Thermodynamic effects of cycling carbon dioxide injectivity in shale reservoirs

A review of recent developments in CO2 mobility control in enhanced oil recovery

Carbon dioxide (CO2) in enhanced oil recovery (EOR) has received significant attention due to its potential to increase ultimate recovery from mature conventional oil reserves. CO2-enhanced oil recovery (CO2-EOR) helps to reduce global greenhouse gas emissions by sequestering CO2 in subterranean geological formations. CO2-EOR has been exploited commercially over recent decades to improve recovery from light and medium gravity oil reservoirs in their later stages of development. CO2 tends to be used in either continuous flooding or alternated flooding with water injection. Problems can arise in CO2-flooded heterogeneous reservoirs, due to differential mobility of the fluid phases, causing viscous fingering and early CO2 penetration to develop. This study reviews the advantages and disadvantages of the techniques used for injecting CO2 into subsurface reservoirs and the methods adopted in attempts to control CO2 mobility. Recently developed methods are leading to improvements in CO2-EOR results. In particular, the involvement of nanoparticles combined with surfactants can act to stabilize CO2 foam, making it more effective in the reservoir from an EOR perspective. The potential to improve CO2 flooding techniques and the challenges and uncertainties associated with achieving that objective are addressed.

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Carbon Dioxide Applications for Enhanced Oil Recovery Assisted by Nanoparticles: Recent Developments

How the oil recovery in deep oil reservoirs is affected by injected gas types: A molecular dynamics simulation study

A novel system for reducing CO2-crude oil minimum miscibility pressure with CO2-soluble surfactants

Primary oil recovery from fractured unconventional formations, such as shale or tight sands, is typically less than 10%. The development of an economically viable enhanced oil recovery (EOR) techni...

A Literature Review of CO2, Natural Gas, and Water-Based Fluids for Enhanced Oil Recovery in Unconventional Reservoirs

Reactivity of CO2 with Utica, Marcellus, Barnett, and Eagle Ford Shales and Impact on Permeability

CO2 injection is a promising method for enhanced oil recovery (EOR) in unconventional shale reservoirs. In this work, we postulate that CO2 EOR may be improved by the dissolution of surfactants into CO2. Although CO2 is a relatively good solvent for oil, we show that CO2 and Eagle Ford oil are immiscible at compositions above 70 wt % CO2, even at pressures as high as 62 MPa. The presence of a CO2–oil interface at reservoir conditions indicates that the addition of a surfactant has the potential to improve oil recovery─via wettability alteration from oil-wet to CO2-wet, CO2–oil interfacial tension (IFT) reduction, or both. Three nonionic surfactants (branched tridecyl ethoxylate Indorama SURFONIC TDA-9, branched nonylphenol ethoxylate Indorama SURFONIC N-100, and linear dodecyl ethoxylate Indorama SURFONIC L12-6) were evaluated for CO2-solubility, shale wettability alteration, effect on CO2–oil IFT, ability to generate CO2–oil foams, and ability to increase oil extraction from Eagle Ford, Mancos, and Bakken shale cores. Each surfactant dissolved in CO2 up to 1 wt % at pressures and temperatures commensurate with CO2 EOR. CO2-dissolved surfactants did not significantly affect CO2–oil IFT or generate CO2–oil foams, but they did induce a dramatic change in the contact angle of an oil droplet on an oil-aged shale chip in CO2 from strongly oil-wet (11°) toward intermediate CO2–oil wettability (82°) (at 80 °C, 27.6 MPa). The branched tridecyl ethoxylated surfactant, SURFONIC TDA-9, afforded the highest oil recovery in core soaking experiments─75%, compared to 71% by pure CO2. Analysis of oil extracts by gas chromatography revealed that heavier oil components were produced when the surfactant was added to CO2. These results indicate that CO2-dissolved surfactants may increase oil recovery from shale by wettability alteration from oil-wet toward CO2-wet. 

Dissolving Nonionic Surfactants in CO2 to Improve Oil Recovery in Unconventional Reservoirs via Wettability Alteration

CO2-Soluble Surfactants for Enhanced Oil Recovery from Shale


 This study attempts to determine if the efficacy of CO2-based enhanced oil recovery (EOR) techniques for unconventional liquid reservoirs (ULRs) can be increased through wettability alteration by adding a dilute non-ionic surfactant to CO2. The use of surfactants to increase the water-wetness of rock surfaces has previously been shown to improve oil recovery during water-based hydraulic fracturing and waterbased EOR in ULRs. In this study, nonionic surfactants are dissolved in CO2 to attain analogous significant shifts in wettability toward CO2-philic and oil-phobic. This could provide another EOR mechanism for the CO2-based recovery of oil from unconventional formations.
 The solubility of a nonionic, water-soluble, surfactant (Indorama SURFONIC® TDA-9, an ethoxylated alcohol with a branched tridecyl, oil-philic tail and nine ethylene oxide groups in the hydrophilic head group) in CO2 has been measured between 25 – 100 °C. This surfactant exhibits a solubility of roughly 1 wt% at pressures of 2000 – 5000 psia, with lower pressures required for lower temperatures.
 Eagle Ford outcrop samples were first aged in dead Eagle Ford crude oil at high temperature to attain oilwet characteristics. The oil wetness of shale samples was verified by measuring contact angles of water droplets in air. Then the samples were immersed in CO2 or CO2-surfactant solution for 16 h at 4000 psi and 80 °C. Contact angle measurements were then performed to identify shifts in wettability. No substantial change in wettability were observed for samples exposed to CO2, however the samples exposed to CO2-surfactant solution revealed a significant shift toward water-wet.
 Two CO2 huff ‘n puff experiments were then conducted for small, oil-saturated shale cores at 80 °C and 4000 psi. Faster oil recovery (i.e. more oil recovery in the first cycle) and cumulative oil recovery of 73% (after 7 huff and puff cycles) were achieved for the core immersed in CO2-surfactant solution (0.7 wt% surfactant) compared to 78% recovery for the core immersed in pure CO2.
 Continuing tests will examine the effects of rock type, oil properties, temperature, pressure, surfactant type (oil-soluble vs. water-soluble ethoxylated alcohols), surfactant concentration, and the presence of brine. CO2-soluble propoxylated alcohols will also be assessed because the polypropylene oxide oligomer is more CO2-philic than the conventional polyethylene oxide oligomer.

Lauren C. Burrows

Papers

A Literature Review of CO2, Natural Gas, and Water-Based Fluids for Enhanced Oil Recovery in Unconventional Reservoirs

Reactivity of CO2 with Utica, Marcellus, Barnett, and Eagle Ford Shales and Impact on Permeability

Dissolving Nonionic Surfactants in CO2 to Improve Oil Recovery in Unconventional Reservoirs via Wettability Alteration

CO2-Soluble Surfactants for Enhanced Oil Recovery from Shale

Laboratory-Scale CO2 Huff ‘n Puff EOR using Single Phase Solutions of CO2 and CO2 Soluble, Nonionic, Wettability Altering Additives