Pore-scale elastic microspheres were prepared controllably and their swelling property, stability, and creeprecovery property in brine water were analyzed in laboratory. The goal of the research was to study the selectivity of the porescale elastic microspheres as a novel profile control (water injection profile modification) and oil displacement agent. The matching factor between particle size of elastic microspheres and pore throat diameter of sand pack model was introduced to characterize their matching relationship. The results indicate that the optimal matching factor is 1.35−1.55. Besides, the profile control and oil displacement effect were studied using a series of heterogeneous double-tube sand pack models with optimal matching factors. The shunt flow experiments show that when the matching factor is an optimal value, the elastic microspheres prefer to plug the high-permeability layer selectivity and almost do not clog the low-permeability layer. The oil displacement experiments show that the elastic microspheres have the characteristic of plugging water without plugging oil and can improve the sweep status and oil displacement effect of low-permeability layer and low-permeability area in the high-permeability layer. According to the experimental results and actual situation of Block Liu 28-1, an optimal program for the profile control and oil displacement of elastic microspheres was proposed and conducted. The results show that the elastic microspheres can improve the water injection profile effectively. The results also confirm that the matching factor is an appropriate measure to evaluate the profile control and oil displacement effect of elastic microspheres and to guide the field test.

A novel terpolymer of acrylamide (AM), 4-vinylpyridine (VP), and 2-acrylamide-2-methylpropanesulfonic acid (AMPS) was synthesized through free radical polymerization and characterized by proton nuclear magnetic resonance, Fourier transform infrared spectroscopy, elemental analysis, and static light scattering measurement. The monomer ratio was shown to be the predominant factor to the fluid-loss control performance of this polymer in drilling fluids. The terpolymer under optimal polymerization conditions (PAAV) was prepared, and the dipolymer of AM and AMPS (PAA) was synthesized as a contrast sample. In an American Petroleum Institute (API) filtration test of bentonite-based mud with 10% CaCl 2 contamination after a 16 h aging at 150 °C, mud with 1% PAAV maintained an API filtrate volume (FL API ) of 4.8 mL, whereas mud with 1% PAA reached a FL API of 96.0 mL. The fluid-loss control mechanism of PAAV was investigated through adsorption experiments, ζ potential measurements, and particle size distribution analysis. The results illustrate that the introduction of VP units into a polymer molecule greatly improves the temperature resistance performance of the polymer and enhances the interaction between the polymer and bentonite, which improves colloidal properties of bentonite particles, and these make PAAV a pronounced fluidloss control agent in deep gypsum drilling operations.

Micron-size polyacrylamide elastic microsphere (MPEM) is a newly developed profile control and oil displacement agent for enhanced oil recovery in heterogeneous reservoirs.In this study, laboratory experiments were performed to characterize the viscoelastic properties of MPEMs in brine water. A transparent sandpack micromodel was used to observe the microscopic flow and displacement mechanisms, and parallel-sandpack models were used to investigate the profile control and oil displacement performance using MPEMs in heterogeneous reservoirs. The results indicate that MPEMs almost do not increase the viscosity of injection water and can be conveniently injected using the original water injection pipelines. The microscopic profile control and oil displacement mechanisms of MPEMs in porous media mainly behave as selective-plugging in large pores, fluid diversion after MPEMs plugging, oil drainage caused by MPEMs breakthrough, and the mechanism of oil droplets converging into oil flow. MPEMs have a high plugging strength, which can tolerate a long-term water flushing. MPEMs can selectively enter and plug the large pores and pore-throats in high permeability sandpack, but almost do not damage the low permeability sandpack. MPEMs can effectively divert the water flow from the high permeability sandpack to the low permeability sandpack and improve the sweep efficiency of low permeability sandpack and low permeability area in the high permeability sandpack. The results also confirm the dynamic process of profile control and oil displacement using MPEMs in heterogeneous reservoirs.

Knowledge of micrometer-size polyacrylamide elastic microsphere (MPEM) transport and retention mechanisms in porous media is essential for the application of MPEMs as a smart sweep improvement and profile modification agent in improving oil recovery. A transparent micromodel packed with translucent quartz sand was constructed and used to investigate the pore-scale transport, surface deposition-release, and plugging deposition-remigration mechanisms of MPEMs in porous media. The results indicate that the combination of colloidal and hydrodynamic forces controls the deposition and release of MPEMs on pore-surfaces; the reduction of fluid salinity and the increase of Darcy velocity are beneficial to the MPEM release from pore-surfaces; the hydrodynamic forces also influence the remigration of MPEMs in pore-throats. MPEMs can plug pore-throats through the mechanisms of capture-plugging, superposition-plugging, and bridge-plugging, which produces resistance to water flow; the interception with MPEM particulate filters occurring in the interior of porous media can enhance the plugging effect of MPEMs; while the interception with MPEM particulate filters occurring at the surface of low-permeability layer can prevent the low-permeability layer from being damaged by MPEMs. MPEMs can remigrate in pore-throats depending on their elasticity through four steps of capture-plugging, elastic deformation, steady migration, and deformation recovery.