Fluid Production Studies Using NMR and High-Frequency Dielectric Permittivity

Abstract

Abstract Fully water saturated plugs were centrifuged in air using small capillary pressure steps. At each pressure step the low frequency (2 MHz) NMR and high frequency dielectric permittivity were measured. The centrifugal pressure steps were incremented at 1 psi so as to determine the water saturation at fine scale. These experiments are designed to replace water by air, which has no NMR signal. As a result NMR signal decreases as the centrifugal pressure increases. The NMR T2 distribution data show gradual depletion of free water from the pore space as the centrifugal pressure increases from zero to five psi. Above this pressure the rate of fluid production per pressure decreases suggesting the produced water is bound to the pore wall. A plot of water filled porosity vs centrifugal pressure shows at least two regimes. An initial fast production at low pressures has a larger slope compared with later slow production at higher pressures. Both smaller produced volume and higher pressures are consistent with the water being bound to the pore surface. The dielectric permittivity also shows a decrease in permittivity as the centrifugal pressure increases. This is because the dielectric permittivity is most sensitive to the water content as compared to air or solid matrix. The permittivity data plotted vs the centrifugal pressure also show at least two different slopes. The initial fast slope is attributed to the production of free water while the higher pressure slow slope is due to bound fluid.