An Extensive Study of the Thermal Stability of Anionic Chemical EOR Surfactants - Part 1 Stability in Aqueous Solutions

Abstract

If chemical stability of EOR polymers has been extensively studied over the past decades, surfactants have attracted less attention except for a few reference papers. This article presents existing and new data on the chemical stability of a variety of surfactants classically used for EOR applications in aqueous solutions. The aim is to clarify under which reservoir/operational conditions each surfactant types and combinations can be safely used regarding chemical stability. Anionic surfactants, including alkyl benzene sulfonates, internal olefin sulfonates, alkyl ether sulfates and alkyl glyceryl ether sulfonates are investigated. Their thermal stability is monitored in a wide range of conditions: temperature from 25 to 120°C, pH, oxygen level… Their performance in terms of solubility and interfacial tension reduction is monitored through classical bulk aqueous tests over several months. In addition, liquid chromatography and two phase titration are used to identify any loss of integrity of the studied products. Results indicate that both hydrolysis and oxidation mechanisms should be considered to guarantee long term stability of EOR surfactants. Hydrolysis sensitive surfactants, e.g. alkyl ether sulfates, undergo hydrolysis with associated loss of performances at high temperatures. This is shown to be true even in alkaline conditions as pH essentially impacts degradation kinetics and not inner stability. This study also shows that properly selected EOR surfactants and blends can withstand very harsh conditions (up to 120°C) for several months allowing high confidence in EOR process performance along with time in a reservoir. Oxygen management is however critical to achieve such performance. This paper initiates a series of articles giving a clear framework for safe use of surfactants in oil reservoirs regarding their chemical integrity. It is intended to provide reliable guidelines for products selection, lab evaluation and field application. These aspects, often underestimated or simply by-passed in some EOR studies, are critical to ensure field trial success in challenging conditions.

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

“…Surfactants are widely used and have a very large number of applications, especially in the petroleum industry for enhanced oil recovery (EOR) process because of their ability to influence the properties of the rock surface and oil-water interface (Puerto et al 2012;Lu et al 2014;Hesham et al 2018). Surfactant is a surface acting agent, and they can adsorb at a surface of the fluid-fluid interface to alter the surface properties significantly, thus reducing the surface tension and interfacial tension (Hocine et al 2016). The interfacial or surface tension is a measure of the difference in nature where the two phases are meeting at the interface or surface; the higher the dissimilarity in their natures, the higher the interfacial tension or surface tension between them (Rosen 2004;Hadian et al 2018;Hematpur et al 2017).…”

Nonionic and anionic surfactants as flowback aids in hydraulic fracturing methods of crude oil production

“…These and other surface measurements must also be performed under formation conditions along with an assessment of surfactant thermal stability. The nonionic and anionic surfactants employed herein are stable to 90°C in both their neat forms and in aqueous solution (Indorama Ventures Public Co., Ltd., internal data), however, the presence of substances in the formation rock and the oil as well as salinity, pH and oxygen levels, may each affect stability, which is most critical in EOR applications for which surfactants are expected to perform over long periods (Hocine et al, 2016).…”

Long-Term Thermal Stability of Ionic Surfactants for Improving Oil Production at High-Salinity High-Temperature Conditions

“…In addition, Angstadt et al also highlighted the excellent stability of linear alkyl benzenesulfonate for temperatures up to 300 °C during steam injection in low-salinity conditions . Under high-salinity conditions, Hocine et al reported the degradation of sulfates and sulfonates up to 120 °C in months. , Regarding the thermal stability of types of surfactants, the concluding results showed that alkyl benzenesulfonate was superior to olefin sulfonate and petroleum sulfonate, which were more robust to temperature than sulfate surfactants. The degradation mechanism includes the loss of sulfonate or sulfate function by hydrolysis in an acidic or alkaline media, , along with oxidative attacks on the side alkyl chain when exposed to oxygen .…”