Publications by authors named "Subhash Ayirala"

Understanding rock wettability is crucial across various fields including hydrology, subsurface fluid storage and extraction, and environmental sciences. In natural subsurface formations like carbonate and shale, mixed wettability is frequently observed, characterized by heterogeneous regions at the pore scale that exhibit both hydrophilic (water-wet) and hydrophobic (oil-wet) characteristics. Despite its common occurrence, the impact of mixed wettability on immiscible fluid displacement at the pore scale remains poorly understood, creating a gap in effective modeling and prediction of fluid behavior in porous media.

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Wettability plays a crucial role in multiphase fluid flow in porous media, impacting various geological applications such as hydrocarbon extraction, aquifer remediation, and carbon dioxide sequestration. Microfluidic methods have attracted interest for their capacity to explore and visualize essential multiphase flow dynamics at the pore level, mimicking actual rock pore structures. However, creating micromodels with representative mixed wettability is currently a challenge.

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Oil/water interfaces are ubiquitous in nature. Opposing polarities at these interfaces attract surface-active molecules, which can seed complex viscoelastic or even solid interfacial structure. Biorelevant proteins such as hydrophobin, polymers such as PNIPAM, and the asphaltenes in crude oil (CRO) are examples of some systems where such layers can occur.

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Enhanced oil recovery (EOR) from carbonates is obtained by injection of controlled ionic strength brines containing "active ions" (e.g., SO, Mg, Ca).

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In microfluidic studies of improved oil recovery, mostly pore networks with uniform depth and surface chemistry are used. To better mimic the multiple porosity length scales and surface heterogeneity of carbonate reservoirs, we coated a 2.5D glass microchannel with calcite particles.

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The treatment of produced water, associated with oil & gas production, is envisioned to gain more significant attention in the coming years due to increasing energy demand and growing interests to promote sustainable developments. This review presents innovative practical solutions for oil/water separation, desalination, and purification of polluted water sources using a combination of porous membranes and plasma treatment technologies. Both these technologies can be used to treat produced water separately, but their combination results in a significant synergistic impact.

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Article Synopsis
  • * The research measured interactions in chloride salt solutions across a broad concentration range (1 mM to 5 M) under different pH levels and temperatures, revealing that strong repulsive forces were present only at very close distances between surfaces.
  • * Instead of long-range electrostatic forces, the dominant interaction at distances of approximately 2 nm and beyond was found to be attractive van der Waals forces, with theoretical calculations confirming that the screening effect decreases as the concentration of ions increases.
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Wettability control of carbonates is a central concept for enhanced petroleum recovery, but a mechanistic understanding of the associated molecular-scale chemical processes remains unclear. We directly probe the interface of calcium carbonate (calcite) with natural petroleum oil, synthetic petroleum analogues, and aqueous brines to understand the molecular scale behavior at this interface. The calcite-petroleum interface structure is similar whether or not calcite was previously exposed to an aqueous brine, and is characterized by an adsorbed interfacial layer, significant structural changes within the calcite surface, and increased surface roughness.

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Article Synopsis
  • Field studies show improved oil recovery in high-salinity reservoirs when waterflooded with modified-salinity salt water (SmartWater), leading to beneficial changes in oil release.
  • This study focuses on the time-dependent physicochemical processes during diluted seawater flooding of carbonate reservoirs, assessing changes in wettability, surface roughness, and chemical composition.
  • Findings indicate rapid increases in oil/water/rock interactions occur within 15 minutes, while slower changes in rock surfaces take over 12 hours, enhancing water wetness and increasing oil recovery efficiency.
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Widely used traditional Parachor model fails to provide reliable interfacial tension predictions in multicomponent hydrocarbon systems due to the inability of this model to account for mass transfer effects between the fluid phases. In this paper, we therefore proposed a new mass transfer enhanced mechanistic Parachor model to predict interfacial tension and to identify the governing mass transfer mechanism responsible for attaining the thermodynamic fluid phase equilibria in multicomponent hydrocarbon systems. The proposed model has been evaluated against experimental data for two gas-oil systems of Rainbow Keg River and Terra Nova reservoirs.

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