Understanding how fluids migrate through underground rock formations is essential for securely storing carbon dioxide ($CO_2$), managing groundwater resources, or cleaning up contaminated soils. A key parameter in this context is the capillary pressure, the pressure difference between two immiscible fluids, such as water and $CO_2$, in the pore space of rocks. However, reliable measurements of capillary pressure under realistic subsurface conditions are still limited.

Capillary pressure–saturation relationships were determined using the porous membrane technique within a custom-designed experimental platform SEPP (System for Experimental PetroPhysics) developed at GFZ Helmholtz Centre for Geosciences. Measurements were conducted during both drainage and imbibition cycles under pressure and temperature conditions relevant for subsurface $CO_2$ storage reservoirs. SEPP enables integrated acquisition of key petrophysical parameters, including hydraulic, electrical, and elastic properties. This data publication presents two datasets capturing capillary pressure, electrical resistivity, and P- and S-wave velocities from tests on two distinct sandstone samples.