“Primary recovery from hydraulic fracturing in these unconventional formations is typically between 3% and 10% of oil in place and 5% to 30% of natural gas in place,” said NETL researcher Angela Goodman, a world-renowned expert in geological systems.

“Our task involves finding safe and cost-effective strategies to recover far greater percentages of the oil and gas left behind in those reservoirs.”

The research team claims that the nuclear magnetic resonance (NMR) spectroscopy provides valuable assistance.

The NETL team is using NMR technology to quantify fluids in subsurface cores by determining the porosity and pore size distribution for pores as small as 1 nanometer. NMR can also identify the type of fluid in the core by differentiating fluids of different viscosities, such as water, hydrogen, heavy oil, light oil, and natural gas, and characterize a core’s wetting properties to determine whether the rock will preferentially take up water, oil, natural gas, and carbon dioxide (CO2) to promote oil and gas recovery, according to a press release.

“We begin with saturating shale cores in hydrocarbon oil. Hydrogen atoms are abundant in the hydrocarbon-soaked cores. When the rock core is placed in the NMR unit’s magnetic field, the hydrogen nuclei align themselves with the field,” said NETL researcher Matthew Grindle. 

Researchers revealed that a radiofrequency pulse is then applied, briefly knocking the nuclei out of alignment. Once the pulse is switched off, the protons slowly return to their magnetically aligned state in a process known as “relaxation.”

NMR relaxation times provide information about in-situ porosity (percentage of void space within a rock indicating how much water, oil, or gas it can hold), pore size distribution (size of pores within a rock), permeability (a measure of how easily fluids can flow through the interconnected pore spaces within the rock), and fluid saturation of the rock, as per the release.

Researchers also revealed that the NMR unit has the capability to analyze rock cores while in a pressure vessel to simulate extreme pressures of up to 10,000 psi and temperatures of 100 degrees Celsius, which are found in the subsurface, and study how fluids flow through rock cores under these conditions.

“Such analyses enable the measurement of initial multiphase fluid saturation (water, hydrocarbons, etc.) and monitor fluid saturation changes throughout injection of new fluid such as CO2, natural gas, water, and surfactants intended to initiate oil recovery” said NETL researcher Lauren Burrows.

The NMR technology will be used to conduct experiments in which the oil-saturated rock core is held at high pressure and injected with natural gas, water, surfactant, or CO2 to complete a technique known as “huff-and-puff.”

During these huff-and-puff experiments, digital scans are generated to create a 3D map of the distribution of fluids in the rock and show how the injected fluid moves the oil and water throughout the rock pores, including fluid in nanopores that are thousands of times smaller than the width of a human hair, according to the press release.