A Study On Percolation Theory Of Fractured Low Permeability Reservoir And Its Application

It is difficult to establish an effective flooding pressure system for fractured low permeability reservoir because of developed fractures and very low permeability. Applied the fracture characterization parameters to reservoir researches, and adopted method of experiment, theoretical analysis and reservoir simulation, the laws of nonlinear percolation and development methods of these sort of reservoirs are studied.First, by a great deal of electric-analogy-modeling experiments, percolation field and productivity of well patterns under conditions of without natural fractures, as well as coupling between natural fracture and hydraulics fracture are quantificationally studied; and a new electric-analogy-modeling method is developed, by this method, percolation field and productivity of well patterns in anisotropy reservoir can be studied. These results provide foundation for optimization of well type and well pattern, which matches with natural fractures. In experiments of stress sensitivity of fractured cores, an improved method is designed to study fractured cores under force condition much closer to the reservoir condition. At the same time, the usual stress sensitivity experimental method is used, and the results of these two methods are compared and analyzed.Second, a fractured heterogeneity composite reservoir model is established, and influences of natural fracture parameters on pressure and productivity are studied. An equivalent continuous medium model of fractured low permeability reservoir is established by using tensor theory and equivalent continuous medium theory. This model combines the results of natural fracture identification and characterization with reservoir engineering research, which provides a basis to nonlinear percolation theory of fractured low permeability. Based on this model, considering start-up pressure gradient, the unsteady state flow laws of single well and inter-well interference are studied; the approaches of determining critical well spacing and critical row spacing are put forward. Considering the directions of hydraulics fracture and horizontal segment of horizontal well relatively to natural fracture orientation, the productivity equations of combined well pattern of horizontal and vertical wells, hydraulics fractured well and vertical wells, as well as well pattern of horizontal wells, are deduced respectively, and optimization methods of well pattern are given.Third, taking natural fracture parameters and start-up pressure gradient of both water phase and oil phase into account, by means of tensor theory and related percolation theory,a three dimensions and three phases percolation mathematical model of fractured low permeability reservoir is established. This model is solved by numerical method, and corresponding numerical simulation software is developed. The flow laws under complex conditions in fractured low permeability are studied by this software.Finally, considering effect of natural fractures, the well pattern type, well pattern parameters and flooding patterns are studied by numerical simulation.The research above is useful to the reasonable development of fractured low permeability reservoirs.