Experimental Studies of NMR Logging Irreducible Water Saturation

54 sandstone rock samples are selected from Xujiahe Formation in Sichuan Basin for experimental nuclear magnetic resonance(NMR) measurements.Irreducible water saturation is determined through methods of T2 spectrum area ratio,weighing,SBVI,unified T2cutoffand comprehensive statistical parameter model.Contrast analysis of the five methods reveals that bound water saturation can be established on the basis of weighing method and T2 spectrum area ratio method,and that two methods of unified T2 cutoff value and comprehensive parameter statistical model are better than SBVI method,and can be used to determine Irreducible water saturation model of Xujiahe Formation in Sichuan Basin.According to mercury intrusion capillary pressure measurements,all the application conditions of irreducible water saturation derived from NMR experiments are studied.The studies suggest that as to rock samples the permeability of which is greater than 1×10-4μm2,displacing force of 0.6897 MPa can drive all movable water,and that irreducible water saturation derived from NMR experiments is the proper one.While for rock samples with permeability less than 1×10-4μm2,diplacing force of 0.6897 MPa can't drive all movable water,and irreducible water saturation derived from NMR experiments can only be the one under certain driving conditions.