| The demand for oil and gas is increasing quickly with the development of world economy,conventional oil and gas resources are unable to meet the demand.By contrast,the unconventional oil and gas resources have become a hotspot for resource development because of their huge reserves and distribution.However,the disavantages such as low porosity,low permeability,and low output has limited its development.To overcome these disvantages,multistage sliding sleeve fracturing technology is an effective approach which has been widely applied in the exploitation of unconventional oil and gas resources,and has become one of the top research aspects.Previously,the study is mainly focused on fracturing process,few attention has been paid on the structural optimization and how to improve the erosion wear resistance.Severe erosion arosing from incorrect structure has limited the fracturing performance,and it is difficult to satisfy the requirement of multistage fracturing.With the funding of the National Science and Technology Major Project,this work aims to optimize the structure of fracturing sleeve,study the proppant particle induced erosion phenomenon,develop protective measures,and explore the conveyance mechanism of fracturing ball.The theoretical analysis and experimental investigation on the topic have been carried out,and the following achievements are obtained:(1)A reclosable fracturing sleeve system is developed.It is mainly composed of upper subs,lower subs,external slide sleeve,internal slide sleeve,fracturing ball,ball seat,shearing pin,sealing components,and other components.A specified switching tool for operating the fracturing sleeve system is designed.Based on the theory of two-phase flow,the fluid-solid interaction model of fracturing fluid and proppant particles is established to simulate the downhole flow status.Based on the numerical model,the inlet and outlet structure of ball seat is optimized.(2)Based on Lagrangian particulate flow model,a mathematical model of proppant particle movement in the annulus is established to study the flow and erosion characteristics in the port region.Effects of flow rate,fluid viscosity,and proppant size on pressure drop and erosion rate are studied.Based on the erosion inforamtion on the wall,a geometry evolution prediction model is proposed to investigate the geometry evolution process of eroded crater.(3)A multiple particle impact mathematical model is propsosed with the consideration of the damping and elastic-plastic behavior of target material.Three-dimensional numerical simulation for the erosion behavior on the surface of sliding sleeve has been carried out.The effects of impact velocity and impact angle on the erosion characteristics such as plastic deformation,contact time,and energy loss rate are investigated.Based on comprehensive studies,the essence of dynamic impact erosion can be obtained.(4)With regard to the erosion failure of fracturing system,the effect of High Velocity Oxygen Fuel(HVOF)treatment processes on the erosion wear resistance of fracturing sleeve is studied.The influence of impact velocity,impact angle,impact time,and particle properties on the erosion rate of samples is obtained.The erosion wear mechanism of coated specimens under proppant particles-carryring fluid two-phase flow is revealed.The protective measures to reduce the erosion rate on the surface of the fracturing equipment are given.(5)Dynamic fluid body interaction model(DFBI)is proposed to investigarte the conveyance characteristics of fracturing ball in the horizontal section.The effects of flow rate and ball size on the conveyance characteristics such as drag force,friction force,and the collision process are studied.In addition,mathematical model basig on penalty function is established to analyze the sealing process of fracturing ball.The distributions of stress,strain,and deformation under different fracturing pressures are investigated.The obtained results can provide theoretical guidance for the design and material selection of fracturing ball. |
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