Numerical Simulation Of Oil-water Two-phase Flow For Low-permeability Reservoir Of The Offshore West Korea Bay Basin In DPRK

The West Korea Bay（WKB） basin is located on Mesozoic-Cenozoic sedimentarybasin on the eastern China-Korea plate uplift background, and has experienced complexevolution process. It develops many sets of deposition, and belongs to special basin ofmulti stage, overlapping, and reformation.The WKB basin is one of a series of NE-SW rift basin formed in late Mesozoic andearly Cenozoic on thin continental crust of Korea and Eastern Chinese, its area is about2000km2.The WKB basin is one of the important petroliferous basins in Korea. Korea in thisbasin has made a lot of oil and gas exploration, and has confirmed existence of industrialoil and gas flow in the Mesozoic strata drilling WKB Basin.The WKB Basin is Mesozoic oil and gas reservoir, the reservoir experienced longtectonic action, so has many and miscellaneous pore structure type. It not only is theporosity and permeability ability is poor, but has an inclination angle, belonging to themiddle pore, fine throat of low permeability reservoir, therefore conventional Darcy’s lawis not applicable.To develop well a low permeability oil field, one should correctly understand thereservoir characteristics and seepage law, calculate the deep flow mechanics correctly, anddetermine the reasonable development program.With the development of the modern oil industry, the development of low permeability oilfield becomes more importance for the people. The low permeabilityreservoir has following apparent characteristics as compared with the middle and highpermeability reservoir: the fluid flow does not follow Darcy’s law, there is a pressuregradient flow, and the influence of gravity cannot be ignored.In this paper, for the low permeability reservoir of Mesozoic WKB Basin, throughpractical laboratory research sample, its microscopic pore structure characteristics of thereservoir are shown. On the basis of extensive research, low permeability reservoirsimulation method is studied, taking into account the pressure gradient and the influenceof gravity on the WKB Basin. The main contents and results obtained are as follows:1. Research on microscopic pore structure characteristics of Mesozoic WKB lowpermeability reservoir by applying pressure mercuryPore structure and physical properties has important theoretical and practicalsignificance in the oil and gas field development and practice. Capillary pressure dataanalysis is the most direct and effective way to evaluate reservoir pore structure. Mercurycurve in double logarithmic coordinate system is similar to hyperbolic. It is an importantmeans to study reservoir pore structure.In this paper, under the physical properties and mercury capillary pressure data oflater Cretaceous and earlier Jurassic reservoir of WKB Basin, I analysis and study of themicroscopic pore structure characteristics of the reservoir, and divide the reservoir, andprovide a reliable basis data for the further rational development of reservoir.2. Derivation and application of the formula to calculate relative permeabilitycurves considering starting pressure gradient and the gravitational influenceOil-water two-phase relative permeability curves can obviously response thetwo-phase flow characteristics. In theory, the main physical and chemical properties of thereservoir and fluid, such as permeability and pore structure, oil viscosity and oil flow ratio,and surface wettability and oil boundary layer thickness, can be reflected in relativepermeability curves. The characteristics relative permeability curves also reflect the waterflooding characteristics and effects of the different types of reservoir.Mine field relative permeability is generally obtained by indoor floodingexperimentally. In indoor relative permeability measurements, according to the theoretical basis for the experimental design, the measuring methods can be divided into two types,i.e., a "steady state methods" and "non-steady state method".Currently widely used JBN method only consider the impact of starting pressuregradient, but do not consider the influence of gravity, so there are some limitations.In this paper, using the traditional calculation of relative permeability（JBN method）,I introduced calculation method of oil and water two-phase relative permeability withconsidering starting pressure gradient under the condition of tilt formation, prepared thecorresponding utility software, and applied to oil-water two-phase relative permeability ofWKB Basin Mesozoic low porosity and low permeability oil and gas reservoirs.3. Model establishment and numerical simulation of low porosity and lowpermeability oil-water two-phase flow considering starting pressure gradient and theinfluence of gravityBased on the low permeability reservoir oil-water two-phase non-linear flow modelwith considering starting pressure gradient and the influence of gravity, I established aone-dimensional oil-water two-phase non-linear flow mathematical model for lowpermeability reservoir, constructed the corresponding finite difference format and irregulargrid system, gave a one-dimensional two-phase low-permeability reservoirs nonlinearflow numerical model. In addition, according to the mathematical model, numerical model,I solved the equation using IMPES method and constructed a corresponding computerprogram.This program was applied to one-dimensional nonlinear low permeability reservoirwater two-phase flow simulation problems under the different boundary conditions. Ianalyzed the simulation results and compared it with the actual development of dynamicto verify the correctness of the model and calculation procedures. Studies have shown thatthe impact of strata slope to low permeability reservoir develop dynamic is more apparent.