Study Of Numerical Simulation In Carbonate Fracture-Vuggy Reservoir With Multi-scale Features

With the continuous development of petroleum exploration on deep marine strata, an increasing number of fratured-vuggy carbonate reservoirs have been discovered, which will greatly facilitate oil and gas recovery. The theoretical model and simulation method based on traditional seepage mechanics can no longer be applied in researches on fratured-vuggy carbonate reservoirs due to the fact that such reservoirs are characterized by multi-scale feature and the coexistence of various flow states in development process. Therefore, it’s imperative to establish a series of theories and simulation methods for highly effective development of such reservoirs. Taking the space distribution of vuggy and fracture into consideration, this paper divides reservoirs into three systems on the basis of organizational structure of fractured-vuggy reservoirs:they are matrix system, macroscopic fracture system, and matrix-fracture area and large vuggy system with filler, and also merges the three systems into two mainly areas according to the flow pattern. Thus a conceptual model with flow pattern of fratured-vuggy reservoirs is proposed. Taking that conceptual model as research object, equivalent permeability tensor of blocks in different areas been calculated, for matrix-fracture area based on Darcy equation and for vuggy area based on Stokes-Brinkman equation. By using pseudo-relative permeability of up-scaled course grid, two phases differential equation of oil and water with full tensor form have been discretized and solved through 19 points difference formats. Finally, a numerical simulation method of oil and water two phase flow for fractured-vuggy reservoirs with multi-scale feature and full tensor permeability is established. In essence, the flow problem in discrete grid medium is converted into a flow problem in large scaled pseudo-continuous medium by using homogenization method and equivalence principle of flux. In this method, traditional process based on continuum mechanics can be used in analysis and solution of the flow problem in such special medium. Considering the fact that it is difficult to confirm the REV in using equivalent continuum model attribute to the existence of large scale fractures, a new method that can solve this problem and expand the application range of this model is then proposed. First we isolated the large scale fractures as a discrete medium alone and then integrated its effect into the equivalent simulation by superposition of tensor. At last, by using equivalent medium with permeability tensor instead of fractured-vuggy medium and IMPES solution, Single-phase and oil-water two-phase flow simulation models have been solved. In order to verify the validity and practicability, several cases of dynamic simulation in fractured-vuggy reservoirs are presented by using this new method. This set of methods can be applied in oil field scale flow simulation research and provide a new analysis measure for the effective development and reasonable technology policy making in fractured-vuggy reservoirs.