Study On Numerical Simulation Of Thick And Low Permeability Gas Reservoir

Poor reservoir properties make it very complicated to develop thick,low permeability gas reservoirs,and the time and cost of acquiring capacity analysis data through testing have also increased considerably.Reservoir productivity prediction is often an important part of a gas reservoir developing program.At the same time,due to the existence of vertical fluid seepage in the thick and low-permeability gas reservoirs,and the high-speed erosion of the reservoir water by the formation gas,the irreducible water is transported into the movable water,which aggravates the heterogeneity of the reservoir.Makes the contradiction between development of gas reservoirs more prominent.Therefore,in view of the special seepage mechanism of lowpermeability gas reservoirs,it is necessary to establish a method to evaluate the productivity of low-permeability gas reservoirs,and to provide theoretical guidance for the effective development of thick gas reservoirs with low permeability.Based on the investigation of the research on the thick and low permeability gas reservoirs at home and abroad,according to the reservoir characteristics of thick and low permeability gas reservoirs,the main controlling factors influencing the productivity of the thick and low permeability gas reservoirs are optimized.A mathematical model for the seepage flow of thick and low-permeability gas reservoirs considering the stress-sensitive,movable water-initiated pressure gradient and gas-water phase infiltration time-variation is established.The finitevolume method is used to discretize the established mathematical model and its discrete format is performed.Detailed derivation,linearization of the nonlinear terms appearing in the derivation process.There are two ways to mesh the formation: the PEBI mesh and the corner mesh.While using PEBI unstructured grid to finely disperse gas reservoirs,according to the seepage characteristics of gas reservoirs,the gas reservoirs are divided into six major regions such as boundaries,faults,vertical wells,horizontal wells,fractures and backgrounds.According to the fluid percolation characteristics in each region,different methods are used to generate reservoir subdivision point sets.Based on the points set,a Voronoi diagram of these grid points is generated using the Fortran algorithm.Based on this Voronoi diagram,a PEBI grid can be generated for the area of the gas reservoir.While using a corner grid to discrete the gas reservoir area,according to the characteristics of the corner grid system,the shape of the contact surface between two adjacent corner grids and its judgment method are discussed in detail.At the same time,the area of the contact surface is calculated,and then the conductivity between the two adjacent corner grids is solved.A simulation program is developed based on the above research results.The program is mainly divided into two parts: the first part can realize the mesh division of the formation,including the corner grid and the PEBI grid;the second part completes the numerical simulation of the gas reservoir,which solve the problems that the current commercial software can not handle the time-varying gas-water relative permeability.Use the established conceptual model to complete the software reliability verification.The effect of special seepage mechanism of thick and low permeability gas reservoir on its productivity was studied by self-developed program,which provides a theoretical basis for the development of thick and low permeability gas reservoirs.