Multiple-contact Displacement Research Articles

Pore-Level Mechanisms of Residual Oil Formation during Miscible Displacement

Miscible flooding of oil from porous sedimentary formations by the injection of high-pressure solvents incorporates a complex interaction of heterogeneity, fingering, multiphase flow, and phase behavior. The objective of this work is to identify porescale mechanisms that lead to formation of a residual oil saturation in so-called miscible floods in the absence of water shielding. Oil displacements are carried out in two high-pressure, two-dimensional, transparent micromodels, which are simplified analogs of porous rocks. Displacement mechanisms are visualized for different solvents. Results show that the interaction of bypassing and phase behavior can lead to an immiscible residual with so-called first-contact miscible solvents. An equimolar mixture of ethane, propane, and n-butane (C 2C 3C 4) recovers all the oil in one-dimensional flow, but can leave a nonzero residual in dead-end pores of micromodels. Ethane develops multicontact miscibility with this oil in one-dimensional flow. Three hydrocarbon phases appear during the oil displacement by the methane-diluted equimolar mixture of ethane, propane, and n -butane. Capillary-driven flow recovers oil out of dead-end pores in ethane- and methane-diluted equimolar C 2C 3C 4 displacements. The interaction of viscous fingering and phase behavior can also contribute to miscible flood residuals in multiple contact displacements.

Multiple-Phase Generation During Carbon Dioxide Flooding

Abstract This paper describes research to determine the pressure and temperature region in which multiple phases are generated for selected reservoir oils displaced by CO2. The major purposes of this study were (1) to determine whether single-contact PVT conditions and multiple-contact flow generated multiple phases over equivalent pressures and temperatures, and (2) to determine whether multiple-phase generation would affect mobility. Multiple phases were generated for two reservoir oils of similar composition above the CO2 minimum miscibility pressures (MMP's) for temperatures between 307.5 and 322 K. For a limited temperature range, the pressures over which these multiple phases were observed agreed fairly well with those determined in single-contact PVT cell studies. However, multiple phases were also seen at higher temperatures in the multiple-contact displacements. Pressure-drop data as a function of CO2 injection volume were obtained for displacements within the multiple-phase region and for displacements conducted at pressures above the multiple-phase region. Comparison of these data indicates that multiple-phase generation reduces mobility within the flow system used. Mobility reduction would be beneficial during application of CO2 flooding on a reservoir scale.