Understanding of the Fluid Flow Mechanism in Porous Media of EOR by ASP Flooding from Physical Modeling

Abstract

Abstract The fluid flow mechanism in porous media of enhanced oil recovery by Alkli/ Surfactant/ Polymer (ASP) flooding is investigated by measuring production performance, pressure distribution and saturation distribution through installing differential pressure transducers and saturation measuring probes in a physical model of vertical heterogeneous reservoir. The fluid flow variation in reservoir is the main reason of enhanced oil recovery of ASP flooding, while the pressure field and saturation field are nonlinearly coupled together and the interaction between them results in the fluid flow variation in the reservoir. In a vertical heterogeneous reservoir, the ASP agents initially flow in high permeability layer, and fluid changes the flow direction toward low and middle permeability layers because the resistance in high permeability layer is increased under the physical and chemical action of adsorption, retention and emulsion etc. ASP flooding not only displaces out the residual oil in high permeability layer, but also displaces out the remaining oil in low and middle permeability layers by both increasing swept volume and displacing efficiency. Introduction Nowadays, most oil fields in China are in the production later period, and the water cut increases rapidly with even over 80 percent. It is hard for water flooding technique to meet the needs of oil fields production. Thus it is inevitable to develop new oil production techniques to replace water flooding. ASP flooding is a new technique which is developed out on the basis of alkali flooding, surfactant flooding and polymer flooding in the late 1980s. ASP flooding synthetically make use of the benefits of the above three flooding methods, and oil recovery is enhanced greatly by decreasing interfacial tension, increasing capillary number, enhancing microscopic displacing efficiency, improving mobility ration and increasing macroscopic sweeping efficiency.[1] In recent years, many intensive and deep researches have been done on ASP flooding both in China and in the world, some important achievements and recognition have been obtained, which lays the solid base for the practical application in oil fields[2–4]. The ASP flooding mechanism was studied visually by using microscopic scale model and double plane glass model with sand in reference[5–6]. In these experiments, the water viscosity finger, the residue oil distribution after water flooding and the oil bank formed by microscopic emulsion flooding were observed. In reference [7–8], it was observed that the main mechanism of ASP flooding are deformation, threading, emulsion(O/W) and strapping are the main mechanisms of ASP flooding in water-wetting reservoir, and that the main mechanism of ASP flooding are interface producing, bridging between inner-pore and outer-pore, emulsion(O/W) in oil-wetting reservoir. In a vertical heterogeneous reservoir, ASP flooding increases displacing efficiency by displacing residual oil through decreasing interfacial tension, simultaneously improves sweeping efficiency by extending the swept area both in vertical and plane direction. Some physical and chemical phenomena such as emulsion, scale deposition, chromatographic separation are occurred in the process of ASP flooding[9–10]. Many very complicated physical chemistry fluid flow in porous media are involved in ASP flooding, there still remain a lot of oil recovery mechanisms needing to be solved. By far, most researches have been done on microscopic displacement mechanism of ASP flooding, while the fluid flow mechanism in porous media in macroscopic scale lacks sufficient studies. In this research, a vertical heterogeneous reservoir model is established, and differential pressure transducers and saturation measuring probes are installed on the model. The fluid flow mechanism of increasing both macroscopic sweeping efficiency and microscopic displacing efficiency is studied by measuring production performance and the variation of pressure distribution and saturation distribution in ASP flooding. An experimental data base of ASP flooding is set up, and the data provide the experimental base for numerical simulation