Article pubs.acs.org/Langmuir
Static Adsorption of an Ethoxylated Nonionic Surfactant on Carbonate Minerals Guoqing Jian,† Maura C. Puerto,† Anna Wehowsky,† Pengfei Dong,† Keith P. Johnston,‡ George J. Hirasaki,*,† and Sibani Lisa Biswal*,† †
Department of Chemical and Biomolecular Engineering, Rice University, Houston, Texas 77005, United States McKetta Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712, United States
‡
S Supporting Information *
ABSTRACT: The static adsorption of C12−14E22, which is a highly ethoxylated nonionic surfactant, was studied on different minerals using high-performance liquid chromatography (HPLC) combined with an evaporative light scattering detector (ELSD). Of particular interest is the surfactant adsorption in the presence of CO2 because it can be used for foam flooding in enhanced oil recovery applications. The effects of the mineral type, impurities, salinity, and temperature were investigated. The adsorption of C12−14E22 on pure calcite was as low as 0.01 mg/m2 but higher on dolomite depending on the silica and clay content in the mineral. The adsorption remained unchanged when the experiments were performed using a brine solution or 0.101 MPa (1 atm) CO2, which indicates that electrostatic force is not the governing factor that drives the adsorption. The adsorption of C12−14E22 on silica may be due to hydrogen bonding between the oxygen in the ethoxy groups of the surfactant and the hydroxyl groups on the mineral surface. Additionally, thermal decomposition of the surfactant was severe at 80 °C but can be inhibited by operating in a reducing environment. Under reducing conditions, adsorption of C12−14E22 increased at higher temperatures.
1. INTRODUCTION In recent years, CO2 foam1−5 has attracted attention for use in enhanced oil recovery because it is effective at increasing the displacement efficiency by offering mobility control6−8 in heterogeneous reservoirs. Surfactants9−11 are typically used to stabilize the foam. The choice of surfactant12−14 for the CO2 foam enhanced oil recovery (EOR) process is highly dependent on the reservoir and fluid properties, such as rock lithology, reservoir temperature, salinity, and oil. The general criteria for the use of a surfactant in a CO2 foam process are its effectiveness in generating foam in porous media,15−17 low partitioning into the oil phase,10 low adsorption onto the rock surfaces, and high thermal stability under reservoir conditions.11 Adsorption18−20 is one of the most important aspects when selecting a surfactant for EOR. The retardation of the surfactant front caused by adsorption onto the formation rock may make the oil recovery process inefficient and economically challenging. Therefore, the adsorption behavior of a surfactant needs to be systematically investigated prior to its application in chemical EOR.21,22 A variety of surface forces plays a major role in surfactant adsorption onto the rock surface. These interactions can be attractive or repulsive depending on (i) surfactant charge, (ii) charges and wettability of the rock/brine interface, (iii) brine ionic strength, composition, and pH, and (iv) temperature.23−28 Typically, anionic surfactants show high adsorption © XXXX American Chemical Society
on calcite and low adsorption on silica, while cationic surfactants show the opposite results due to electrostatic interactions between the surfactant and minerals. Additionally, compared to an air environment, CO2 was found to decrease adsorption of cationic surfactant cetylpyridinium chloride (CPC) on dolomite and limestone surfaces by increasing the ζ potential of the mineral surfaces.23,24 Zwitterionic surfactants are sensitive to brine ionic strength. Nieto-Alvarez et al.25 showed that the adsorption of a zwitterionic surfactant, cocamidoproyl hydroxysultaine (CAHS) on limestone, was much higher under high salinity compared to low salinity. They also found that temperature did alter the zwitterionic surfactant adsorption onto mineral surfaces. Rock wettability in the presence of residue oil also influences surfactant adsorption by preferentially partitioning to the brine/oil interface, resulting in phase trapping.26−28 Nonionic surfactants are promising candidates for CO2 foam EOR in carbonate reservoirs29−32 because electrostatic interactions between the surfactant and the rock surfaces are negligible. However, the low cloud point33,34 of conventional nonionic surfactants limit their application at elevated temperatures and in high-salinity reservoirs. Recently, Chen at al.10 Received: May 26, 2016 Revised: September 9, 2016
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DOI: 10.1021/acs.langmuir.6b01975 Langmuir XXXX, XXX, XXX−XXX
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and sodium sulfite (Na2SO3, certified ACS reagent, >98%, SigmaAldrich) were utilized as received. The representative carbonate mineral used is Silurian dolomite powder, which was prepared by crushing with a ceramic mortar and pestle (Silurian dolomite outcrop, Kocurek Industries). Then, the resulting powder was sieved through a 140 mesh (≤105 μm) steel wire screen followed by washing. The dolomite was dried at 115−125 °C in a vacuum oven (15−20 in. of mercury) for 10 h. All of the surfactant solutions were prepared with deionized water (18.2 MΩ·cm). The other studied minerals include ScienceLab dolomite (≤74 μm, ScienceLab Inc., Catalog No. SLD4477), calcite (≤5 μm, Alfa Aesar, Catalog No. 11403), silica (
