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Underwater Directional Bore Tracker


OBJECTIVE: The objective is to develop a simple Horizontal Directional Drilling (HDD) tracking tool that works underwater in the near-shore and surf zone. Accurate tracking is critical to make sure the drill is guided to the proper exit point and the utility survives for its planned service life as well as being environmentally benign. DESCRIPTION: Naval Facilities Engineering Command (NAVFAC) uses HDD for cables and utilities to cross under the aggressive and hazardous zone at the sea-shore interface. Horizontal Directional Drilling has become common practice for routing utilities and communications cables under waterways and under the sea-shore interface. HDD minimizes environmental impacts and eliminates the risk of abrasion and damage from heavy wave forces or damage from anchors and dredging. The ability to track and guide the HDD drill head is important for environmental and survivability concerns. Accurate tracking is critical to make sure the drill is guided to the proper exit point and the utility survives for its planned service life. In addition, accurate tracking minimizes the environmental risk of an excessive release of drilling mud into the ocean. A robust low-frequency hand-held diver-operated tracking system is needed that works underwater with small HDD systems used by the Navy. The technology to guide and track an HDD drill string is well developed for terrestrial applications. The most accurate HDD tracking systems incorporate a wire-line system using DC magnetic field and a sensor grid placed on the surface. This type of system can be costly and requires specialized training to operate. Placement and survival of a grid system is difficult or impossible in the surf zone. In addition, wire-line tracking systems do not work for smaller HDD systems used by the Navy. Another commercial technology used for tracking is a walkover system, which does not use a wire-line, but relies on a battery operated transmitter placed in the drill head. However, walkover systems operate at frequencies that are range limited and can be disrupted by conductive media. Commercial walkover systems do not work underwater. PHASE I: Develop a concept and fabricate a small laboratory device for testing. The sensing detector would be a battery-operated hand-held unit that works underwater when operated by a diver. The transmitter would also be battery-operated and placed inside the drill head, and would transmit low-frequency AC"tones"less than 100 Hz. The system should be capable of measuring signal strength and direction at ranges of 50"to 100"through the earth and water. The detection device must accurately detect the transmitter unit with an accuracy of +/-5% of slant range. This innovative system must be impervious to adjacent conductive media, such as other pipelines and cables. Multiple frequencies and selectable frequency options shall be considered. Remote frequency control of the transmitter shall be considered as a feature. Research shall include analysis of optimal frequency or combination of frequencies for underwater tracking. PHASE II: Build and demonstrate the Phase I detection and transmission system and test it in a near relevant environment. The prototype should be modified based upon testing and altered prior to field testing. PHASE III: Build and validate a system that can be fielded and operated as intended. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Commercial electric and gas utilities, telecommunications, seawater intake, oil and gas pipeline. REFERENCES: 1. Directionally Drilled Bores For Remote Cable Landings, Sinclair, Nate et al, NAVFAC Engineering Service Center, 1 Sept 2003. 2. Horizontal Directional Drilling (HDD) Systems for Pilot Bore Drilling in Mixed Soil Conditions and Rock, Gerald A. Strangl,
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