Determining Pore Level Mechanisms of Alkaline Surfactant Polymer Flooding using a Micromodel

Abstract

Abstract Primary recovery methods such as water flooding recover as much as 50% of the original oil in place and therefore end up leaving remaining oil that is less likely to be produced behind in the reservoir. In fractured reservoirs, the recovery efficiency is even lower as water prefers to channel leaving a considerable amount of uswept reservoir. New techniques have been introduced in order to access this unrecoverable potential; these techniques are assembled in what is called Enhanced Oil Recovery (EOR). Enhanced oil recovery processes play a major role in increasing the recovery efficiency and extracting the inaccessible oil that has been trapped in a reservoir. One type of enhanced oil recovery applicable to waterflood reservoirs is alkali surfactant polymer (ASP) flooding. Polymer flooding (PF) and alkaline/surfactant/polymer (ASP) flooding have been known and in practice for more than 20 years. These processes have shown successful results during large-scale implementations in China, for instance. ASP flooding is a form of chemical enhanced oil recovery (EOR) that allows operators to extend reservoir pool life and extract incremental reserves currently inaccessible by conventional EOR techniques such as water flooding. The combination of all three chemicals is synergetic. The surfactant is ultimately used to lower the interfacial tension between the oil and the injected water. The alkali reacts with the acidic portion of oil to produce in-situ soap (surfactant) and the polymer increases the injection water viscosity to reduce the possibility of channeling and viscous fingering during the process. The objective of this study is to grasp a better understanding of the mechanisms of ASP flooding will by conducting several experiments in carbonate micromodels. A micromdel is a two dimensional porous medium created by etching a pore network into silicon. Pore-level mechanisms are observed directly using a micromodel. The challenge is to understand how the combination of alkali, surfactant, and polymer allows us to best access the matrix and efficiently sweep the oil. Therefore, a screeting study was conducted to evaluate diverse surfactants of concentrations ranging from 0.5 to 5.0 % by measuring the interfacial tensions in order to select one compatible with light crude oil (27°API). Both secondary and tertiary flooding of the ASP slug was tested at realistic flood rates of 0.1 m/day Darcy velocity. Greater flow rates were later attempted to maximize recovery, within the reasonable pressure range that the micromdel can handle, to maximize recovery. The results are presented in the form of image analysis of microscopic pictures taken at different locations to estimate the oil recovery. The ASP displacement experiments conducted yields reasonable improvement of recovery for all cases.