The water contact angle in a system of brine (20 wt % CaCl2) and CO2 was measured on a smooth dolomite surface [root mean square (RMS) surface roughness of 45 rim] with both hydrophilic and hydrophobic behaviors as a function of the pressure (0.1, 5, 10, 15, and 20 MPa) and temperature (308, 323, and 343 K). The experimental results show that the contact angle of brine/CO2 increases slightly with the temperature when the dolomite surface is hydrophilic but, interestingly, reduces When the surface is hydrophobic. The results also illustrate that the brine/CO2 contact angles increase with increasing pressure: We interpreted the experimental observations using the concept of alteration in van der Waals potential (substrate surface chemistry) with thermodynamic properties,. including pressure and temperature.