Study Of Refracturing Technology For The Shihezi Formation 8,Sulige Gas Reservoir

For the Shihezi Formation 8,Sulige tight gas reservoir with low permeability,the refracturing technology is an effective measure to improve the production.In this paper,the grey relation analysis was adopted to select the target well and layer from the refracturing candidate wells in the study area.Considering the seepage-stress coupling effect,the production-induced stress model was established with the ABAQUS software redeveloped by using FORTRAN.The stress field before refracturing was obtained based on in-situ stress field,initial artificial fracture-induced stress field and production-induced stress field.Finally,based on the stress field before refracturing,The Extended Finite Element Method was used to study the effects of permeability,elastic modulus anisotropy,and horizontal principal stress difference and production duration on the fracture deviation.Finally,field application was carried out.The work carried out in this paper and the conclusions obtained are as follows:(1)The formation data of the Shihezi Formation 8 was used to analyze the physical properties and classification characteristics of the reservoir,and obtain the distribution of Young's modulus,Poisson's ratio,compression strength and horizontal principal stress.(2)In the evaluation of candidate wells in the study area by using the grey relation analysis,the ideal candidate well was determined by the single and multi-factor method using reservoir physical parameters,initial fracturing treatment parameters and production parameters.The calculation results show that the relative Euclidean distance is inversely proportional to the similarity coefficient,the higher similarity coefficient represents the great refracturing potential.(3)Considering the mechanism of seepage-stress coupling,pore pressure/stress coupling element was established through ABAQUS/CAE platform,and the fracture flow boundary of gas well corresponding material properties and boundary conditions was defined.The dynamic evolution formulas of permeability and porosity that need to be considered in the process were written into the relevant permeability command,which were called by user-defined field subroutine when the software was running.Finally,different production flow rates were defined in different analysis steps.(4)An ABAQUS finite element model was established to obtain the initial fracture-induced stress field,and by the secondary development with ABAQUS subroutine to obtain the production-induced stress;finally,the distribution of the stress field before refracturing was obtained by using the linear superposition principle for the in-situ stress,initial fracture-induced stress and production-induced stress.(5)The distribution of formation pressure after the production process under isotropic,diagonal and non-diagonal permeability anisotropy was simulated.The results show that the variation range of formation pressure in X direction is larger than that in Y direction because the permeability in X direction is larger than that in Y direction.Non-diagonal permeability has a greater influence on formation pressure after the production process.The formation pressure after the production process distributes along the direction of non-diagonal permeability tensor.(6)The fracture deviation under anisotropic conditions was simulated.The results show that the stronger the permeability and elastic modulus anisotropy is,the larger the deviation range will be;While the smaller horizontal principal stress difference is better for the deviation range;With the increase of production time,the deviation range will increase and the trend will decrease.