A Research On Erosion Failure Mechanism Of Oil Well Sand Control Screen

For high-permeability,loosely cemented reservoirs,sand production generally occurs in the formation during actual exploitation.If effective sand control measures are not taken,oil-sand mixed fluids will cause erosion and abrasion on oil well strings and downstream equipment at the wellhead,causing Oilfield safety risks increase.Therefore,sand control has become a necessary measure for the exploitation of this type of reservoir.Oilfields generally use mechanical sieve tubes for sand control.During sand control of mechanical sieve tubes,sand particles enter the sand retaining medium to accumulate and block,causing local overcurrent "hot spots" and making mechanical sieve tubes Erosion damage occurred in a short time,and sand control of the oil well failed.Therefore,screen erosion is a dynamic plugging-erosion process.At present,scholars at home and abroad have certain limitations on this issue.In this paper,the influencing factors of sand control pipe string erosion were determined through investigation and analysis.The self-developed experimental device was used to conduct the sand control pipe string erosion test under unblocked conditions.At the same time,the commercial CFD software was used to model and simulate the multilayer screen retaining structure The simulation results were compared with experimental results to verify the erosion mechanism and erosion law of sand control pipe strings.The results show that the first layer of plain weave mesh erosion wear occurs in the front and lower weft threads near the warp yarn side,and at the same time,the surface of the warp threads between the upper weft threads also has a certain degree of erosion wear.It is mainly concentrated in the front and back areas corresponding to the meshes of the support mesh;the erosion and wear areas of the support mesh occur around the front meshes,and they are distributed at equal intervals in a stripe pattern.The erosion rate of each layer of the screen and the flow velocity increase exponentially.The erosion rate of the plain weave of the first layer is lower than the erosion rate of the plain weave of the second layer;the erosion rate of each layer is linear with the sand concentration Growth relationship;the erosion rate of plain weave mesh of each layer increases with the increase of sand particle size,and the increase decreases when the particle size is larger than 76 ?m.Based on the numerical simulation results,an empirical model of erosion under unblocked conditions was established.Based on the Fluent erosion-dynamic mesh coupling method,the evolution of screen erosion was studied,and the results showed that the pressure difference between the fluid flowing through the multi-layer screen gradually decreased with the increase ofthe erosion time,and the weft between the second layer of plain weave The flow velocity of the flow field gradually decreased;the high flow velocity region of the flow field as a whole appeared on the outlet side of the supporting mesh.As the erosion time increased,the range of the higher velocity region gradually decreased.The specific erosion rate of the first layer of plain weave mesh has little change in the initial stage,and the specific erosion rate gradually decreases and stabilizes after 15h;the specific erosion rate of the second layer of plain weave mesh decreases at first and then increases,and then decreases after 30h;Specific erosion rate increases linearly with increasing erosion time.The block and erosion experiments under different constant pressure and constant current conditions were carried out,and the block law and erosion mechanism of sand control pipe strings were further analyzed.The results show that the process of blocking sand control columns is a slow accumulation in the early stage and an exponential increase in the later stage.During this process,fine sand particles flow and erosion and wear are generated.When the clogging reaches a certain level,a periodic plugging-unblocking-plugging process occurs During the process,the sand particles extruded and the screen mesh cut and wear.Under different constant pressure conditions,the equilibrium flow rate of the sand control column is not related to the production pressure difference.The larger the balance pressure difference,the greater the screen quality loss;the larger the constant flow rate,the higher the screen pressure difference,and the greater the pressure increase.The mass loss of the screen has an exponential relationship with the change in flow.A model of sand erosion control for erosion control pipe string was established,and the model was corrected through experimental results.Finally,a dynamic erosion erosion control model for sand control string was established.