Research On Nonlinear Percolation Law Of Heavy Oil

As conventional oil reserves gradually decline, heavy oil resources more and more get the people attention, and with the development of the thermal extraction technology, the exploitation of heavy oil is gradually expand the scale, output continues to grow, thermal recovery of heavy oil in the oil industry has been occupies the important position, therefore, more and more people research on it,, part of heavy oil has been listed as key development projects, heavy oil exploitation will increasingly shows the important strategic position. Therefore, understanding of formation fluid in the reservoir seepage law is the foundation of the development of reservoir. But due to its own characteristics of heavy oil, the show is different from conventional crude oil in underground seepage characteristic of its choice of reservoir development, technology and development indicators and so on have influence, so the correct understanding of heavy oil seepage characteristics, provides the basis of scientific theory for the effective development of heavy oil reservoir and technical support.Heavy oil is also known as the crude oil and bitumen in the international, it is a complex, multicomponent homogeneous organic compounds, it mainly composed of alkanes, aromatics, colloid, asphaltene. With the increase of colloid and asphaltene content, the relative density and viscosity of heavy oil is increased. Therefore, high viscosity and high density are the main characteristics of heavy oil, this is also the major indexes of the difference between the conventional crude oil. The viscous properties of heavy oil, associated with its chemical composition,crude oil is a complex mixture consisting of a series of various types of large molecules, and not at a molecular level dispersion of uniform true solution system, but there is some form of super molecular structure, the molecular structure belong to dispersed phase, inhomogeneous colloidal dispersions. Is due to the structure characteristics of heavy oil, resulting in heavy oil has the characteristics of non-newtonian fluid, and the seepage characteristics in porous media is different from conventional crude oil, general performance for nonlinear seepage. One of nonlinear seepage features is possible exist start-up pressure gradient. Only when the displacement pressure gradient exceeds the start-up pressure gradient,heavy oil began to flow, and the seepage law deviating from the darcy’s law.This article first to study QHD32-6oil field and SZ36-1oil field crude oil rheology studies, through the experiment to verify the non-newtonian of crude oil of the target blocks. Secondly, based on the analysis of nonlinear seepage flow at home and abroad in recent years the determination of start-up pressure gradient method and the cannot be neglected. In addition, by studying the target block of heavy oil seepage law, found that start-up pressure gradient have been supported by the mobility, start-up pressure gradient decreases with increasing mobility. In addition, when the flow is small, with the increase of the mobility,the flow of start-up pressure gradient descent quickly; When beyond a certain range, with the increasing mobility of the start-up pressure gradient decline slowed. The greater viscosity of crude oil, the bigger the start-up pressure gradient. Under the condition of irreducible water of start-up pressure gradient degree less than pure start-up pressure gradient of oil phase. By QHD32-6oil field and SZ36-1oil field crude oil of single phase and two phase seepage curve measurement result shows that with the same viscosity, under the conditions of different permeability core gas logging permeability is lower, the curve of the axis offset to the pressure gradient. Suggests that the lower the permeability, the smaller the pore of rocks, the lower the flow rate under the same pressure difference, the finer the participation of pore fluid flow pressure gradient, the greater the need.