Najeeb Alharthy

Phase Behavior and Minimum Miscibility Pressure in Nanopores

Numerous studies indicate that the pressure/volume/temperature (PVT) phase behavior of fluids in large pores (designated “unconfined” space) deviates from phase behavior in nanopores (designated “confined” space). The deviation in confined space has been attributed to the increase in capillary force, electrostatic interactions, van der Waals forces, and fluid structural changes. In this paper, conventional vapor/liquid equilibrium (VLE) calculations are modified to account for the capillary pressure and the critical-pressure and -temperature shifts in nanopores. The modified VLE is used to study the phase behavior of reservoir fluids in unconventional reservoirs. The multiple-mixing-cell (MMC) algorithm and the modified VLE procedure were used to determine the minimal miscibility pressure (MMP) of a synthetic oil and Bakken oil with carbon dioxide (CO2) and mixtures of CO2 and methane gas. We show that the bubblepoint pressure, gas/oil interfacial tension (IFT), and MMP are decreased with confinement (nanopores), whereas the upper dewpoint pressure increases and the lower dewpoint pressure decreases.

Matrix-Fracture Interface Cleanup Protocol for Tight Sandstone and Carbonate Reservoirs

In tight sandstone and carbonate reservoirs, the hydrocarbon recovery is mainly governed by the matrix- fracture interface mass transfer efficiency. To improve the matrix-fracture interface mass transfer in tight sandstone and carbonate reservoirs, we propose the following protocol to clean up the matrix-fracture interface and improve hydrocarbon production: (1) Inject one of the following – CO2 followed by anionic or non-ionic surfactant, Anionic or non-ionic surfactant followed by CO2, miscible or near miscible CO2 gas, low concentration anionic or non-ionic surfactant. (2) Repeat the process when another cycle of treatment is needed. The same procedure can be applied into injection well to improve injectivity. The proposed cleanup protocol improves production because – wettability alteration, reduction of IFT, swelling of the oil leading to lower viscosity, and molecular diffusion among other thermodynamic effects– all acting at the matrix-fracture interface. To assess the proposed matrix-facture interface clean up protocol, IFT and contact angle measurements that mimic the proposed processes were conducted. Favorable wettability alteration of tight carbonate and sandstone crude-aged cores and oil-brine IFT reduction were observed.