It is indicated that the stress, deformation, permeability and porosity of rock were changed after the oil reservoir in rock mass was fractured, which led improvement of productivity. In this paper, the above problem were carefully investigated based on rock mechanic experiments and mathematical simulation. The relations between porosity, permeability and stress/strain of rocks were studied by experiment, and reservoir stress field was simulated. After the experimental data were fitted, the experimental results are justified on the basis of elasticity and capillary theories. The examples show that this model is feasible for simulating parameters of stress-strain, porosity and permeability along time and across space. And then quantitative analysis technique can be provided for reservoir development scheme, hydraulic fracturing design, and post fracturing production management. The model in this paper matches much better with the practical production than the others do.
The results of petroleum reservoir development, experimental and theoretic research showed that the interaction between multiphase fluid flow and porous rock deformation was obvious in the course of production. The fluid pressure was changed during the reservoir exploitation, and the effective stress was changed accordingly. This induced the rock skeleton deformation and resulted in the change of the porosity and permeability. Thus the fluid flow and the stress affect each other and were in dynamic balance in the process of production. So it is necessary to study the coupling multiphase fluid flow and in situ stress to get better reservoir simulation.
The porosity and permeability of ten specimens from some oilfield were measured with changing the confining pressure and the porous fluid pressures (Fig. I and Fig.2). The influence of effective stress on rock permeability is bigger than that on rock porosity. The constitutive relations between rock porosity, permeability and effective stress are studied theoretically based on elastic theory and capillary structure of porous medium. It is supposed that the porous medium and permeable space consists of bundles of parallel capillaries. The volume of capillaries is equal to the pore volume of rocks. The permeability of capillary is equivalent to that of the rock, the size of the capillaries changes with the effective stress on rock samples and the capillaries, and so does the permeability of the capillaries. Take a piece of capillary in porous medium as an example, its internal diameter-a, and external diameter-b. The ratio of single capillary volume to single element volume is defined as rock porosity. The internal pressure of capillary is p and the external pressure is Pb'. The stress distribution is apparently symmetrical. The capillary will deform elastically with the internal and external stresses according to elastic theory.
Consider a three dimensional reservoir with hydraulic fracture and fluids such as oil, gas and water.
It is necessary to solve the coupled controlling equations of reservoir fluid flow.