The Digitally Simulated Study On The Micro-Displacement Efficiency Of Viscoelastic Fluid

This dissertation is an integral part of "The Study on the Improvement of polymer flooding" which is a subcategory of the national project No.863--The Study on the Advancement of Recovery Ratio of Polymer Flooding in Bo Hai Oil Field and "The Design and Synthesis of the Highly Effective New-Type Polymer Molecular" which is the subcategory of the national project No.973—The Fundamental Study on the Advancement of Recovery Ratio of Chemical Flood and Microbial Enhanced Oil Recovery.The technology of polymer flooding, which can improve the recovery ratio of the water flooded crude oil by 10%, plays a critically important role in tertiary oil recovery. Traditional theories hold that polymer flooding can only increase the sweeping efficiency, not the oil displacement efficiency. As the virtual viscosity ascertains the level of sweep efficiency in polymer flooding, it seems that there is little room for the further development of this technology. Great controversies prevail in the academic world regarding whether and polymer viscoelasticity helps to improve efficiency of the micro-displacement and in what ways and how largely can it be improved, which are inadequately certified by the claim obtained through laboratory experiments that strong evidence of "pull" and "drag" effects are shown when the polymer solution viscoelasticity is in displacement. Therefore, whether polymer flooding can be further developed lies in the key of how polymer solution viscoelasticity can enhance the efficiency of the micro-displacement.Resorting to the method of digital smulation, this article systematically studies and proves academician Luo Pingya's Deformation Piston Hypothesis:"plunger flow" can be formed if rheological behavior of the fluid amounts to certain value when the Viscoelastic structure fluid is leaking through porous-medium capillary. If the cohesive force of Viscoelastic fluid is greater than or equals to the cohesive force of oil and the wettability of earth layer is water wet, the irreducible oil in the capillary can be completely displaced; if the wettability of earth layer is oil wet, all the irreducible oil can be displaced except the layer of oil film on the pipe wall. Under the constant change of interstice and bottle neck, the viscoelasticity of polymer solution swells and the binding pressure and inertia effect can be enlarged and expanded to the edge of interstice to occupy its space, so that a "deformation piston," changing along with the shape of interstice, can be formed to continue its "plunger flow" in the interstice. The confirmation of Deformation Piston Hypothesis can build a solid theoretical foundation for possibility of using polymer fluid to improve displacement efficiency.So far the research on the mechanism of viscoelastic fluid's micro-displacement is still in exploration and in lack of full certification. Those researches are dominated by the micro-displacement facilitated in-door experiment and theoretical analysis. The method of Computational Fluid Dynamics used in this article, in union with those traditional ones forms a complete study system of micro-displacement's working mechanism.This article first examines the oil displacement mechanism of polymer and the development of oil displacement applicable polymer and finds that the rheology of polymer solution in oil displacement can directly influence its flowing dynamics and oil displacement efficiency in the leaking core passage. Then a detailed introduction is given to the theoretical foundation and developmental trend of CFD simulation technology as well as the possibility and study methods of applying CFD simulation technology to the analysis of polymer solution's micro displacement mechanism. DFD's protruding strength lies in the fact that in essence it is applicable to the study of fluid's movement under any circumstance. The adoption of simplified mathematical models in CFD aims at improving calculation efficiency and meeting the present equipment of computer hardware. If the condition of computer hardware allows, mathematical model which is most suitable to the study of flowing substance can be used to solve any problems concerning flowage.With the assistance of rheology performance testing platform of fluid sweep efficiency and a sample of an underground location fifty meters distant to the mouth of a well in Bo Hai oil field, this article measures the rheological parameter of three types of fluids and establishes a linkage between these three types of fluids with reference to the elastic parameter of fluid in certain shear rate.The most actual PPT constitutional equation for differential viscoelastic model is adopted, based on Polyflow, flow characteristic curve of viscoelastic fluid is calculated and analyzed, elasticity of viscoelastic fluid has important affection on fluid microscope swept area, under the same condition, the fluid has higher elasticity need lower pressure. With the increasing of elasticity of fluid, the turbulence in shrink hole comes into being, whose intensity is in direct proportion to elasticity. The turbulence proves that the fluid has better displacement characteristics. At last, the capillary filling efficiency of three fluids are quantitative analyzed. In this paper, the relationship between fluid macroscopic rheological parameter and its conduct in microscope displacement is established.According to alter the proportion between elastic variable and pore model of polymer solution, it was found that under the known reservoir, through the adjustment of effective viscosity, laxity time of elastic coefficient, displacement fluid forms deformation piston under microscope displacement condition, conformance efficiency is amplified; According to control the deformation recovery capability of polymer solution and expandability through throat (viscoelasticity), displacement efficiency of polymer flooding is enhanced.These studies above provided the necessary theoretical and experimental basis for reference about the scope of mechanism, methods and approaches using polymer rheology (including shear flow and tensile flow rheology) to increase the oil displacement efficiency by a large margin, simultaneously,the evaluation of polymer selection; provided reference for increasing the polymer flooding efficiency greatly, and promoting the development of tertiary oil recovery.