Frakturering

Summary and conclusions

Fracturing is a method whereby a gas (pneumatic fracturing) or water / slurry (hydraulic fracturing) is injected into the subsurface at pressures exceeding the natural in-situ pressure in the subsurface (i.e. overburden pressure, cohesive stresses, etc.) and at flow volumes exceeding the natural in-situ permeability. The induced fracture itself is commonly a sheet like feature with maximum dimensions of roughly 20 meters and a thickness of 1 to 20 mm depending on the type of injection fluid used. Hydraulic fractures are commonly filled with granular material which serves to prop the fracture open. Pneumatic fractures are not filled with granular material and are kept open due to irregularities along the fracture walls.

Investigations over the past 10 years in North America have shown that fractures can be created in contaminated, fine-grained sediments, where they increase flow rates to and from wells by one or two orders of magnitude. The technique appears to offer the possibility of significantly reducing the costs of remediating contaminated sites underlain by silty clay till by increasing the rate at which remediating agents can be introduced to the subsurface and the rate at which contaminated fluids can be extracted.

The objectives of this study are:

1. to carry out a state-of-the-art literature review of the fracturing techniques
2. to evaluate the applicability of hydraulic and pneumatic fracturing under typical geologic conditions in Denmark
3. to evaluate the feasibility of creating hydraulic fractures at the Haslev field site in Denmark

The literature study was prepared in collaboration between Bertel Nilsson (senior author) at Geological Survey of Denmark and Greenland, Claus Gormsen and Birger C. Blem at NIRAS (Danish consulting company) and the developers of the hydraulic fracturing technique for environmental applications Dr. Bill Slack at FRx, Cincinnati, OH, US (American fracturing company) and Dr. Larry Murdoch, Clemson University, SC, and president of FRx. The study is financed by the Danish Environmental Protection Agency , Danish EPA (DK: Miljøstyrelsen).