Temperature dependence of water wettability on reservoir rock surfaces: In Situ characterization and mechanistic analysis based on subcritical water properties

Abstract

The exploration of deep, high-temperature oil and gas reservoirs is increasingly critical for future energy solutions. Understanding the in-situ wettability of reservoir rocks at high temperatures is essential to prevent water phase trapping and optimize enhanced oil recovery methods. This study employs a high-temperature, high-pressure contact angle measurement system to assess water contact angles on various rock surfaces, within a temperature range of 20°C to 200°C, under an 8 MPa nitrogen atmosphere. The mechanism of temperature-dependent wettability changes was conducted using molecular simulation, atomic force microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Findings reveal that the contact angle on quartz surfaces reduces with temperature, exhibiting distinct segmented behavior. The rate of change in contact angle was approximately −0.07°/°C from 20°C to 100°C and −0.17°/°C from 100°C to 200°C. Under subcritical conditions, an increase in hydrogen bonds between water molecules and the silica surface, along with a reduction in hydrogen bonds between water molecules, markedly influences the wettability on quartz surfaces. Water contact angles on crude oil-adsorbed rock samples progressively declined with increasing temperature, from 108.3° to 52.3°, transitioning the surface from oleophilic to hydrophilic. The adhesion work of water on these oil-adsorbed rock surfaces remained nearly constant up to 100°C; beyond this, under subcritical conditions, the adhesion work surged, with a change rate of 49.14 % at 200°C. Microscopic analysis of rock surface morphology and elemental composition, combined with the physicochemical properties of subcritical water, indicated that the desorption or thermal degradation of hydrocarbons adsorbed on the rock surfaces under the action of the subcritical water significantly alters their wettability characteristics. This research offers novel insights into the mechanisms driving wettability changes on high-temperature reservoir rock surfaces and supports the development of effective strategies for preventing water phase trapping and enhancing oil recovery.