Study On Multi-field Coupling Model And Its Application For Heavy Oil Reservoir Porous Media

With the hot fluid injection and recovery of oil and gas, stress field and temperature field in reservoir porous medium will be redistributed in the process of thermal recovery of heavy oil. It led to the physical parameters change of reservoir. Changes of porosity and permeability have influence on the seepage of oil and gas in rock pores. Therefore, heavy oil thermal recovery is a typical multi-field coupling process. The composition and structure of reservoir porous media pores are diverse, some of the characteristics parameters are difficult to obtain. So it is difficult to do precise description and analysis. And the current multi-field coupling models are for specific conditions have some limitations.Supported by National Natural Science Foundation of China (51176023), this paper presented the REV (representative elementary volume) description method of reservoir porous media, and analyzed the mechanism of multi-field coupling theory of reservoir porous media. Combined with REV, the author established "three box" model, including black-box model, gray-box models and white-box model, and proposed "black boxâ†'gray boxâ†'white box" analysis process of porous media. Based on the models heat and mass transfer process of reservoir porous media REV was analyzed; black-box and gray-box models thermal conductivity calculation formulas of REV was derived, and heat balance equation of heat and mass transfer process was given. Combined with the basic differential equation of seepage and auxiliary equation, multi-field coupling mathematical model were given. Taking our reservoir thermal recovery situation into account, this paper analyzed the thermal conductivity variation effected by the variation of porosity and pore distribution, and some results were make:1.With the increase of the porosity, the thermal conductivity becomes smaller;2.When the thermal conductivity value of the rock is close to oil, total thermal conductivity changes linearly; series, parallel and total thermal conductivity values are in the same size; when the thermal conductivity difference between oil and rock is large, the total thermal conductivity appears curved distribution;3.When the coefficient of pore channel distribution is much larger, the total thermal conductivity curve is more approaching to the series curve.Using CMG-STARS to simulate heavy oil thermal recovery processes, heat and mass transfer characteristics of steam flooding were analyzed, and obtained some useful results. This paper provided a new idea and method to analyze the porous media multi-field coupling.