A fractal irreducible water saturation model for capillary tubes and its application in tight gas reservoir

The existing experimental method of obtaining irreducible water saturation is not applicable for low permeability sandstone reservoir. To calculate the irreducible water saturation of tight sandstone reservoir accurately, an irreducible water saturation model suitable for hydrophilic rock is established by combining the capillary tubes model with the fractal theory. The influence of formation temperature and the critical capillary radius (maximum displacement pressure) on the irreducible water saturation is simulated. The results show that at a certain temperature, the smaller the critical capillary radius is, the lower the irreducible water saturation is. When the critical capillary radius is constant, the higher the formation temperature is, the lower the irreducible water saturation is. To verify the validity of the model, the new model is applied to the gas layer in tight sandstone reservoir of Xujiahe Formation in Sichuan Basin, the calculated data of the irreducible water saturation is compared with the wax sealing water saturation. The results show that compared with the irreducible water saturation calculated under experimental conditions, the calculation results of the new model are closer to the wax sealing water saturation on the condition that the effect of formation temperature and the maximum displacement pressure on the irreducible water saturation is considered. It is proved that the new model is applicable for accurate calculation of the irreducible water saturation of the gas layer in tight sandstone reservoir.