Experimental investigation of low interfacial tension displacements in oil-wet, fractured micromodels
Creators: name: Mejia, Lucas
name: 0000-0003-3344-0777
Publisher: name: The University of Texas at Austin
Year: 2018
Subjects: Micromodel
Surfactant
EOR
Fractured
Oil-wet

description: The objective of this work was to determine, using a microfluidics platform, if surfactants that reduce interfacial tension would produce oil from oil-wet, fractured systems in both static conditions (where no injection was involved) and in dynamic conditions (where fluid was injected into the system). The hypothesis was that as surfactants reduce interfacial tension between oil and water in an oil-wet, fractured porous medium, forces of very small magnitude (hydrostatic force created by a brine column less than 10 centimeters high, or transverse viscous pressure gradients) should overcome capillary forces and desaturate oil from the porous medium. Experiments where an oil-wet rock core is immersed in surfactant solution have shown surfactants can desaturate oil from oil-wet cores. Flooding experiments where surfactant is injected into fractured cores showed that viscous pressure gradients can aid in oil production from these types of rocks. In this work, micromodels fabricated using advanced fabrication methods were used to visualize oil production from oil-wet, fractured systems. Glass micromodels were made oil-wet using alkyl-silanes and designed to have large permeability contrasts (&gt;1000) between the pore-grain array and the fractures. To measure the effect of wettability on production, micromodels were immersed in brine and surfactant solution baths while lying flat on a surface (to minimize gravity forces) and oil saturation was measured over time. After 31 days, no oil was produced from the micromodel immersed in brine, and about 50% was produced from the micromodel immersed in the surfactant solution. The effect of gravity forces was examined by immersing micromodels in brine and surfactant solution baths while positioned vertically. Minimal (4%) oil desaturation was observed in the brine-immersed micromodel while approximately 75% desaturation was observed in the micromodel immersed in surfactant after 10 hours. Finally, dynamic experiments were conducted where brine followed by the surfactant solution were injected directly into a high permeability fracture that had a pore-grain array adjacent to it. No matrix desaturation was observed for the water flood, while approximately 25% oil-desaturation from the matrix was observed after 1 PVI of the surfactant solution. Recovery using surfactants was fast (in the order of hours) for experiments with imposed forces (gravity, transverse viscous pressure drop), and slow (in the order of days/weeks) for experiments without imposed forces. After visualizing surfactant floods in oil-wet, fractured micromodels under different flow conditions (negligible gravity, gravity driven, injection driven) it was concluded that low IFT is needed in order to reduce capillary forces so that very small driving forces (like the pressure difference created by a water column 5 cm high) can displace oil out of the low permeability matrix. This process can be further enhanced by properly designing the properties of the microemulsion phase, such as the viscosity.