Typical Sequence of Operations for Creating Hydraulic Fractures
Hydrofracturing is a pilot-scale technology in which pressurized water is
injected to increase the permeability of consolidated material or relatively impermeable
unconsolidated material. Fissures created in the process are filled with a porous medium
that can facilitate bioremediation and/or improve extraction efficiency. Fractures promote
more uniform delivery of treatment fluids and accelerated extraction of mobilized
contaminants. Typical applications are linked with soil vapor extraction, in situ
bioremediation, and pump-and-treat systems.
The fracturing process begins with the
injection of water into a sealed borehole until the pressure of the water exceeds the
overburden pressure and a fracture is created. A slurry composed of a coarse-grained sand
and guar gum gel or a similar substitute is then injected as the fracture grows away from
the well. After pumping, the sand grains hold the fracture open while an enzyme additive
breaks down the viscous fluid. The thinned fluid is pumped from the fracture, forming a
permeable subsurface channel suitable for delivery or recovery of a vapor or liquid.
The hydraulic fracturing process can be used in conjunction with soil vapor extraction
technology to enhance recovery. Hydraulically-induced fractures are used to deliver
fluids, substrates and nutrients for in situ bioremediation applications.
The cost per fracture is estimated to be $1,000 to $1,500, based on
creating four to six fractures per day. This cost (including equipment rental, operation,
and monitoring) is small compared to the benefits of enhanced remediation and the reduced
number of wells needed to complete the remediation. A number of factors affect the
estimated costs of creating hydraulic fractures at a site. These factors include physical
site conditions such as site accessibility and degree of soil consolidation; degree of
soil saturation; and geographical location, which affects availability of services and
supplies. The first two factors also affect the effectiveness of hydraulic fracturing.
costs presented in this analysis are based on conditions found at the Xerox Oak Brook
site. A full-scale demonstration was not conducted for this technology. Because operating
costs were not independently monitored during the pilot-scale demonstrations at the Xerox
Oak Brook and Dayton sites, all costs presented in this section were provided by Xerox and
University of Cincinnati Center Hill.
Technologies: Field Scale Demonstration Project in North America,
of Remediation Case Studies, Volume 4, June, 2000, EPA
EPA, 1991. Feasibility of Hydraulic Fracturing of Soil to
Improve Remedial Actions, EPA/600/S2-91/012.
Guide to Documenting and Managing Cost and Performance Information for
Remediation Projects - Revised Version, October, 1998, EPA 542-B-98-007
EPA, 1993. Hydraulic
Fracturing Technology, EPA/600/R-93/505.
EPA, 1993. Hydraulic Fracturing of Contaminated Soil, series
includes Demonstration Bulletin, EPA/540/MR-93/505; Technology Evaluation and Applications
Analysis Combined, EPA/540/R-93/505; and Technology Demonstration Summary,
EPA, 1994. In Situ
Remediation Technology Status Report: Hydrofracturing/Pneumatic Fracturing, EPA/542/K-94/005.
EPA, 1997. Analysis
of Selected Enhancements for Soil Vapor Extraction, EPA OSWER,
Federal Remediation Technologies Roundtable, 1997. Remediation Case
Studies: Soil Vapor Extraction and Other In Situ Technologies,
Hubbert, M.K and D.G. Willis, 1957. "Mechanics of Hydraulic Fracturing,"
Petroleum Transactions AIME, Vol. 210, pp. 153 through 168.
Murdoch, L.C., 1990. "A Field Test of Hydraulic Fracturing in Glacial Till,"
in Proceedings of the Research Symposium, Ohio, EPA Report, EPA/600/9-90/006.
Murdoch, L.C., 1993. "Hydraulic Fracturing of Soil During Laboratory
Experiments, Part I: Methods and Observations; Part II: Propagation; Part III: Theoretical
Analysis", Geotechnique, Vol. 43, No. 2, Institution of Civil
Engineers, London, pp. 255 to 287.
University of Cincinnati (UC), 1991. "Work Plan for Hydraulic Fracturing
at the Xerox Oak Brook Site in Oak Brook, Illinois".
Wolf, A. and L.C. Murdoch, 1992. "The Effect of Sand-Filled Hydraulic
Fractures on Subsurface Air Flow: Summary of SVE Field Tests Conducted at the Center Hill
Research Facility", UC Center Hill Facility, Unpublished Report.