Abstarct: The focus of this research is on measuring the contact angle of anhydrite cap rock samples, taken from the anhydritic facies of Qom Formation located in the Sarajeh gas field, when exposed to water-baxsed drilling mud with nanosilica additives in the presence of H2 gas. This essentially indicates the wettability of the rock. Wettability plays a significant role in the gas extraction process as it not only determines the initial fluid distribution but also impacts the sealing capability of the cap rock, its integrity, hydrogen recovery, and the chemical reactions between the cap rock and hydrogen. The contact angles obtained from the raw sample, the sample aged in water-baxsed mud, and the sample aged in modified mud at pressures of 15 psi, 300 psi, and 1000 psi, and a constant temperature of 50°C, range between 120 to 160 degrees. For cap rocks, water-wet conditions are preferred. Water-wet cap rocks have a strong affinity for water, which helps form a tight seal, preventing upward migration and escape of hydrogen from the storage site. This wettability ensures that the cap rock acts as an effective barrier and maintains the integrity of the storage reservoir. The contact angles measured by the captive bubble method showed that raw samples exhibit increased hydrophilicity with increasing pressure. Samples aged in baxse mud exhibited increased hydrophobicity over time and pressure, possibly due to chemical reactions between the mud and the anhydrite rock surface. Samples aged with nanosilica-modified mud showed increased hydrophilicity, indicating improved surface properties of the samples.