Abstract
Unconventional gas resources will significantly affect the future of the energy sector worldwide in the coming years. The importance of non-Darcy flow has been highlighted in the literature in the context of highly productive fractured gas wells. The low gas flow rates from typical tight gas wells contradict this assumption. Neglecting the non-Darcy flow effect in tight reservoirs will lead to an overestimation of production and other misleading facts about tight gas reservoirs behavior. The interpretation of deviation from Darcy's flow through tight sand porous medium is addressed, in this work, by conducting a series of single phase gas flow experiments. The considered porous medium sample was slot-and-solution pore type tight sand collected from the Travis Peak Formation at a depth of 2654 m with permeability in microdarcy range and porosity of 7%. Two gases, nitrogen and helium, were used. Single-phase gas experiments were carried out at different pressure drops and overburden pressures. The experimental results showed that the examined slot-and-solution tight sand porous media is very sensitive to overburden pressure. Pore size distribution measurements, by mercury intrusion porosimetry and sorption isotherm, showed the existence of a wide range of pore size distribution (from 0.4 to 400 nm). The analysis shows that single phase gas flow through tight gas sand particularly at low pressure is of Knudsen diffusion type. Thus, the gas molecules may slip at the wall of the capillary and the Klinkenberg formulation may be the approach to describe the deviation from Darcy's law when the pore size and particle size are almost the same.
