Abstract

Practically all enhanced oil recovery (EOR) processes require mobility control techniques to minimize channeling, gravity override, and viscous fingering of the displacing phase. In oil reservoirs that contain free gas, high gas-oil ratio production is a widespread problem, because gas segregates as a result of its higher mobility. This condition may cause reduced oil production rates, loss of drive energy, loss of recoverable oil, and problems with fluid processing. Use of foam as mobility-control fluid has shown promise in a wide range of EOR techniques including steam flooding, CO2, light hydrocarbon or N2 injection, and chemical flooding. The success of any mobility control process, including foams, is determined by the microscopic displacement efficiency of the displacing fluid at pore level. Microscopic displacement efficiency is determined by the interactions of rock pore geometry and interface boundary conditions, which constitute the reservoir wettability. To date limited information has been published regarding the role of wettability in the performance of foams as mobility control agent, accordingly more evaluation is needed.

The focus of this experimental research was to determine the effect of wettability on the performance of foamed gels in displacing oil and in its efficiency as a mobility control and blocking agent. The experimental observations were made through a series of displacement tests using unconsolidated porous media with an average permeability of 511 mD. The wettability of the porous media was modified using an organic coating solution. The oil phase used was soltrol and the foamed gel formulation was based on a partly hydrolyzed polyacrylamide crosslinked with chromium (III) acetate, and an anionic surfactant.

The experimental outcome indicated that mobility control performance of foamed gels is sensitive to the wettability of the porous media. Furthermore, the injection of foamed gels in high permeability porous media demonstrated an efficient fluid diverting capability, which renders important additional oil recovery.

Introduction

Extensive theoretical, laboratory, and field studies have been performed to evaluate the use of foams as mobility-control agents during steam and high-pressure gas floods (1). The majority of these investigations have been carried out in oilfree water-wet media, while few of them have been carried out in the presence of oil or in intermediate to oil-wet media (2). Petroleum reservoirs can exhibit a wide range of wettability from water-wet to oil wet. Therefore, it is of considerable interest to understand how rock wettability influences foam stability and performance (3).

Currently, the limited information that has been published on cores made artificially oil-wet can be classified in two groups base on their conflicting experimental results and way of thinking. The first group of researchers (4–7) supports the general notion that foam formation as well as propagation through porous media is favored by water-wet surfaces or the rigid opinion that foams are stable only in a strongly water-wet medium. This school of thought states that foam will become unstable in oil-wet media because of lamellae detaching and collapse. The work of Sanchez et al. (4) demonstrated that foam formation in an oil-wet porous medium in the absence of oil is possible because of the alteration of the surface from hydrophobic to hydrophilic.

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