Use of Downhole Instrumentation to Reduce Risk of Inadvertent Return (“Frac-Out”)

For a large-scale, multi-phase cable installation located in central Maryland, HDD has been used to install new duct bundles to reduce surface disturbance associated with open-cut construction. Complex geologic conditions and excessive downhole pressures have caused significant fracouts (inadvertent returns) during previous project phases, resulting in excessive cleanup costs and permitting delays. To reduce this risk, the project team has implemented a comprehensive instrumentation program for 15 new HDD bores. This includes instrumenting the pilot rods, and reamers. The instrumentation allows the project team to monitor rate of penetration, pump rates, tool torque, and downhole pressures during all aspects of drilling, including pilot hole development, reaming, and duct bundle pullback. Data collected is provided in real-time to all team members using wireless links for immediate evaluation. The instrumentation, coupled with a site-specific drill fluid design, has allowed immediate response to elevated annular pressures, significantly reducing the incidence rate of fracouts. The data collected also allows evaluation of the contractor’s activities, from the standpoint of drilling efficiency. This paper provides a summary of the HDD installations, the instrumentation used, and the benefits and lessons-learned from real-time downhole data acquisition.