and pressure-resistant permanent magnetic actuator(PMA).The mechanical characteristics featuring the armature force and the permanent magnet(PM)torque of the PMA is deduced by an electromagnetic model and the model is solved numerically in FEA code.The simulation result is verified by experiment.The iterating equation for solving the transience of the electric-driving-system with the combination of the characteristics of the micro-DCmotor and the pressure-resistant PMA.The third one is the transience of the claw-control mechanism and it is modeled by making an analogy to the spring-oscillator system with the mechanical characteristics of the pressure-resistant PMA.The overall responding time of the ECFP could be estimated with the abovementioned study,which lays a ground work for assessing the applicability of the electric-control sliding sleeve in the development formation with multiple thin layers.What is more,the mechanics of the flexible ball seat is studied.A simple calculation model is proposed based on the energy method and a local-contact hypothesis.The relationship of the axial rigidity with the circumference deformation of the flexible ball seat when compressed is obtained.Numerical analysis is conducted to verify the calculation model preliminarily and an experiment is carried out to further verify it.The experiment result shows that the calculation model predicts 75.52% of the force needed to close the flexible ball seat.The calculation model provides a reference to the optimal design of the flexible ball seat and the design of the mechanism to activate the sliding sleeve body.Finally,a theoretical prototype is produced to test the function and performance in high temperature,high hydraulic pressure and sensing reliability.All of the performance index is subject to the expected strandline,which lays a solid foundation for a field application.