Multifunctional foams and emulsions for subsurface applications
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Foams and emulsions hold immense potential in assisting in the different stages of oil recovery processes such as enhanced oil recovery, drilling, and completion. This work is focused on developing robust, multifunctional foams or emulsions for subsurface applications, which offer unique advantages over conventional methods. The first half of the dissertation is focused on investigating novel foams stabilized using nanoparticles and/or surfactants to improve the gas enhanced oil recovery process. Gas flooding often has poor volumetric sweep efficiency due to viscous fingering, channeling, and gravity override. Foam is a promising tool to improve sweep efficiency in gas floods. It can reduce the mobility of gas by several orders of magnitude by increasing its apparent viscosity while keeping the liquid phase mobility unchanged. For sandstone reservoirs, which are typically water-wet in nature, two different approaches of foam stabilization using nanoparticles were developed. In the first approach, synergistic stabilization of foams with a mixture of hydrophilic nanoparticles and an anionic surfactant was investigated. Foam stability experiments in bulk and porous media tests showed that adding hydrophilic nanoparticles to surfactant formulations increases the foam stability. Microscopy revealed that nanoparticles are trapped in lamellae as well as at the Gibbs-Plateau borders. These nanoparticles act as physical barriers and retard the liquid drainage and the Ostwald ripening process. To fundamentally understand the role of nanoparticles in altering the foam dynamics in porous media, a high-pressure visualization experiment was performed in a 2D layered, heterogeneous porous media. This experiment showed that immiscible foams can result in significant incremental oil recovery of 25% to 34% OOIP (over waterflood). In the second approach, foam stabilized using in-situ surface-activated nanoparticles without any surfactant was explored as an EOR agent. The surface chemistry of the hydrophilic nanoparticles was tailored by adsorption of a small amount of short-chain surface modifiers to obtain surface-modified nanoparticles (SM-NP). Foam stabilization using these SM-NP was compared with that using a conventional surfactant to evaluate the potential of these SM-NP to act as an effective foaming agent. Carbonate reservoirs, which are typically highly heterogeneous and oil-wet in nature, pose additional challenges for an effective foam EOR process. Crude oils are typically detrimental to foam stability. An oil-wet carbonate will have a thin oil film on the surface and thus foam lamellae stabilization is challenging. Therefore, wettability-alteration of rock matrix toward water-wet condition using a surfactant is required to favor the in-situ foam stability. This work demonstrated for the first time a synergistic approach of using foams with wettability-altering capabilities for oil-wet systems. It was shown that optimal surfactant formulations can not only alter the wettability of a carbonate core from oil-wet to water-wet conditions, but also can significantly increase the in-situ foam stability even in presence of crude oil. The second half of the dissertation is focused on developing novel microencapsulation techniques using the concept of water-in-air powders for subsurface applications. A facile, one-step method was reported to encapsulate micro- or nano-sized hydrophilic particles using silica nanoparticles. The encapsulated particles can be released based on an external stimulus, such as a change in pH of the external continuous phase. The use of this novel carrier system was demonstrated for the delayed release of PPG particles for conformance control. The application of this technology was then explored for microencapsulating highly concentrated acids (~10 wt.% HCl) for acid treatment of shales. The advantages of these novel acid-in-air powders over conventional acid-in-oil emulsions (which are typically used for shale acidization processes) were illustrated in terms of the thermal stability, corrosion inhibition efficiency, and shale surface reactivity.