Study Of Mechanism And Mathematical Simulation On The Changes In Physical Properties Of Flow System In Oil Reservoirs

The percolation in oil reservoirs is a complex system that is composed of rocks(porous media) and in-situ fluids. In the system, percolation process may make thechanges in the physical properties of the porous media and fluids. On the contrary, thephysical changes can have influence on the percolation process. In the process of oilfielddevelopment, the main occurring changes in percolation system are as follows: ①Theporosity and permeability changes: one kind of change is caused by solid particlemigration in porous media;the other is caused by other factors except particle migration;②the changes in mobility of Newtonian fluids and the rheology of non-Newtonian;③the changes in wettability of reservoir rock and relative permeability. The percolationconsidering physical property changes of rocks and fluids has been regarded as one of themost advanced research fields in modern fluid mechanics in porous medium, whichcovers many important fundamental sciences such as the rheology of non-Newtonian,transport of solid material in porous media, coupling of reservoir rocks and fluids, andnon-linear theory. The aim of this paper is to quantitatively study the physical propertychanges of oil formation percolation system and their effects on production performanceand offer technical supports for improving prediction precision of oilfield developmentand enhancing oil recovery.This study combines with oil and gas development geology, oil formation physics,oil reservoir engineering, fluid mechanics in porous media and mathematical statistics,and the effects of long-term water flooding sandstone core on macro-parameters ofporosity and permeability, micro-parameters of pores and throats and relativepermeability are studied in lab. By integrating with multi-approaches as theoretical study,oil reservoir physical simulation, constructing mathematical model, analysis foranalytical method for complicated percolation problems, the development of oil reservoirnumerical simulator and oil field example simulation, the physical property changingtendency of oil formation and fluids and their effects on percolation process are studied.Based on the previous study, the displacement theory of reservoir fluids is fartherimproved and developed, and the following models—①the percolation mathematicalmodels considering reservoir deformation and solid particles migration in porous media,②the percolation mathematical models considering the changes in wettability andrelative permeability, and ③the percolation mathematical models considering thechanges in fluid mobility and rheology, are presented. Analytical and numerical methodsare adopted to solve these mathematical models. Using Fortran 90 suiting for powerfulcomputation and VC++ with powerful ability dealing with graphics and images, anumerical reservoir simulator considering the physical property changes of oil formationpercolation system is developed. By running the simulator, the effects of oil formationcomplicated nonlinear deformation, porosity and permeability changes caused byparticles migration and sanding process, wettability and relative permeability changes, oilmobility and rheology changes on oil production performance are studied. The resultsshow that oil formation deformation, severe heterogeneity induced by fines migration andthe oil viscosity increase are adverse factors, oil viscosity decrease caused by shearingand rock wettability transfer from week hydrophilic to strong hydrophilic by waterflooding are favorable factors to exploit oil. The effects of above factors on productionperformance are too notable to neglecting. The study has important theoretical andapplication values for improving precision of remaining oil and production performanceprediction.