Comparative analysis of capillary threshold pressure measurement techniques: mercury intrusion porosimetry vs. innovative measuring tool for carbon storage

Threshold pressure is a critical parameter in evaluating the capillary sealing capacity of rocks, especially in reservoir and caprock studies related to CO 2 storage and hydrocarbon recovery. In this research, we conducted a comparative analysis of two methods for measuring threshold pressure: the traditional mercury intrusion porosimetry (MIP), which operates under different fluid dynamics, and a new gas-water/brine system (e.g., CO 2 -water) using novel equipment. The new apparatus employs techniques to directly measure the threshold pressure by monitoring the displacement of water by gas, such as CO 2 , in core samples. This system is designed to more accurately replicate in-situ subsurface reservoir conditions by accounting for key parameters such as CO 2 -brine interfacial tension, and pressure. By directly measuring the point at which gas begins to displace water from rock pores, it provides a more realistic assessment of the threshold pressure for CO 2 sequestration projects. For example, in the case of Sample 1, the direct measurement under a confining pressure of 15 MPa resulted in a threshold pressure of 0.4 MPa. In contrast, mercury intrusion data converted for CO 2 drainage estimated the threshold pressure at only 0.1 MPa. Similarly, for Sample 2, the direct measurement yielded a threshold pressure of 0.24 MPa, while the MIP method indicated a significantly lower threshold of 0.05 MPa. These discrepancies underscore the limitations of mercury intrusion when applied to CO 2 -water/brine systems. Underestimation of threshold pressure can have significant consequences for the design and safety of CO 2 storage projects, as this parameter is essential to assess the sealing efficiency of the caprocks and determine the storage capacity.