NETL helped scientists at Montana State University evaluate microscopic cementing agents developed by the University that can more effectively penetrate microfractures to improve underground storage of carbon dioxide (CO2), enhance gas well efficiency and seal fluid pathways in shales fractured for natural gas recovery.
The research targeted use of a process called ureolysis-induced calcium carbonate precipitation (UICP), which produces a biomineral solution that can reduce undesired fluid flow. This could enable the more effective restimulation of previously hydraulically fractured shale formations and reduce flow through fractured rocks above storage formations.
The collaborative project involved researchers at Montana State, Lawrence Berkeley National Laboratory and NETL and was supported by EPSCoR, a National Science Foundation program that improves research competitiveness of targeted jurisdictions and a U.S. Department of Energy (DOE) program that supports Ph.D. thesis research.
UICP is a natural process that uses bacteria to break down urea — a colorless crystalline substance often used as a fertilizer, feed supplement and starting material for manufacture of plastics and drugs. Urea is produced in vast amounts when liquid ammonia and liquid CO2 are combined under high pressures and elevated temperatures to form ammonium carbamate, which then decomposes at much lower pressures to yield urea.
UICP is used to strengthen and stabilize soils, repair cracks in concrete, solidify heavy metals, and presents a viable opportunity to control permeability — a measure of the ability of a fluid or gas to pass through a material — in underground well bores and CO2 storage sites.
According to NETL’s Dustin Crandall, the biomineralization approach is an emerging biotechnology for subsurface engineering applications like remediating leaky wellbores. Researchers believe the process can also be effectively used in conjunction with hydraulic fracturing to increase recovery from shale gas wells by reducing fluid leak off through previously generated fractures.
A report co-authored by Crandall noted that “An abundance of natural gas is trapped within subsurface shale formations. Shale gas is an instrumental energy source and imperative to meeting global energy demands. Hydraulic fracturing, coupled with horizontal drilling, creates a fracture network within impermeable shale allowing access to otherwise inaccessible gas resources.”
NETL provided guidance and input on evaluating shale fracture sealing; provided fractured shale rock cores for experimentation; performed computed tomography scanning of selected shale cores; and hosted Montana State scientists to see the operations in the lab and help with image processing of scan data.
Crandall said hydraulic fracturing recovers only a small percentage of available hydrocarbons, leaving behind excess resources. Re-fracturing the rock can aid in enhanced resource recovery by extending the life and efficiency of an existing well. However, the re-stimulation method contributes new fractures.
“Sealing fractures will reduce undesired leakage pathways that may lead to a lack of restimulation, or undesirable migration of fluids from storage repositories.” Crandall said.
UICP offers an innovative solution to seal fluid pathways in fractured shale.
“Unlike common fracture filling materials, like cement, UICP is advantageous because it uses microscopic cementing agents, low viscosity fluids, non-toxic constituents, and can penetrate microfractures,” Crandall explained.
In addition to EPSCoR, the research is supported by DOE’s Office of Science Graduate Student Research Program (SCGSR) with a grant award that will enable a Montana State University researcher to come to NETL for five-months to conduct more extensive research on the UICP approach.
NETL is a U.S. Department of Energy national laboratory that drives innovation to deliver solutions for a secure energy future. Through its expertise and research facilities, NETL is advancing technologies to unleash America’s affordable, reliable and secure domestic energy and natural resources.
