Enhanced oil recovery (EOR) processes have a great potential to maximize oil recovery factor of the existing reservoirs, where a significant volume of the unrecovered oil after conventional methods is targeted. Application of chemical EOR techniques includes the process of injecting different types of chemicals into a reservoir to improve the overall sweep efficiency. Surfactant flooding is one of the chemical EOR used to reduce the oil–water interfacial tension and to mobilize residual oil toward producing wells. Throughout the process of surfactant flooding, selecting a suitable surfactant for the reservoir conditions is quite challenging. Surfactants tend to be the major factor associated with the cost of an EOR process, and losing surfactants leads to substantial economic losses. This process could encounter a significant loss of surfactant due to adsorption into the porous media. Surfactant concentration, salinity, temperature, and pH were found to be as the main factors that influence the surfactant adsorption on reservoir rocks. Most of the research has been conducted in low-temperature and low-salinity conditions. Only limited studies were conducted in high-temperature and high-salinity (HT/HS) conditions due to the challenging for implementation of surfactant flooding in these conditions. This paper, therefore, focuses on the reviews of the studies conducted on surfactant adsorption for different surfactant types on different reservoir rocks under different reservoir conditions, and the influence of surfactant concentration, salinity, temperature, and pH on surfactant adsorption.

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The effect of surfactant concentration, salinity, temperature, and pH on surfactant adsorption for chemical enhanced oil recovery: a review

Electrokinetic properties of reservoir rock particles

Surfactants have been successfully used for enhanced or improved oil recovery in reservoirs having mild conditions (low temperature, low salinity). Reservoirs having harsh conditions, however, offer unique challenges in that most surfactants precipitate and chemically degrade due to a combined effect of high temperature and hardness salinity. Industry’s efforts are continuing to develop or formulate surfactants for oil recovery applications to high temperature and salinity. The aim of this study was to evaluate several modified anionic surfactants/formulations that were claimed to be able to overcome the unfavorably high-salinity brine (sea water) and high temperature and to understand the impact of high temperature to surfactant adsorption. A series of experiments were conducted to characterize and quantify the effects of aging time in high temperature (106 °C) and seawater salinity (32,000 ppm with 1600 hardness) on surfactant performance. Results for both sulfate- and sulfonate-based surfactants were deemed not to be satisfactory. Sulfate-based surfactants encountered hydrolysis problem at high temperature, whereas sulfonate-based surfactants precipitated in the presence of divalent ions. This study then focused on alkyl ether carboxylate (AEC) as the main surfactant, and blends of AEC with alkyl polyglucoside (APG). To find the optimum conditions, phase behavior tests were performed with a fixed seawater salinity but with different blending ratios of surfactant and co-surfactant, as well as overall surfactant concentrations, similar to the salinity scan. Type III microemulsion was observed for both surfactant solutions of AEC and AEC–APG blend with IFT of 10−3 mN/m (millinewton/meter). Surfactant adsorption resulted in lower adsorption in the high-temperature region. The results of this project are urgently needed by the industry for future screening in order to find suitable surfactants for applying to reservoirs with harsh conditions. The study also intends to provide an understanding of adsorption relationship to high temperature, as a guideline in addressing surfactant losses due to adsorption at high-temperature field application.

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Evaluation of new surfactants for enhanced oil recovery applications in high-temperature reservoirs

With a constant upsurge in energy demand, production from depleted and harsh reservoirs through enhanced oil recovery techniques (EOR) has significantly increased. Among many EOR techniques, chemical EOR (cEOR) is one of the most widely used methods of oil extraction. Surfactants used in cEOR are instrumental in reducing interfacial tension (IFT) and altering the wettability of rock, which leads to additional oil recovery. This review draws attention to detail on surfactants from fundamentals to field scale. Properties of surfactants like phase behaviors, critical micelle concentration (CMC), hydrophilic–lipophilic balance and deviation, zeta potential, and their importance are discussed in depth. The presence of a saline environment, polymer, cosurfactant, and other factors affecting the performance of surfactant during the cEOR process are also elaborated. Key findings on surfactant adsorption on reservoir rock with other influencing aspects have also been reported in this study. Types of surfactants, from basic to the likes of polymeric, viscoelastic, Gemini, natural, and their effects on oil recoveries have been analyzed and compared. Special emphasis on emerging aids for surfactant flooding such as applications of nanotechnology, use amphoteric Janus particles, and synergies of surfactant–low salinity water flooding, along with their mechanisms and recent advances have been thoroughly duscussed. Lastly, the review delineates discerning criteria for the selection of surfactants, reviews recent field applications, and outlines the challenges that the industry faces while implementing surfactant cEOR. It has been found that exhaustive studies have been conducted on sandstones with success. However, extreme temperature and saline conditions in the case of carbonate reservoirs limit the applicability of surfactants, and the pursuit to accomplish its efficacy continues. 

Comprehensive Review on the Role of Surfactants in the Chemical Enhanced Oil Recovery Process

Oil-in-water and water-in-oil emulsions formation and demulsification

The surfactant properties usually required for EOR are investigated with alpha-olefin sulfonates (AOS's), particularly at high temperature, salinity, and hardness, together with their solubility in brine, chemical stability, phase behavior, and adsorption. The use of a cosolvent enables aqueous solutions to be prepared with concentrated brine, even at high divalent cation levels. But the chemical stability of some solutions can be affected by their sensitivity to the oxidation of unsaturated components, resulting in a decrease of the pH. Precautionary measures to stabilize the solutions are stressed-i.e., aneorobic environment, maintenance of an alkaline pH, or addition of alcohol. As already shown, these surfactants provide low interfacial tensions (IFT's) and high solubilization parameters at high salinity and divalent cation content. Properties of optimal formulations have been investigated as a function of surfactant and cosolvent molecular weight and brine composition. Adsorption data on Na/sup -/ and Ca/sup -/ kaolinite are presented. In NaCl solutions, the amount of sulfonate adsorbed increases slightly with salinity. Preliminary measurements in hard water are shown to bring out the specific effect of calcium ions. According to the results concerning properties validly considered as screening criteria, we conclude that this family of sulfonates appears to be a potential candidatemore » for EOR.« less

Bridgitte Bazin

Papers

Surfactants for EOR: Olefin Sulfonate Behavior at High Temperature and Hardness