USA (Woodford Shale): Biological Enzymes for EOR in Shale

The ultimate recovery from shale formations is relatively low compared to the total in-place reserves — the U.S. Energy Information Administration puts the average recovery factor for Woodford shale at just 8.4%. That gap, combined with the shale's outsized role in future U.S. oil and gas production, is what drove researchers at the University of Oklahoma to test whether biological enzymes could move the needle where conventional EOR methods (gas injection, waterflooding, surfactant flooding) tend to struggle against shale's sub-0.1 mD permeability and nanometer-scale pore throats.

Methodology

The team ran spontaneous imbibition tests in Amott cells — a standard setup that measures how much oil a wetting fluid displaces from a crude-saturated core over time. Four Woodford shale outcrop cores (2 inches long, 1 inch diameter) were saturated with Texas crude via 72-hour pressurized injection at 1,500 psi after 24 hours of vacuuming — a slower, higher-pressure prep than sandstone requires, reflecting how much tighter the shale's pore structure is. Cores were then soaked in either deionized water (control) or a GreenZyme solution at 5 or 10 wt.% concentration. Two Berea sandstone cores were run in parallel as a higher-permeability reference point. Some of the shale samples were clay-rich, others carbonate-rich, based on FTIR mineralogy — the study found no significant difference in enzyme performance between the two rock types.

Results in Woodford Shale

In the shale cores, the 10 wt.% enzyme solution recovered 11% of oil in place after 360 hours, against 0% for the water control over the same window. The 5 wt.% solution performed even better in shale specifically — reaching 20-22% recovery after 200 hours, more than double the 12% for water. That makes 5 wt.% the more effective concentration for tight rock, even though it's the weaker solution: imbibition into shale is a slow, diffusion-driven process, and equilibrium in these cores took 200-360 hours to establish, roughly 2-3x longer than in the sandstone reference.

The more telling comparison for shale performance is against a non-ionic surfactant (a secondary ethoxylated alcohol) chosen to match the enzyme's surface tension. Run head-to-head in Woodford shale over 214 hours, GreenZyme at 5 wt.% recovered 20% of OOIP versus 15% for the surfactant, and visibly expelled more oil onto the core surface. The enzyme solutions measured 48.4 mN/m surface tension at 10 wt.% and 51.5 mN/m at 5 wt.% — notably higher than what the surfactant needed to hit a comparable range — which points to the enzyme working by altering rock wettability directly, "pushing" oil off the pore walls in these nanoscale throats rather than winning on interfacial-tension reduction alone.

Oil recovered from woodford shale using GreenZyme

Because enzymes act catalytically rather than being consumed in the reaction, their effect persists in the formation, continuing to invade shale's pores and fractures at lower concentrations well after the initial soak. That durability matters more in shale than in conventional rock precisely because imbibition is so slow there — a surfactant that adsorbs onto the rock and loses potency has a much narrower window to work in before the process stalls, while the enzyme keeps acting on oil-rock adhesion over the same drawn-out timeframe.

As a reference point, the same enzyme solution at 10 wt.% recovered 53% of oil in place from the Berea sandstone cores after just 123 hours, versus 2% for water — confirming the mechanism holds in conventional rock, though the shale results are the focus of this study given the formation's outsized role in U.S. unconventional production.

Conclusion

For Woodford shale specifically, the study identifies 5 wt.% as the more efficient enzyme concentration, outperforming both the 10 wt.% solution and a comparable surfactant over a realistic soak window. Oil recovery in shale via cyclic gas injection alone tops out around 10%; this work shows biological enzymes can push that recovery factor up to 25%, with an effect that keeps working in the formation long after treatment.

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Sources & Credits

Shadi Salahshoor, Sergio Gomez, Mashhad Fahes — The University of Oklahoma.

URTeC 2019-1117. Read the source →

This research was later patented — see US Patent 11,643,912, "Application of enzyme-based green solvents for the recovery of subsurface fluids," filed by Salahshoor in 2021.

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