Study On Near-well Detailed Numerical Simulation Method Of Shale Gas Reservoir

In recent years,with the growing demand of oil and gas energy globally and the development of horizontal well hydraulic fracturing technology,shale gas reservoirs have gradually become a hot spot at home and abroad.After hydraulic fracturing,complex fracture network structures can be formed in near-wellbore reservoirs around horizontal wells in shale gas reservoirs,which results in gridding problems in near-wellbore areas when using conventional methods to do numerical simulation so that the computing workload is large and hard to converge.Therefore,it is necessary to find a more stable and efficient numerical simulation method for the detailed simulation of the shale reservoirs especially around the horizontal well areas.In this paper,a detailed near-wellbore shale reservoir numerical simulation software was compiled using a novel EDFM numerical simulation method.Finite volume method and full implicit solution is applied in this method.Physical processes such as the adsorption and desorption,Knudsen diffusion,slippage effect and stress sensitivity is fully considered in our flow model.An improved meshing method,fine meshing method,is conducted in this EDFM simulation.Matrix and fractures are meshed individually and then coupled according to their positional relationship in this method,which is simplified and adaptable.In the wellbore model,equivalent wellbore permeability concept is introduced so that it can be coupled with the gas reservoir model.This method is verified by comparing its numerical simulation results with the simulation results in COMSOL,a commercial numerical simulation software.At last,through the calculation of several sets of examples,the influence factors of shale gas reservoir productivity were analyzed,and the optimization design of fracturing parameters was carried out.Research results show that the novel EDFM simulation method presented in this paper is an improvement over the existing numerical simulation methods.It can simulate the complex DFN in near-wellbore reservoirs accurately as well as maintain a high calculation efficiency and strong applicability.The analysis results of the influencing factors of shale gas reservoir productivity show that the early production rate and cumulative production of shale gas increase with the increase of the fracture half length,the number of farctures,and the distribution density of natural fractures;Knudsen diffusion has a strong effect on the cumulative production when the matrix permeability is very small;the impact of stress sensitivity is mainly in the early and mid-term,and the predicted cumulative production will be larger without considering the stress sensitivity;the impact on production capacity is mainly reflected in the middle and late period,and the longer the time,the greater the impact.The fracturing parameter optimization design results are as follows.To reach the highest economy benefit,fracture conductivity should be design by 10 or so.The best well spacing should be 220 meters when the 10-year production is the main indicator.Reservoir linear flow is much more efficient than external reservoir linear flow,so that the key to optimizing well spacing is to maximize the internal linear flow.