Low Permeability Reservoir Flow Characteristics Of Experimental And Theoretical Study

Generally, percolation in low permeability reservoirs does not follow Darcy's law. On the contrary, percolation characters are the existence of threshold pressure gradients, a non-linear percolation segment and a linear percolation segment which does not go though the origin.Because of characters above, it is difficult to describe the real reservoir performance applying routine percolation theories and conventional test methods in low-permeability reservoirs. Both home and abroad conduct some studies on theories and percolation mechanism experiments of low-permeability reservoirs, however, there are still many problems. Such as, there is no effective method to measure the threshold pressure gradient; studies on the judging rule for distinguishing linear flow from non-linear flow are not enough; threshold pressure gradients vary with reservoir properties, and heterogeneity of reservoir properties cause the heterogeneous distribution of threshold pressure gradients, so percolation characters in low-permeability reservoirs can not be simulated factually under the condition that threshold pressure gradient of each difference grid is equivalent.Considering problems above-mentioned, tasks conducted in this paper includes: ① designs a group of equipments to measure the threshold pressure gradient, and measures threshold pressure gradients of more than 10 rock samples;②carries out low speed non-linear percolation experiments, and plots the cure between synthetical resistance factor and Reynolds' number; ③establishes a three-dimension three-phase percolation mathematical model with considering the threshold pressure gradient, then obtains finite difference equations by numerical dispersing. In this model, the threshold pressure gradient of each grid is different from each other and is determined by the initialization parameter field. At last, simulation program is developed using the Fortran 90 language.Major studying achievements are as follows: ① on the basis of threshold pressure gradient experiment results, paper establishes the relationship cure between threshold pressure gradient and permeability; ② on the basis of low speed non-linear percolation experiments and according to existing plots between synthetical resistance factor and Reynolds' number, paper gets the "critical" Reynolds' number of a certain region, it can be used to judge whether the low speed percolation has emerged as a critical condition; ③simulation results from the new simulator agree well with which calculated by business software without considering threshold pressure gradient; ④results simulated by the new model with considering the heterogeneity of threshold pressure gradients are pretty different from which without considering the heterogeneity of threshold pressure gradients, by comparing the character of percolation field's, we find that pressure fields under two conditions differs dramatically. So, during the studying of percolation characters of low-permeability reservoirs, heterogeneity of threshold pressure gradients must be considered.Based on the experiment results, paper plots the relationship cure between threshold pressure gradient and permeability, and gets the critical Reynolds' number of a certain region; according to the heterogeneous distribution of threshold pressure...