The critical porosity of tight sandstone: electrical property change based on pore structure and minerals

Porosity, which is an important petrophysical parameter of tight sandstone, is closely related to its electrical property under 100% brine saturation. In this work, core resistivity measurements were conducted under reservoir net confining stress with samples from Upper Permian tight sandstone to investigate its critical porosity. Meanwhile, TS, XRD and CEC analyses were implemented. Experimental results show that the change of electrical property with porosity is not clear unless putting 5% as a cut-off point of porosity. It is found that the contribution of brine to core resistivity is variable for different porosity and 5% is the key cut-off point. Considering that core electrical property is determined by pore structure and minerals, microstructure was studied, indicating that 5% is the demarcation point of porosity. Further, mineralogical composition and clay's extra conductivity were analysed, and the results correspond to the conclusion on the porosity of 5% drawn by core resistivity measurements. ...