Wettability of shale/oil/brine systems after exposure to silica nanofluid: a physicochemical and imaging approach

  • Ahmed Reda Metwaly

    Student thesis: Master's Thesis

    Abstract

    Precise characterization of wettability of shale/oil/brine systems is essential for understanding the fluid distribution and flow within shale microstructure. Moreover, assessment of shale wetting behavior at in-situ conditions is key for underpinning the enhanced oil recovery potential. However, shale wettability is complex and offers immense challenges due to its complex microstructure such as mineralogical heterogeneity, presence of a nano-scale layer of organic content (TOC) and varying thermal maturity. Furthermore, there is a growing interest in the use of nanoparticles to enhance oil recovery from shale oil reservoirs. Under such situations, the wettability of shale/oil/brine systems needs to be evaluated as a function of nanofluid concentration and aging time. The current understanding of shale wettability suggests that shale is mixed-wet such that the mineral matter is water-wet (hydrophilic) while the organic matter is oil-wet (hydrophobic). This wetting behavior is expected to change with a corresponding change in thermophysical conditions (e.g. pressure, temperature and salinity), while the physicochemical features such as mineralogical heterogeneity, surface chemistry, surface roughness, electrochemical interactions and the nanofluid interactions with rock surface can also influence this wetting behavior. Therefore, the objective of this study is to introduce a new physiochemical approach addressing the factors that affect the wetting characteristics of shales as well as the potential wettability alteration towards more water-wet upon interaction with nanofluids. These factors include: the surface chemistry, mechanistic features of shale surfaces, mineral heterogeneity, surface morphology, surface roughness, TOC and distribution, kerogen maturity and adsorption features at nanoscale which shall be analyzed via multiscale imaging (i.e., SEM and AFM), physicochemical set of measurements (zeta potential, FTIR, and XRD) as well as varying thermophysical conditions of high pressure and high temperature (HPHT). The wettability of three compositionally distinct US shale oil rocks (Mancos, Eagle Ford, and Wolf Camp) was assessed through advancing and receding contact angle measurements. This was followed by wettability measurements after aging the surfaces to a wide range of SiO2 concentrations (0.1, 1, 2 and 5 wt. %) and aging times. The results demonstrated a wider variability in shale surface wettability such that Mancos shale is water-wet while Eagle Ford and Wolf Camp shales are found to be strongly oil-wet. At elevated pressures, both advancing and receding contact angles increase – suggesting a more hydrophobic surface at high pressures. However, temperature effect on wettability was rather mixed i.e., both increasing and decreasing trends were noted. Importantly, upon interaction with silica nanoparticle, all shale surfaces demonstrate a shift towards a generally more water wet behavior. The chemical compositional analysis via XRD and the functional group identification via FTIR confirmed the results acquired through contact angle measurements. The outcomes of this study can shed light on the rarely covered micro/nano scale mechanistic features of shales which help in the understanding of shale wettability upon interaction with nanofluids and its possible applicability as a CEOR agent or a potential flowback additive in hydraulic fracturing.
    Date of AwardDec 2021
    Original languageAmerican English

    Keywords

    • Shales
    • Wettability
    • Nanofluids
    • Mineralogy
    • Imaging
    • FTIR
    • HPHT.

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