A Prediction Study Of Effective Fracture Width For Frac-pack In Unconsolidated Sand Stone Reservoir

Frac-pack technology can change the flow pattern of fluid,that is,from radial flow to bilinear flow,so as to effectively reduce the pressure gradient near the well zone and achieve the purpose of sand control and production increase.Unconsolidated sandstone reservoir has the characteristics of high permeability and strong stress sensitivity,which is easily affected by proppant embedment and fluid-structure coupling,resulting in obvious reduction of effective fracture width of frac-pack fracture in the production process,which is inconsistent with the initial fracturing design.In view of the above problems,this paper carries out the research on the prediction of effective fracture width of unconsolidated sandstone frac-pack fractures,and provides guidance for on-site frac-pack construction design.In this paper,the discrete element calculation program is written by using the numerical simulation software of particle flow.Based on the principle of three-axis servo,the discrete element model of granular accumulation in unconsolidated sandstone reservoir is established.The factors such as closure pressure,Young’s modulus and proppant particle size that affect the lithology and physical properties of proppant particle aggregate are analyzed,and the influence of each factor on the stress-strain curve and Young’s modulus of proppant aggregate is explored The fracture physical properties under the stress state of the reservoir can be characterized by the influence mechanism of the parameters such as the Young’s modulus and Poisson’s ratio.Based on the stress distribution characteristics of fractured unconsolidated sandstone reservoir,the anisotropic stress tensor is determined,and the fluid-structure coupling model of frac-pack in unconsolidated sandstone is established by using finite element method.The sensitivity analysis is carried out on the parameters affecting fracture deformation and geometric characteristics,such as initial fracture width,initial fracture permeability,stress difference coefficient and Young’s modulus of proppant The variation laws of fracture surface displacement,volume strain and equivalent permeability in the process of reservoir development are analyzed.Finally,based on the discrete element method,the proppant embedment model of unconsolidated sandstone reservoir is established,and the effects of closure pressure,proppant particle size,paved-sand content and rock hardness on proppant embedment are studied.The variation rules of proppant embedment depth and porosity in unconsolidated sandstone reservoir are obtained,and the simulation results are verified by the experimental results measured by fracture conductivity meter.This paper studies the closure mechanism of fracture width in the process of unconsolidated sandstone development,and puts forward a fracture width prediction method considering the effects of proppant embedment and reservoir fluid-structure coupling,which has a certain guiding significance for on-site frac-pack construction design.