OK002 – Pneumatic Fracturing
Federal Government Facility – Central Oklahoma
A pneumatic fracture well was installed in a semi-confined aquifer at a federal government facility contaminated with BTEX and TCE in central Oklahoma to enhance bioremediation. The site geology consisted of alternating layers of low permeability sandy silty shale underlain by a confining silty claystone aquifer. The selected remedial strategy was enhanced bioremediation.
Pneumatic Fracturing (PF) and Injection was selected to overcome low permeability within the treatment zone and its inherent anisotropy. However, there were concerns regarding the possibility of creating the vertical fractures and breaching the claystone aquifer.
Pneumatic injections were performed across the thickness of the aquifer. During fracturing, the target zone and areas beneath were monitored to detect any downward migration of fractures. The pilot test was conducted in February of 1995.
The post-fracture transmissivity in the fracture well increased five times after the field operation. Transmissivity values obtained from other wells with screen intervals across other smaller water bearing units exhibited smaller increases. Evaluation of the data revealed that Pneumatic Fracturing greatly reduced the anisotropy of the aquifer. This allowed water to be pumped from the aquifer at a higher rate indicating that the formation would be “dewatered” more quickly.
Fractures were not visible beneath the treatment zone indicating that the propagation was horizontal and none of the confining layers were breached. One exception occurred during a fracturing event: pneumatic pressure migrated to the gravel pack of a nearby well and traversed up the gravel pack and out into an upper water-bearing zone. The aerial influence of the pneumatic injection was demonstrated to be greater than 50 ft. from the injection well. Circulation of amendments to enhance bioremediation was accomplished in a more efficient and uniform manner with subsequent reductions in VOC concentrations.
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