Oil Recovery Mechanisms of Alkali-Surfactant-Polymer Flooding

Abstract

The experimental study includes phase behavior tests, measurements of interfacial tension (IFT), and coreflood tests. Effects of alkali (sodium carbonate) additives on micro-emulsion phase behavior were determined for a reservoir oil. No emulsion phase was generated for low surfactant concentrations without alkali additives, while an emulsion phase was always formed with alkali. Measurements of the dynamic IFT revealed that when the alkali concentration is as high as 0.7–1.0 wt%, the IFT rapidly increases after about 100 minutes, which suggests that the system shifts from the middle to upper-phase equilibrium. Based on tertiary alkali-surfactant-polymer (ASP) coreflood tests with surfactant and polymer concentrations of 1.0 wt% and 1200 ppm respectively, an optimum alkali concentration was confirmed as 0.2 wt% that allowed the highest recovery. Using the optimum ASP concentrations, another series of corefloods were conducted to evaluate the effect of remaining oil saturation at the start of ASP flood. Mobile oil helps alkali and surfactant slugs form an oil bank. In order to examine the oil recovery by high alkali and low surfactant concentrations (1.3 and 0.1 wt%, respectively), corefloods were conducted by changing the injection volume and scheme. Only a small incremental recovery is obtained with ASP slugs higher than 0.2 PV each. The injection scheme of polymer slugs is confirmed to be crucial for ASP flooding. Parallel coreflood tests as physical simulation of ASP flood in a two-layer system showed recovery performances complicated not only by permeability contrast but also by small-scale heterogeneity within inidividual cores. Acceptable matches between coreflood experiments and one-dimensional flow simulation were obtained by modeling ASP flood with recovery mechanisms of the surfactant-polymer flooding.

Investigation of the microscopic displacement mechanisms and macroscopic behavior of alkaline flooding at different wettability conditions in shaly glass micromodels

“…Arihara et al (1999) concluded the oil recovery mechanisms by alkali-surfactant-polymer flooding in sandstone reservoir. They proposed that at alkaline concentration below 1 wt% the wettability reversal mechanism predominates so that the rock wettability is changed from strongly oilwet to the lesser oil-wet condition.…”

Alkaline/Surfactant/Polymer (ASP) Flooding

“…By altering the wet ability to the water-wet condition and reducing the interfacial tension to ultra-low values [4], it is possible to enhance oil recovery and provide a solution to oil retention problem. An injected fluid is required to be injected into the matrix of a fractured formation for EOR rather than into the fractures.…”

“…To meet the requirements of crude oil supply, more and more efforts have been placed on not onlyexploringnew oil reservoirs, but also further improving of oil recovery from the mature reservoirs [2,3]. The improvement of oil production from mature oil fields is an important strategy from both economic and technical points of view [1,2,4]. According to the oil recovery history [5,6], there are three stages of oil extraction, which are primary, secondary, and tertiary technologies [7].…”

Detection and Reuse of the Produced Chemicals in Alkaline-Surfactant-Polymer Floods

“…Field applications of alkaline floods alone usually result in poor oil recovery due to the alkaline loss caused by the chemical reactions with the reservoir rocks, low acid number of the crude oil, and adverse mobility ratio 10 . The major EOR mechanisms of an ASP flood are briefly described as follows.…”