As a saturation logging evaluation problem, the conductance mechanism is studied with a tight gas reservoir in the Shihezi formation in Ordos Basin as an example, based macroscopically on the lithic quartz sandstone and the lithic sandstone, microscopically on the remnant intergranular pore and the corrosion intergranular pore, and combined with the thin section analysis data and the litho-electric experiment data. The relationships between the formation factor (F) and the porosity(φ), the resistivity index (I) and the water saturation (Sw)are affected by the lithology and the pore type. The conductance of the lithic sandstone is decreased because of the complexity of the mineral and pore type. Under the same condition, the formation factor and the resistivity index of the lithic sandstone are greater than those of the lithic quartz sandstone. The relationship between the resistivity index and the water saturation is exponential rather than as a specific power relation based on the numerical simulation of the network model. On the basis of the conductance mechanism, a modified Archie model of changeable cementation index is built for different lithologies and pore types. Applying the saturation model to this area, its practicability is confirmed.

tight sandstone gas reservoir  /  water saturation  /  conductance mechanism  /  improved Archie model