Calculation of Reservoir Irreducible Water Saturation Based on NMR Experiment and Mercury Penetration Experiment

In order to calculate the irreducible water saturation of sandstone reservoir in a certain area in Xinjiang,142 sandstone rock samples are selected from six wells for experimental Nuclear Magnetic Resonance (NMR) and mercury penetration measurements.According to the result of NMR,using methods of T2 spectrum area ratio,weighing,Spectrum Bound Volume Irreducible (SBVI),unified T2cutoff,to get water saturation,it is seen that the weighing method and the T2 spectrum area ratio method are better,and the two methods are used to build irreducible water saturation model of sandstone reservoir in the study area.Based on NMR experiments measurements,all application conditions of irreducible water saturation derived from mercury intrusion capillary pressure experiments are studied.The studies suggest that for rock samples with the porosity of less than 15% and the permeability of less than 0.1×10-3μm2,the displacing force of 6.897×10-3MPa can drive all movable water,and that the water saturation derived from mercury penetration experiments is the true irreducible water saturation.For rock samples with porosity greater than 15% and permeability less than 0.1×10-3μm2,the displacing force of 6.897×10-3MPa can only drive some movable water,and the water saturation derived from mercury penetration experiments is not the true irreducible water saturation.Under the condition of reservoir with high porosity and permeability,the buoyancy generated by the difference of oil-water density in reservoir conditions which is equal to the capillary pressure in this paper,the water saturation obtained in pure oil conditions is the true irreducible water saturation.