Pore-scale contact angle measurements at reservoir conditions using X-ray microtomography

- A new method for the extraction of contact angle from micro-CT images is presented.
- This method is applied to the CO2-brine-water system at 10 MPa and 50 °C.
- A distribution of contact angles is seen, ranging from 35° to 55° with a mean of 45°.
- The range arises from surface roughness variation and contact angle relaxation.
- Measurement error is analysed and found to be small for this system.

Contact angle is a principal control of the flow of multiple fluid phases through porous media; however its measurement on other than flat surfaces remains a challenge. A new method is presented for the measurement of the contact angle between immiscible fluids at the pore scale at reservoir conditions (10 MPa and 50 °C) inside a quarry limestone through the use of X-ray microtomography. It is applied to a super-critical CO2-brine-carbonate system by resampling the micro-CT data onto planes orthogonal to the contact lines, allowing for vectors to be traced along the grain surface and the CO2-brine interface. A distribution of contact angles ranging from 35° to 55° is observed, indicating that the CO2-brine-carbonate system is weakly water-wet. This range of contact angles can be understood as the result of contact angle hysteresis and surface heterogeneity on a range of length scales. Surface heterogeneity is examined by comparison of micro-CT results with optical thin sections and SEM images.