Oil Recovery Mechanisms of Alkali-Surfactant-Polymer Flooding

摘要

The experimental study includes phase behavior tests,rnmeasurements of interfacial tension (IFT), and coreflood tests.rnEffects of alkali (sodium carbonate) additives on microemulsionrnphase behavior were determined for a reservoir oil.rnNo emulsion phase was generated for low surfactantrnconcentrations without alkali additives, while an emulsionrnphase was always formed with alkali. Measurements of therndynamic IFT revealed that when the alkali concentration is asrnhigh as 0.7–1.0 wt%, the IFT rapidly increases after about 100rnminutes, which suggests that the system shifts from the middlernto upper-phase equilibrium.rnBased on tertiary alkali-surfactant-polymer (ASP)rncoreflood tests with surfactant and polymer concentrations ofrn1.0 wt% and 1200 ppm respectively, an optimum alkalirnconcentration was confirmed as 0.2 wt% that allowed thernhighest recovery. Using the optimum ASP concentrations,rnanother series of corefloods were conducted to evaluate therneffect of remaining oil saturation at the start of ASP flood.rnMobile oil helps alkali and surfactant slugs form an oil bank.rnIn order to examine the oil recovery by high alkali and lowrnsurfactant concentrations (1.3 and 0.1 wt%, respectively),rncorefloods were conducted by changing the injection volumernand scheme. Only a small incremental recovery is obtainedrnwith ASP slugs higher than 0.2 PV each. The injection schemernof polymer slugs is confirmed to be crucial for ASP flooding.rnParallel coreflood tests as physical simulation of ASP flood inrna two-layer system showed recovery performancesrncomplicated not only by permeability contrast but also byrnsmall-scale heterogeneity within inidividual cores.rnAcceptable matches between coreflood experiments andrnone-dimensional flow simulation were obtained by modelingrnASP flood with recovery mechanisms of the surfactantpolymerrnflooding.