Description
The main application of the Hybrid Directional Boring and Logging (HDBL) system is for cost-effective, high-quality access to an otherwise inaccessible contaminated subsurface (see figure below) for site characterization and sensor emplacement. The directional boring technology is an adaptation of existing hardware from various underground industries, primarily from the underground utilities industry. In the short-term development plans, the depths of the boreholes are somewhat shallow (50 ft), but long-term goals include greater well depths (80-100 ft), diameters (~6 in.) and lateral (horizontal) extents suitable for remediation purposes (400-1000 ft).
Hardware integrated for the directional boring facet of this technology includes wireline coring rigs, hydraulic thrust systems, electric cone penetrometers, steering tracking hardware, and push coring systems. Hydraulically activated thrust equipment capable of exerting more than 40 tons of thrust are used to push the directional boring heads into the earth. Directional control is obtained by proper positioning of the face of the nonsymmetric boring head. Slow rotation of the boring head will cut and compact the geologic material into the borehole wall. Thrusting a boring head that is not rotating will cause a directional change. The machinery is capable of initiating a borehole, steering down to a desired horizontal depth, continuing at that depth, and then steering back to the surface at a down-range location. This directional boring technology is desirable for environmental applications because the access method requires very minimal addition of fluids and very little soil removal during the drilling process.
Various logging and sampling technologies could be adapted, such as gamma and spectral gamma sensors, resistivity, mass spectrometry, fiber-optic fluorescence, pore pressure, fluid moisture, temperature, volatiles sampling (contaminant vapors), and a sidewall coring/soil sampling apparatus (second generation). In addition, various methods to emplace monitoring equipment are being developed including a pneumatic hammer technology for sleeve emplacement. A key function of the sampling hybrid system is to provide multiple discrete samples per run. It has the potential to recover pristine samples; moreover, it can be used to develop inexpensively a grid of horizontal wells (in an otherwise inaccessible subsurface) for contamination characterization, plume monitoring, and remediation verification.
Technical Performance Data
The Utilities Industry Rod Pusher is capable of exerting hydraulic, bidirectional thrust in excess of 80,000 lb and can be used in some soils with the standard solid rod and the Hogentogler cone penetrometer hollow rod. Rod diameters are 1.75 in. for both types.
Core Sampler. Provides a core 8-in. long and 1 in. in diameter.
Prototype Boring Machine. Hydraulic bi-directional thrust in excess of 80,000-lb, dry-bore compaction cutting for location/directional control.
Performance. In preliminary field testing, several directional holes were drilled; a depth of 40 ft was achieved with a maximum horizontal extent of 570 ft. Estimated costs were about $20 to $75/ft.
Pilot Scale Testing. Testing was performed as part of the Mixed Waste Landfill Integrated Demonstration at Sandia National Laboratories (SNL), Albuquerque, NM. The technology was also successfully used in the volatile organic compounds (VOCs) in Non-Arid Soils Integrated Demonstration in Savannah River, SC. Testing of directional boring for monitoring equipment installation was performed at the Savannah River Site (SRS) in an actual contamination zone during the summer 1992.
The hole was cased with a 3-in. fiberglass casing, in coastal plain sediments. The drilling rate is dependent on the geology.
Projected Performance
The project goal is to drill to a maximum depth of 80 ft and to obtain a maximum horizontal reach of 1000 ft. Other goals are to log multiple discrete soil samples per run and to integrate various instrumentation and sensing packages into the boring hardware.
Waste Applicability
Practical depth is estimated at 80 ft, and maximum horizontal reach is estimated at 1000 ft. Several geophysical monitoring, fluid characteristics, and contamination analysis tools can be incorporated with the hybrid drilling hardware. Developers state that the drilling method is amenable to a wide range of soil geologies. The developers have also noted that this method may ultimately be limited to compactible soils, although hardrock air drilling may be an option for more difficult media.
Status
The hybrid directional drilling system is being developed from modified hardware for existing drilling equipment used in the underground utility industry. The first-generation hybrid equipment may be available from the developer/manufacturer in 1994. The availability of more advanced, second-generation equipment may follow the first-generation according to demand.
Regulatory Considerations
The secondary process waste of this drilling technology is kept to a minimum by using only a small amount of water for drilling and electronics cooling. Cuttings are compacted into the formation with very little returned to the surface. Various drilling and safety regulations apply depending on the type of contaminant in the soil.
Potential Commercial Applications
This technology was developed from existing underground utility installation technologies, so it may also be returned and approved for use in these industries. In addition, the environmental monitoring, sensing, and characterization applications are useful to many industries that may have a shallow contaminant plume. The hybrid technology can be used by many industries economically to characterize, remediate, or monitor the contamination.
Baseline Technology
A baseline technology might be any larger directional boring and drilling rigs adapted from the oil, gas, and river-crossing industries. The larger equipment technologies are much more expensive ($300/ft of cased well compared to $20 to $75/ft with (HDBL) for directional drilling applications and may not be appropriate for use at shallow depths.
Intellectual Property Rights
Both Department of Energy (DOE) and Charles Machine Works, Inc., have patents pending.
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References
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