This paper presents a method to analyse the mixed oil, gas, water flows and transmits in a crack-damaged rock mass. The fluxion process is modelled as a seepage problem of multiphase fluid, which flows in a crack-damaged porous medium with a double porosity. Based on the principle of conservation and transmission for mass, kinetic momentum and energy, a mathematical model of non-linear dynamics for the multiphase fluid and seepage in the crack-damaged porous medium has been suggested. In the model, a saturation factor of phase state and a damage state factor have been taken into account as the basic variables of the system. The damage growth and porosity evolution have been considered as a dynamic process due to coupling between the seepage field and the deformation field in the rock mass. The developed model has been applied into the numerical analysis, in order to simulate the forecast of the storage and the optimisation for extracting the oil and natural gas.
Subterranean porous medium (such as crack-damaged rock mass) has been the source of valuable fluids such as ground waters and petroleum, both liquid (oil) and natural gas. Actually,most of petroleum and natural gas are extracted from the subterranean porous in cracked rock mass. The mixed flow of water, oil and gas in subterranean porous medium can be considered as multiphase fluid. Since it involves multifarious coupled phenomena in subterranean seams such as the transformation of mass, the release of energy, the flow of combined gas and liquid and the deformation of rock strata. Therefore, the problem has a strong non-linearity, and the solution of this problem is very complex and hard to be found in the general ranges. The mechanism of migration of multiphase fluid (such as water, oil and gas) in the crack-damaged porous medium is an invisible and complex physical system both for reservoir engineering and mining engineering. Thus, the successful research of this problem may not only present a more satisfactory method to forecast the reserves of oil and gas but also possible to provide more efficient equipments for economic production (Slider 1976). Subterranean porous formation has been used for the injection of polluted liquids and for cover up the hazardous chemicals or radioactive products in the ground. Certain special geologic structures have also been used for the seasonal storage and quick recovery of already processed petroleum products and natural gases. The propose of this paper is to develop a numerical approach, which will provide a computational method for predicting the flow characteristic of multiphase fluid migration in the crack-damaged rock mass due to hydraulically fractures. The major objective outlined in this study is to take into account the combination of the Thermodynamics (heat and mass transfer), Multiphase Fluid Dynamics (oil, gas and moisture flow), Solid Mechanics (medium deformation) and Continuum Damage Mechanics (damage evolution of porous) as well as the Hydraulically Fracture Mechanics in the resource engineering problems. It was then proposed to develop a two dimensional finite element formulation.
