Interaction of Surfactants at Nanoscale With Water-Wet and Oil-Wet Calcite Surfaces at Reservoir Conditions

Abstract

The use of surfactants to enhance oil recovery has been introduced in the 20^th century as a tertiary stage in oil production. However, understanding interaction of surfactants with reservoir rock and recovery of the crude oil at the nanoscale has been a persistent question since then. In this study, Quartz Crystal Microbalance (QCM) and Confocal Laser Scanning Microscope are used to investigate interaction of in-house surfactant formulations with water-wet and oil-wet flat calcite surfaces at the nanoscale. Experiments are performed at close to reservoir conditions in high salinity and temperature (60k ppm total salts dissolved in water and 85 °C) using linear and branched alkyl benzene sulfonate (petroleum sulfonate) surfactants stabilized into novel formulations (NanoSurfactants). Selected temperature, salinity and calcite surface conditions are used to better represent reservoir conditions. Experiments showed that linear-surfactant-containing formulation adsorbs the most on water-wet calcite surface when compared to the branched surfactant containing formulation. Linear surfactant formulation tends to stay adsorbed in micellar form even when the solution is diluted with seawater, while branched surfactant formulation adsorbs first as micelles but break into adsorbed layered molecules upon dilution with seawater. Hence, the formulation with linear sulfonates tends to make the water-wet carbonate surface more hydrophilic than branched sulfonates. It was also calculated, by analyzing images from Confocal Microscopy taken before and after recovering oil by the surfactant solution from QCM crystal surface, that the formulation with linear surfactants recovers 53% of original crude oil from the crystal surface compared to 19% by branched. These findings at the nanoscale present a useful technique to study surfactants for Enhanced Oil Recovery applications prior to studies using more conventional, time consuming and expensive techniques such as coreflooding. In addition, this study presents us with a better understanding of a nanoscale dynamic of surfactant adsorption and crude oil recovery from the modular reservoir rock using both water-wet and oil-wet calcite surfaces.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018