Multiscale visualization of chemical enhanced oil recovery
Chemical enhanced oil recovery (EOR) involves injecting chemicals such as surfactants, polymers, and alkalis into depleted oil reservoirs to increase oil recovery. Experimental tools such as corefloods and micromodels provide critical insights for the mechanistic understanding and screening of chemicals for EOR. Coreflood experiments are especially valuable for screening. However, imaging cores at high resolution for mechanistic understanding is challenging. Micromodels, synthetic optically accessible porous media that resemble rocks, address some of these challenges by allowing facile high-resolution imaging of displacements at the pore scale. However, they lack many important features of cores. In this work, we develop a novel micromodel, referred to herein as the Coreflood on a Chip, that permits visualization at the pore and core scales. Then, we investigate various forms of chemical EOR in the Coreflood on a Chip including viscous waterflooding, surfactant flooding, and alkali-surfactant-polymer flooding (ASP). Viscous waterflooding experiments were performed by injecting viscous glycerol solution or polymer solution into oil-saturated micromodels with irreducible water. We analyzed the experiments using fractional flow theory and pore-scale lattice Boltzmann simulations and found that irreducible water causes viscous fingering even at very favorable viscosity ratios. Additionally, we conducted corefloods to corroborate our findings translated to displacements in real rocks. Next, we performed surfactant and ASP floods by injecting aqueous chemical solutions with fluorescein into micromodels with oil and brine. This way, we could differentiate the injected aqueous phase from the resident aqueous phase. Our results prove that surfactants are present in and ahead of oil banks. Moreover, our results show that while saturations are well described by a fractional flow solution with two curves, aqueous phase concentrations are not properly described by said model because injected aqueous phase is present ahead of oil banks. Finally, we present a novel microfluidic device that can be utilized to conduct phase behavior salinity scans. We show the prototype microfluidic device is viable for performing salinity assays of crude oil-surfactant-water systems and segregation of microemulsion is visible in the device. In this work we demonstrate that evaluation of chemical EOR across scales permits identifying causal relationships between pore-scale processes and previously unobserved core scale behavior.