Two-phase flow through low permeability fractured tight sand porous media

The objective of this research was to obtain fundamental understanding of single- and two-phase flow through fractured low permeability porous media. To achieve this objective, a series of single- and two-phase flow experiments as well as numerical simulation of single- and two-phase flow through tight sand media were conducted.; The considered porous medium sample was slot-pore type tight sand from the Travis Peak Formation with permeability in microdarcy range and porosity of 7%. Nitrogen and water were used as the gas and liquid phases.; Single-phase experiments were conducted at different pressure drops and overburden pressures. They showed that the sample used is very sensitive to overburden pressure.; Pore size distribution measurements showed the existence of a wide range of pore size (from 0.4 to 400 nm) distribution for the slot-pore type tight sand medium. Moreover, the single-phase gas flow through the sample particularly at low pressure is of the Knudsen diffusion type. Thus, the gas molecules may slip at the wall of the capillary and the Klinkenberg formulation may be appropriate to describe the deviation from Darcy's law.; Two-phase flow experiments were conducted at constant overburden pressure of 3000 psig and different pressure drops. Our data showed that two-phase flow through the sample is mainly dominated either by gas flow or by water flow. Three imbibition and three drainage runs were performed at overburden pressures of 2000, 3000, and 4000 psig, respectively. The experimental data showed that the presence of a fracture in a low permeability porous medium is the key factor for enhancing the gas recovery from tight gas reservoirs. The presence of a fracture enhances the gas flow, not only due to the increase in overall permeability, but also due to the creation of different flow patterns which locally shifted the two-phase flow away from capillary force domination region. Furthermore, the fracture opening plays a significant role in enhancing flow due to both reconfiguration of connecting pores and joining of the non-connecting pores to the flow network.; A volume averaged mathematical model for two-phase flow of gas and water in low permeability porous media was developed. This three-dimensional, isothermal, transient two-phase flow model was solved using CFX-Flow3D computer code. Our model includes an experimentally based expression for the capillary pressure as a function of concentration of each phase. Darcy and non-Darcy expressions for water and gas phases, and an empirical expression of the relative permeability of each phase.; The calculated flow behavior was in general agreement with the experimental observations and measurements. Our calculations also showed that the gas flow is higher when the fluids flow through a low permeability zone followed by a high permeability zone. This means the presence of fractures in the bottom-hole zone of the production well significantly enhances gas production from tight sand reservoirs.