CO2 Utilization with Complexation of Polyelectrolyte Complex Nanoparticles and Surfactants for Environmentally Friendly Unconventional Oil Recovery: Mechanistic Study, Recovery and Multiscale Visualization

Abstract

Despite the imbalance in supply and demand of energy, due to the pandemic caused by the spread of coronavirus, the energy sector is experiencing a historic boost in oil and natural gas production thanks to development of hydraulic fracturing for unconventional recovery from tight shale formations. However, the process suffers from large dependency on water resources with reported negative environmental impacts. Reduction of freshwater use in hydraulic fracturing via high internal phase emulsions (foams) is a promising approach help to protect the quantity and quality of drinking water resources, to reduce the volume of water requiring disposal and, where deep well injection is the means of disposal, to reduce the risk of causing seismic activity. A sustainable approach for reduction of freshwater consumption and produced water disposal is to inject water-less fracturing fluid with minimum aqueous phase volumes prepared using water obtained from the production cycle itself. The main objective of this work is to generate a stabilized supercritical CO2 (scCO2) foam using produced water and to study its texture, investigate its interactions with oil, and to use multiscale observation techniques to correlate foam microstructure with its stability and oil recovery performance in an environmentally friendly unconventional oil recovery process. Application of compressed CO2 foam provides enough viscosity for hydraulic fracturing and improves oil production while also serving as a promising CO2 storage and sequestration method in shale formations. The mixture of produced water and compressed CO2 in supercritical state was stabilized to form homogenous scCO2 foam. Two oppositely charged polyelectrolytes were dissolved and mixed in produced water to generate Polyelectrolyte Complex Nanoparticle (PECNP) that in turn helped form a stable lamella between the aqueous phase and the scCO2 while degrading in the presence of crude oil. The foam system improved fracture propagation, proppant transport, and fracture cleanup compared to the base case foam system with no PECNP. Enhanced bulk viscosity and improved foam quality as a result of complexation at the interface was identified with rheometry in addition to sandpack experiments with PECNP-surfactant ratios of 1:9 and 4:6, in 33.3 kppm and 66.7 kppm salinity brine systems, respectively. Formation damage was controlled by the newly introduced mixtures as fluid loss volume decreased across the tight Kentucky sandstone cores by up to 78% and 35% for scCO2 foams made with PECNP-WLMs in 33.3 and 66.7 kppm salinity brine, respectively. The formation of PEC-surfactant nanoparticles was verified via dynamic light scattering and transmission electron microscopy (TEM). A Raman spectroscopic model was developed to realize the structural changes associated with complexation. The possibility of molecular complexation for lamella stabilization was also explored for EOR application. Molecular complex containing PECNP and N-120 ethoxylated surfactant was employed to enhance scCO2 foams made with the thin film of high salinity brine formed between scCO2 bubbles and the formation of molecular complex improved DLVO forces in aqueous polyelectrolytes for carbonate surfaces. Millimetric view cell visualization was coupled with micrometric fluidic visualization to facilitate multi-scale observation of physical structure, geometry, dynamics and stability of electrostatically enhanced scCO2 foam. Multiphase flow in fractured medium was emulated using glass micromodels. Wet etching technique on glass was performed via UV photolithography and thermal bonding, whereas dry etching was conducted with selective laser etching (SLE) inside the bulk glass. Lamella stability as a result of complexation of two oppositely charged polyelectrolytes with zwitterionic surfactant was investigated and compared in the view cell and glass microchips.