| The technology of plug-and-perforate combined staged fracturing is the main method used in unconventional oil and gas development at home and abroad.However,in the later stage of the construction,it is necessary to use the coiled tubing to connect the milling tool to drill bridge plug for the smooth flow of oil and gas.The complicated drilling process of the bridge plug and the problems brought about by it restrict the application of the technology of plug-and-perforate combined staged fracturing in the unconventional oil and gas reservoir reconstruction.The development of the free drilling large diameter bridge instead of the traditional composite bridge plug has been developed,so as to avoid the drilling process of the bridge plug in the later stage of construction.According to the demand of enterprises and site to design a large diameter bridge plug and the three key problems of the sealing performance,the the anchoring effect of anchoring mechanism,the tool itself on the oil and gas throttling action determine the functional requirements are studied in detail.Summarize the research content of this paper,including the following aspects:(1)The functional requirements of the large diameter bridge plug are analyzed,the principle scheme is determined,and the overall structure design is completed.The detailed structural design of the main parts of large diameter bridge plug is carried out.The paper gives some suggestions on the selection of the tool for the closure of large diameter bridge plug.(2)The finite element model is established to simulate the expansion of the expansion ring along the expansion cone and the simulation analysis of the contact pressure between the rubber cylinder and the casing.The variation of the stress of the rubber cylinder,the contact pressure of the cylinder and the casing with the load and the hardness of the cylinder were analyzed and the effect of seating load and hardness on the plugging performance of large diameter bridge plug was studied.The plugging performance of large diameter bridge plug is evaluated.The possible maximum value of the seating load and the hardness of the rubber cylinder is discussed.(3)The finite element model of the simulation analysis of the interlocking of slip and casing is established,and the stress cloud diagram of the slips and the casing and the contact pressure nephogram are obtained.The effect of slip anchor is analyzed and evaluated.A selection of tooth tip radius,slip angle,slip angle of tooth parameters that have a greater impact on anchoring effect for the three factors,respectively,analyzing their impact on anchoring effect of the slip.The optimized structure parameters of slips are determined when anchoring effect is best.(4)Using CFD software Fluent to simulate the internal flow field of the large diameter bridge plug,and to study the throttling effect of the large diameter bridge plug.Combined with the main contents of this paper,the research results are as follows:(1)The principle scheme of the large diameter bridge plug is determined,the overall structure design is completed and the structural design of the main parts is carried out by using mechanical knowledge and finite element simulation analysis.Compared with common bridge plug setting tool,combined with the structural design,gives reasonable suggestions on the selection of the tool for the closure of large diameter bridge plug.(2)The stress of the rubber cylinder,the contact pressure of the rubber cylinder and the casing are increased with increase of setting load and hardness of the cylinder.The maximum stress of the rubber cylinder is located at the right shoulder,which appears flow to the annulus.The maximum contact pressure between the rubber cylinder and the casing is located at the contact area between the right shoulder of rubber cylinder and casing,which is about 65 MPa,which can meet the design requirements that sealspressure difference of 60 MPa.The right shoulder of the rubber cylinder plays an important role in cutting off wellbore pressure difference.The greater the contact pressure between the right shoulder of the rubber cylinder and the casing,the better the plugging performance of the large diameter bridge plug.The maximum setting load of the large diameter bridge plug should not exceed 182 KN and maximum hardness(HA)of the rubber cylinder should not exceed 88.(3)Slip teeth and casing inner wall occlusion is not uniform.In the axial direction,upper teeth and casing wall occlusion effect is stronger than lower teeth and casing wall occlusion;In the longitudinal direction,slip teeth and casing wall occlusion effect is descending from the middle to the end.The micro plastic deformation of upper tip of slips has little impact on tip embedding casing wall and root of slips will not break down.The casing does not appear permanent damage.The 7 teeth of slips were occluded with inner wall of the casing,and the tips of the 5 teeth were embedded into the inner wall of the casing.Slip anchor effect is better.(4)The slip stress,casing stress,contact pressure of slips and casing are decreased with increase of the slip fillet radius.Based on the analysis of the influence of slip fillet radius on the anchor effect,the optimum range of the fillet radius is 0.3 ~ 0.4mm.The slip stress,casing stress,contact pressure of slips and casing are increased with increase of the slip cone angle.Based on the analysis of the influence of slip cone angle on the anchor effect,the optimum range of the cone angle is 17 o ~ 20 o.The slip stress,casing stress,contact pressure of slips and casing are decreased with increase of the slip apex angle.Based on the analysis of the influence of slip apex angle on the anchor effect,the optimum range of the slip apex angle is 90 o ~ 95 o.(5)Using CFD software Fluent to simulate the internal flow field of large diameter bridge plug and results show that whole flow field pressure distribution is stable,less fluctuant,pressure difference changed little and flow resistance is relatively small.The overall velocity distribution and change of flow field is consistent with the actual situation.The throttle pressure difference of large diameter bridge plug is small,which is about 0.03 MPa,the throttle effect is not obvious and meet functional requirements. |
