Abstract: During oil and gas well drilling operations, at the wellsite surface the percentage by volume of hydrocarbon gas present in the return drilling fluid is monitored in order to determine the percentage of gas saturation in the formation. Rate of penetration of the drill bit is monitored as well. A pore saturation function is derived wherein anomalously low values thereof relative to expected values for productive zones indicate flushing ahead of the drill bit of hydrocarbons out of the pore volume of cuttings in the return fluid. A mud filtrate flow rate is then determined from the drilling rate, gas saturation, and formation porosity. Pressure differential in the vicinity of the drill bit is also determined, comprised of the difference between the drilling fluid column pressure and pore pressure. Formation permeability is then directly determined in real time during the drilling operation from a functional relationship between the filtrate flow rate, pressure differential, and viscosity of the drilling fluid.

Abstract: During oil and gas well drilling operations, drilling fluid volume circulated per preselected vertical borehole increment drilled is continuously measured as well as the percentage by volume of hydrocarbon gas present in the return fluid. The gas is periodically sampled and analyzed to derive a relative ratio of C.sub.1 and C.sub.2 present therein. A functional relationship is then periodically computed relating the drilling fluid volume circulated per vertical increment drilled, and percentage of hydrocarbon gas therein, the rock volume of cuttings from which the gas evolved, and borehole pressure and temperature conditions at which each mud sample received respective cuttings to provide a percentage gas saturation parameter per vertical foot of reservoir. In functional response to the C.sub.1 /C.sub.