Investigation of wetting alteration potential of surfactants as a function of rock minerology

  • Ahmed Khalid AlZaabI

    Student thesis: Master's Thesis

    Abstract

    Surfactants are commonly used as an agent for EOR and/or as an additive in hydraulic fracturing operations. While it is known that surfactants typically alter the rock surface wettability towards more water-wet, still the mechanisms responsible for such alteration have not been fully understood and require further attention. Moreover, various surfactant wettability alteration studies lack in terms of considering the rock type and mineral compositions. Since different minerals have various surface charges, surface roughness and pore morphology, the surfactant adsorption on a mineral surface will thus be fluctuating. The objective of this study is to experimentally investigate the wettability alteration potential of surfactants as a function of rock minerology. To accomplish this, advancing and receding contact angles are measured for rock/decane/brine systems at ambient and high pressure-high temperature (HPHT) conditions before and after surfactant treatment. A broad range of rock samples are analyzed here which include: a pure calcite mineral and three carbonate samples (Indiana limestone, Silurian dolomite, Austin Chalk) while the surfactants tested include a cationic (CTAB) and anionic (SDBS) surfactants. Rock sample mineralogy is determined via X-ray diffraction (XRD) analysis while the elemental composition is acquired using energy dispersive X-ray (EDX) spectroscopy. Furthermore, Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), and Zeta potential measurements are conducted to determined surface structure/roughness, pore structure and surface charges at the rock/brine/surfactant interfaces. Additionally, Fourier-Transform Infrared Spectroscopy (FTIR) is applied to define chemical functional groups. Results indicate that increasing the concentration of surfactant does not necessarily yield better wettability alteration. Surface charges are expected to be the main driver in surfactant-mineral interface. Moreover, in this study, contact angle is generally comparable to rocks with similar mineralogy pre- and post-surfactant treatment. Factors such as surface roughness and mineral distribution influences the effectiveness of surfactant wettability modification which lead to a large range of wettability result. Rock mineralogy impacts surfactant adsorption leading to wetness change. Optimal surfactant concentrations were discovered leading to the interpretation that wettability is not directly influenced by surfactant concentration however increasing pressure and temperature leads to further wettability change towards water wetness. In summary, the use of surfactant treatment is found to be related to the rock type and minerology. Thus, this study contributes towards a better understanding of surfactant interactions with rocks.
    Date of AwardDec 2021
    Original languageAmerican English

    Keywords

    • Wettability
    • Mineralogy
    • Carbonate and Surfactant.

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