ABSTRACT
While global energy demand is increasing at an exponential pace, oil-alternative fuel sources have been unable to match the supply needs. This renders us dependent on hydrocarbons to fulfill our energy needs for the immediately foreseeable future. However, the burning of hydrocarbons releases copious amounts of CO2, which in the atmosphere, causes global warming. These twin challenges can be tackled by implementing combined enhanced oil recovery (EOR) and carbon sequestration projects. Any process that alters the property of the reservoir fluids or rock to further improve hydrocarbon recovery is known as EOR while carbon sequestration involves the injection of atmospheric carbon down into the subsurface, where it would be unable to play any role in further aggravating global warming. However, the combined implementation of EOR and carbon sequestration is plagued with unique challenges that can only be countered by synthesizing and improving the properties of carbon-based nanomaterials like carbon nanotubes (CNTs).
Given their superior properties like high conductivity, mechanical strength, and superior aspect ratios (length/diameter ≥1000), which are highly relevant in subsurface applications, CNTs have elicited a great interest amongst researchers who have explored the use of single-walled CNTs (SWCNTs) and multi-walled CNTs(MWCNTs) for oilfield applications. These CNTs are dispersed in varying base-fluids to form colloidal suspensions (nanofluids), which are then used for field application. Past studies have proven that CNTs reduce the interfacial tension (IFT) between oil/water while mixing CNTs with acidic oil forms an in-situ surfactant, enabling the lowering of the capillary pressure within the small pore increasing crude oil recovery. It is hypothesized that the in-situ surfactant would also form foam with injected CO2, reducing its mobility leading to the formation of a uniform front and increasing the carbon storage potential of the reservoir. However, for the application of CNTs in the combined processes (EOR and carbon sequestration) to succeed, various factors like reservoir temperature, pressure, salinity, and heterogeneity would have to be accounted for and understood. Hence, the chapter would aim to elaborate and explain, in detail the application of CNTs in EOR and carbon sequestration under prevalent reservoir conditions to promote a carbon-negative future.
