NETL Research To Boost Oil and Gas Production by Maximizing Production in Tight Formations

Researchers at NETL are working to significantly increase the volume of oil and natural gas that can be recovered from unconventional formations, where only a small percentage of hydrocarbons in place are typically extracted, to ensure affordable, reliable, and secure energy for the United States.

NETL's research focuses on recovering these additional resources in shale and other tight reservoirs that have already produced hydrocarbons through hydraulic fracturing in primary recovery operations but still contain large amounts of oil and gas trapped within rocks.

"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. Our task involves finding safe and cost-effective strategies to recover far greater percentages of the oil and gas left behind in those reservoirs," said NETL researcher Angela Goodman, a world-renowned expert in geological systems.

That's where 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.

"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.

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.

The Lab's 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.

The information tells researchers if this enhanced recovery technique will drive hydrocarbons from the pores of a rock core toward the wellbore.

In addition, the scans can show if fluid is moving in pores in the center of the rock, along the edge of the rock, or in pores located next to clay or organic material. "Such insights will expand the knowledge base into the complex interactions between fluids and rock formations, making NMR an important resource for enhanced oil recovery (EOR) research," Grindle said.

Other benefits of undertaking NMR studies include tracking the ability of surfactants to change the wettability of oil-bearing rock. Wettability is the tendency of a fluid to spread on or adhere to a solid surface. Surfactants increase EOR by changing the wetting properties of the rock, allowing oil to flow more freely from pores.

Injecting rich natural gas, characterized by a higher concentration of heavier hydrocarbons, increases the mobility of the trapped gas and a more efficient displacement of the remaining hydrocarbons toward production wells, thereby enhancing total recovery.

"NETL is pioneering the use of this technology within the U.S. Department of Energy's national lab system to build upon our expertise in unconventional oil and gas production and provide the breakthroughs we need to develop energy for the American people," Goodman said.

NETL is a U.S. Department of Energy (DOE) national laboratory dedicated to innovating and accelerating the nation's energy solutions in hydrocarbons, geothermal energy, and critical minerals production. The Lab further strengthens its impact by engaging with industry, academia and other stakeholders through four strategically located Centers of Excellence: Coal, Critical Minerals and Advanced Alloys, Oil & Gas, and Geothermal. With research sites in Albany, Oregon; Morgantown, West Virginia; and Pittsburgh, Pennsylvania, NETL operates as one laboratory to create advanced energy technologies that support DOE's mission and enable affordable, reliable and secure energy to fuel human prosperity.