Heterogeneous Flow Of Nano/Micron Polymer-particle Dispersion System In Porous Media

Dispersion system of nano/micron-sized polymer particles can enhance oil recovery of heterogeneous low-permeability reservoir effectively. Polymer particle can be adjusted by changing monomer composition and concentration of cross-linking agent in order to increase swept volume and divert displacement fluid deep in various reservoirs. However, due to surface adsorption, mechanical capture, particle bridging, inter-particle repulsion and swollen particle deformation, there occurs heterogeneous flow phenomenon such as particle aggregation, retention and selectively flowing into pore/throat etc. changing flow resistance. Therefore the key problems are to clarify the heterogeneous flow mechanism of nano/micron polymer-particle dispersion system in porous media and its effect on oil recovery enhancement.Experimental and theoretical studies were conducted on the basis of in-house AA/AM/MMA particles to investigate heterogeneous flow mechanism and its effect on EOR.1. According to particle hydration swelling experiments and rheological experiments, viscosity model of dispersion system of swollen polymer particles was proposed considering inter-particle steric force and swelling dynamic. Effect of environmental reservoir conditions, shear rate and swelling time on viscosity variation was analyzed subsequently.2. Through experimental observation of polymer particle flow in visible micro-scale porous media, two heterogeneous flow phenomena were concluded: lateral concentration profile of polymer particles in a single throat consisting of particle-free lubrication layer and concentrated core, and heterogeneous particle concentration distribution among different pore/throats. Mathematical model for lateral concentration profile was established to investigate its effect on dispersion velocity. Effect of factors such as swelling degree, shear modulus, solvent viscosity and shear rate on concentration profile and velocity profile were investigated. Subsequently, heterogeneous particle concentration distribution was mathematically modelled by introducing model for red blood cell heterogeneous distribution. Three-dimensional capillary network was established to simulate AA/AM/MMA particle flow in porous media. Particles were found to be concentrated in high-velocity paths leading to flow resistance balance.3. According to relative permeability experiment, mathematical model was established for dispersion/oil two phase flow in parallel tubes considering heterogeneous particle distribution. Simulation of relative permeability variation of dispersion and oil was conducted. Results show that compared with water-displacing-oil relative permeability, at the same water saturation oil relative permeability increases while water relative permeability decreases. It is remarkable that at high water saturation, relative permeability of water decreases obviously. The phenomenon was reproduced through simulation considering heterogeneous particle distribution, and the reason is gradual blocking of high permeable capillaries.4. Based on experimental results on block performance of polymer particles, formulas of resistance factor and residual resistance factor were obtained. Combined with heterogeneous particle distribution model, pseudo relative permeability model of flow in multi-layer heterogeneous reservoir was established. Simulation results show that with increase of polymer particle radius, concentration and injection velocity, relative permeability of water decreases.5. Two dimensional pore network model of polymer particle dispersion displacing oil flow was established. Remaining oil distribution was simulated and proportion of various kinds of remaining oil was analyzed.6. Mathematical model for profile control of multi-layer reservoir by nano/micron-sized polymer particle dispersion was developed considering local heterogeneous particle distribution. Simulation shows effect of swelling degree, injection concentration, slug size and polymer-injection time on oil recovery. It is verified that local heterogeneous particle distribution is favorable to improve sweep efficiency.The dissertation draws the following conclusions through experimental and theoretical researches. Hydration swelling of polymer particle is an important influencing factor of dispersion viscosity variation and reason for heterogeneous flow phenomena. Larger swelling degree leads to thicker lubrication layer proportion and obviously heterogeneous particle distribution. Lubrication layer causes shear thinning. Heterogeneous particle distribution causes gradual block of low-resistance pore/throats and then water relative permeability decline at high water saturation. The research clarifies effect of heterogeneous flow mechanism on remaining oil distribution and oil recovery enhancement.