Static Adsorption of Surfactants on Bakken Rock Surfaces in High Temperature, High Salinity Conditions

Surfactant EOR received attraction due to its extreme capability to increase displacement efficiency by altering the wettability, lowering the oil/water interfacial tension and ultimately mobilizing the residual oil. However, surfactant systems are widely acknowledged to have large adsorption on rock/clay/sediment solid surfaces, which may result in concentration loss, thus impair the effectiveness of the chemical solution and turn the process into an economically unfeasible case. Surfactant adsorption can be affected by the adsorbents, surfactant structure, experimental temperature and some other factors. Also, the driving force for adsorption varies with different surfactants types. Generally speaking, electrostatic interaction is more prominent for those anionic surfactants, while hydrophobic interaction is more common for nonionic type. In this paper, the static adsorption behaviors of two surfactants (A1 and N1) on Bakken minerals and Berea sandstone in high salinity and high temperature Bakken conditions (salinity≈290,000 mg/L, temperature=80~105 °C) were studied using spectrometric iodine method, where 0.1 mM I2-0.2 mM KI solution was used as a color developing agent. The primary stability indicated that both surfactants have high compatibility with the Bakken formation brine at high temperature, and their critical micelle concentrations showed a small decrease in the presence of high saline brine. Bakken mineral is relatively complicate, which is composed of quartz, dolomite, calcite and clay, while Berea sandstone contains over 75 wt% quartz. Herein, the effects of surfactant concentration, surfactant type, temperature, adsorbents and salinity on adsorption density were covered, and the impacts of surfactant concentration and adsorbents were found to be more significant. Due to the higher specific surface area and high clay content of Bakken minerals, both anionic surfactant blend A1 and nonionic surfactant blend N1 have pretty high adsorption on Bakken minerals, and the specific adsorption densities of 1000 mg/L surfactant solution were calculated to be 1.74 mg/m2 and 1.69 mg/m2, respectively. Meanwhile, the results also indicated that though the applied surfactant concentration is relatively low, the concentration loss due to adsorption should never be overlooked. Future study on how to effectively reduce the adsorption of surfactant especially in those clay-rich formations is of great significance.