CAN001 – Pneumatic Fracturing
Sarnia, Ontario, Canada
Figure 1: KMnO4 Staining
In a joint research project between ARS and the University of Waterloo, Pneumatic Fracturing (PF) technology was used to increase permeability on fractured clay until deposit was investigated. This investigation involved a variety of hydraulic, tracer, and excavation experiments performed at five individual sites which were separately fractured by ARS’ patented fracturing process. In four of the sites, a single fracture injection interval occurred, targeting 2.5 m, 3.5 m, and 4.5 m below ground surface. A fifth site was developed with fractures targeting all of these zones within the same injection well. In addition, at one of the five individual sites where fracturing was applied at 4.5 m below ground surface, a potassium permanganate (KMnO4) tracer test was performed. The purpose of this test was to attempt to stain the fractures for visual tracing during a subsequent excavation. KMnO4 was selected as the tracer for its ability to react with the organic or reduced species in the clay, creating a very dark brown oxidation halo, very distinct from the surrounding gray matrix. A KMnO4 solution of approximately 5000 mg/L was injected at a rate of less than 1 L/hr for 21 days. A total of 187 L of solution was injected into the formation.
Single well response tests taken pre and post-fracturing show both local increases and decreases in hydraulic values, with increases as high as 4.7 orders of magnitude. The increases in hydraulic conductivity are a result of newly formed changes in the natural fracture network. Some minor decreases in hydraulic conductivity values that were observed are believed to be a result of deformation and consolidation of clay and natural fractures due to the fracturing process. Pumping rates (well yield), from pre to post-fracture conditions had increased from 0.05 L/hr to 4.1 L/hr, suggesting that there was an increase in bulk hydraulic conductivity due to the interconnection of the natural fracture network. The post fracture testing was performed approximately 8 months after Pneumatic Fracturing. A subsequent test, performed 10 days after the first, resulted in a reduced pumping rate of 2.7 L/hr suggesting that the newly opened fracture network may decrease slightly over time due to the pumping effects of overburden pressure. However, this pumping rate maintained a value two orders of magnitude greater than pre-fracturing conditions.
Figure 2: Results of KMnO4 Staining
The combination of KMnO4 staining and excavation indicated that three distinct fractures had propagated out radially as far as 91 cm from the fracture well in a spoke-like pattern along very discrete and tortuous vertical planes. These fractures terminated when natural fracture planes were encountered. Other, less discrete fractures may have existed but were not observable due to staining. KmnO4 staining of these planes, along with surface heave and pressure response data collected during the fracturing procedure indicate that the natural fracture apertures had been dilated. Subsequently, this allowed for an increase in fluid movement along these conduits.
- Field Performance Assessment of Pneumatic Fracturing for Permeability Enhancement of Clay Deposits, Steve Markesic – Master Thesis