Wettability Alteration of Kerogen by Interacting with Hydraulic Fracturing Fluid

Abstract

The recent increase in unconventional oil and gas exploration and production has promoted active research on hydraulic fracturing, but the impact of interactions between fracturing fluid and kerogen on the alteration of kerogen wettability has not been well understood. The objective of this study is to experimentally estimate the changing wettability of kerogen with various thermal maturity levels by the interactions with hydraulic fracturing fluid. To achieve the objective, kerogen was isolated from a bulk rock of organic-rich shale with different types and maturities. Kerogen isolates was kept in a mix with synthetic hydraulic fracturing fluid under the temperature of 80 °C for 14 days. Relative changes of sulfate ions were analyzed by using Ion Chromatography (IC). In the measurement of kerogen wettability, sessile drop method was applied to measure the direct contact angle by utilizing the Drop Shape Analyzer (DSA). During the reaction with hydraulic fracturing fluid, kerogen isolates were analyzed by conducting functional group analysis, which provided the supplemental information on the wettability of kerogen. Functional groups of kerogen were analyzed by using the Attenuated Total Reflectance Fourier-Transform Infrared spectroscopy (ATR-FTIR). The reaction of fracturing fluid and kerogen isolates from various organic-rich shales were conducted, and it is experimentally demonstrated that the interactions between kerogen and fracturing fluid would cause substantial wettability alterations in organic pores and fractures that depend on the types and maturities of kerogen. The DSA results indicated that the air/water-contact angle decreases after the reaction, regardless of the types and maturities of kerogen, while the higher level of maturity of kerogen led to a greater change of air/water-contact angle. The results of ATR-FTIR showed that the hydrophobic functional groups were lost in the mature kerogen isolates, and they were potentially lost in the relatively lower level of maturity-kerogen isolates due to the oxidation, indicating that the kerogen showed increasing hydrophilicity, which provided a strong support to the DSA results. This study experimentally determined the wettability alteration of kerogen by interacting with organic additives in hydraulic fracturing fluid. The results of this investigation will provide a significant step forward in evaluating the multiphase fluid transport in organic-rich shales with the wettability alteration and resulting hydrocarbon production.