Productivity Prediction Model Of Network Fracturing Acidification Well Based On Discrete Fracture Network

Fractured reservoirs are abundant in oil and gas all around the world, and have very broad development prospects.Compared with the hydraulic fracturing, network fracture acidizing technology has better adaptability for this kind of reservoirs.But so far, lots of problems about productivity prediction after such stimulation still exist. First of all, there will be many complex fracture networks with high conductivity after network fracture acidizing, which has a great influence on the flow rules.Compared to the traditional multiple medium model, the discrete fracture network model can more accurately describe the seepage law of this type of reservoir. However, although the early discrete fracture network model did apply the explicit treatment to the fracture to some extent, their methods were to treat crack and matrix as equivalent medium and then superimposed them, which can present partial influence of cracks on the flow of fluids, but there are still many problems in describing complex fracture network. Second, in the process of acidification, the dissolution of matrix and padding and contaminant in fracture will greatly improve the conductivity of fracture. Now, the process to get the conductivity of etched fracture and its calculation are very complex, so the required parameters are difficult to get.According to the geological characteristics of fractured gas reservoir, this paper treats bedrock and fracture as independent systems with different flow characteristics.Based on crack submodel method, fracture submodels were established that independent of the matrix system, and coupling was accomplished by cutting the flow equations of boundaries, and then mathematical models of fractured gas reservoir with explicit discrete crack fracture were built. Next, on the basis of actual acidification data, a simplified method that calculating fracture permeability before and after acidizing was presented. Then based on the characteristics of different bedrock systems and crack models, triangle unit and mixing unit were used to discrete the models and the corresponding finite element interpolation functions were derived. And according to the seepage equations that can be obtained by virtual displacement principle, matrix and array calculated by finite element method were got, which formed finite element equation group. This equation group can be solved by the preconditioned conjugate gradient algorithm which can effectively overcome the stiffness matrix of pathological problems. Finally, based on the fracture network seepage model of fractured gas reservoir and the finite element numerical format, the corresponding calculating program was compiled. On the basis of the results verified by Eclipse, the fracture connectivity, azimuth Angle, opening and density and the effect of different acidizing measures on capacity were obtained through the sensitivity analysis of concept model.And then a set of productivity prediction basic methods and processes of a complete network fracture acidizing well were presented through a single well application examplesThis paper established a set of productivity prediction model and method of a network fracture acidizing well,which can provide theoretical foundation and method support for the productivity prediction of such wells.