Application of Nuclear Magnetic Resonance to Investigate Enhanced Oil Recovery and Geostorage of CO2 and H2

Abstract

The global energy transition demands innovative technologies to address growing energy needs while mitigating environmental impact. Nuclear Magnetic Resonance (NMR) relaxometry has emerged as a powerful tool for characterizing reservoir properties and fluid behavior, offering significant potential for applications in enhanced oil recovery (EOR), carbon capture and storage (CCS), and underground hydrogen storage (UHS). This study explores the capabilities of NMR in addressing the critical challenges associated with these energy transition technologies.First, NMR was applied to evaluate fluid recovery during Huff-n-Puff (HnP) EOR in shale reservoirs on preserved samples from the Eagle Ford and Wolfcamp using a mixture of C1:C2 (72:28) gas. Pressure stepped saturation using 2.5% KCl brine and dodecane was used to understand organic versus inorganic pore throats connectivity. Results show that oil production in Eagle Ford and Wolfcamp formations using C1:C2 (72:28) is primarily driven by the vaporization of lighter hydrocarbons (below C₁₃), while free water production is controlled by wettability and pore connectivity. The Eagle Ford formation exhibited continuous oil production (25% recovery) and moderate water recovery (15%), attributed to its well-connected organic pore network (pseudo parallel connectivity). In contrast, the Wolfcamp formation, characterized by high clay content (serial flow connectivity), showed limited oil recovery (10%) and higher water recovery (27%), with episodic water breakthrough after early oil production. These findings highlight the critical role of pore structure and connectivity in governing recovery behavior during EOR. For CCS applications, NMR was employed to assess the integrity of Class G cement exposed to supercritical CO₂ (scCO₂). The results showed that scCO₂ exposure led to precipitation and dissolution of calcium carbonate, leading to a reduction of porosity from 37% to 33% over five weeks. Notably, diffusional tortuosity increased sixfold after two weeks but later decreased to threefold after five weeks, suggesting an initial sealing stage followed by a dissolution phase. The extent of reaction was found to be pore-size dependent: in smaller pores (<30 nm), carbonate dissolution dominated, while in larger pores (30–200 nm), both precipitation and dissolution were observed. These findings indicate that scCO₂ exposure can alter the flow path in cement, potentially limiting CO₂ migration and leakage over time. In the UHS study, NMR was used to investigate hydrogen solubility in organic and inorganic bulk fluids. Experiments revealed that hydrogen remains primarily in the free phase in water and hydrocarbons, with negligible solubility observed in dodecane, dead oil, and ozokerite wax. However, fluorinert HT-230 (used as confining fluid for NMR plug measurement) exhibited measurable hydrogen solubility (4–6 cc of H₂ per 100 cc of fluorinert at 1800 psi). Additionally, long-term experiments in cyclohexane demonstrated progressive hydrogen dissolution over 32 days, increasing the hydrogen index (HI) by 3.42%, confirming slow but measurable uptake. These results highlight caution during signal processing and interpretation using hydrogen gas. Further, NMR was applied to assess hydrogen storage in rocks, including organic-rich shales (Eagle Ford, Duvernay, Marcellus) and partially brine-saturated Berea sandstone. Results indicated that hydrogen occupied the entire pore network in shales, with minimal interaction with the organics and clays, regardless of maturity. In sandstones, hydrogen storage capacity was also directly proportional to available pore space, with no significant hysteresis observed, confirming full recovery potential. Overall, this study demonstrates that NMR provides critical insights into fluid transport, phase behavior, and storage mechanisms relevant to EOR, CCS, and UHS. By quantifying fluid-rock interactions with high precision, NMR enhances our ability to optimize energy storage and recovery strategies in the subsurface, contributing to the development of sustainable energy solutions.