Wettability Alteration in Tight Sandstones During Long-Term Shut-In Following Hydraulic Fracturing

After the hydraulic fracturing operation, the fractured wells can be shut-in for extended periods of time to allow hydrocarbons to accumulate in the fracture before starting production. In this work we study the meso-scale wettability alteration in tight sandstone reservoirs during the long-term exposure to the broken hydraulic fracturing fluid (bHFF) during the well shut-in period; 24 cylindrical samples (2.54 cm dia x 0.5 cm thick) of tight Scioto sandstone are prepared using a precision core cutting machine. The samples are divided into two groups: half of the samples (“wet samples”) are vacuum saturated with a light sweet crude oil, and aged for 3 weeks at 200 psi and 90 °C to ensure uniformly oil-wet rock while the other half (“dry samples”) are cleaned with air plasma to remove contaminants and establish hydrophilicity. The contact angle is then measured using both: captive bubble and sessile drop method, and the samples are aged in bHFF. Two samples are removed after 3, 7, 15, 30, and 60 days and the contact angle are measured again. X-ray diffraction on the rock samples show that it consists primarily of quartz with small presence of albite. The contact angle for the dry and wet samples are measured as 26.76° and 81.78° respectively. Preliminary results show that the wettability of the tight sandstone changes with exposure to the bHFF. Contact angle measurements indicate a shift from water-wet to intermediate-wet, with the effects more pronounced in the wet samples. There is a dearth of data with regards to long-term interactions between the broken hydraulic fracturing fluid and tight sandstone formations and this study aims to fulfil this gap by following at the evolution of the surface petrophysical properties of the rock. This work reveals significant long-term risks with post-fracture shut-in and offers valuable data to improve the hydraulic fracturing design and reservoir management strategies in unconventional plays.