Capillary Pressure Behavior of CO2 - Shale System at Elevated Temperatures

In this study, changes in capillary entry pressure of shale when interacting with CO2, under different temperatures have been investigated. The combined impact of temperature and petrophysical properties of shale (water content, water activity, permeability and porosity) on capillary entry pressure was addressed.  Pressure breakthrough measurements were used to evaluate the minimum entry pressure of CO2 through shale.  A heavy-duty oven was used to vary the temperature in order to investigate the impact of temperature on CO2 capillary entry pressure through shale.  Results showed that capillary entry pressure of shale when interacting with CO2 was highly affected by temperature. Higher temperatures decreased capillary entry pressure of shale. We believe that pore dilation, where pore throat size expands due to the application of heat, may have caused this decrease in capillary entry pressure.  However, in some cases higher temperature activated clay swelling that may have caused an apparent decrease in pore throat radii of shale which translated into higher capillary entry pressure.  Results also showed that there exists no distinct relationship between petrophysical properties of shale and its measured capillary entry pressure when interacting with CO2 at different temperatures.  Heat could alter pore throat radii and cause pore dilation which may alter measured capillary entry pressure.  Interfacial tension decreases with increasing temperature and that can be attributed to the weakening of intermolecular forces at the two immiscible fluids interface. Swelling of clay could be related to temperature-induced transition from passive to an active clay.