Empirical Estimation of Sw from MudLog Gas, Viscosity, and GOR in Overbalanced, Normally Pressured Oil Reservoirs

This study presents an empirically derived formula for estimating water saturation (Sw) in oil reservoirs using surface logging data. Specifically, Sw is proportional to both mud log total gas analysis (TGA) and reservoir gas-oil ratio (GOR), and inversely proportional to drilling mud viscosity in overbalanced drilling systems. The approach enables real-time screening of reservoir productivity and early evaluation of reservoir quality where wireline data is limited or unavailable.