North American Oil & Gas Pipelines

JUN 2018

North American Oil & Gas Pipelines covers the news shaping the business of oil and gas pipeline construction and maintenance in North America, including pipeline installation methods, integrity management innovations and managerial strategies.

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Page 36 of 43 JUNE 2 018 | North American Oil & Gas Pipelines 37 crossing feature. For example, HDD methods require drilling fluids throughout the drilling and product pipe installation process. Managing and controlling drilling fluid flow within an HDD bore is critical to a successful crossing. If adequate depth of cover cannot be afforded due to site constraints or other factors, a potential exists for these fluids to impact the water resource through an inadvertent drilling fluid return. If this potential is deemed to be high for a critical waterbody feature and cannot be mitigated properly, then this method of construction may not be suitable for completion of the crossing as the risks could outweigh the benefit of the meth- od. Site-specific constraints can include site topography, di- rectional changes of the pipeline alignment close to the wa- terbody, inability to attain a proper depth of cover, inability to attain an appropriate setback distance between a trench- less entry/exit location and the critical feature, presence of piles and structures, proximity to existing wells, presence of deep buried river channels, and other related factors. Shoreline crossings present additional challenges for pipe- line or conduit installations that are not typical of land- to-land based installations (see p. 34-35). These challenges arise from the inability to readily access the exit side of the installation, elevation differences between entry and exit lo- cations, trenchless method specific risks (e.g., management and control of drilling fluids and annular pressures), work- ing in a marine environment, exiting the trenchless installa- tion through soil materials, developing an installation strat- egy that maximizes onshore construction activities, and other site-specific items. It is important for trenchless designers to manage the spe- cific risks and constraints while balancing the challenges as- sociated with each plausible trenchless method for a given waterbody crossing. If risks are not adequately identified and mitigated, increased construction costs and damage to repu- tation may occur. Once the geotechnical risks and crossing specific con- straints have been thoroughly identified, the most appropri- ate trenchless or non-trenchless construction method can be selected for the crossing. The design can then be tailored to the selected construction method with appropriate risk mitigation measures incorporated into site specific crossing details, designs, drawings and specifications. Overly optimistic trenchless designs and use of trenchless methods where they may not be appropriate will continue to attract scrutiny from regulators, legislators, and the public when failures arise. It is recommended that project owners, designers, consultants, contractors, agencies and regulators work collectively to evaluate risks and address design/con- structability challenges to provide optimum opportunities for project success. Reference: Duyvestyn, G., Perkins, J., Petta, C., and Foltz, T., 2016. "HDD Used to Conquer Ohio River Crossing in Downtown Urban Environment", Proceedings of North American No-Dig 2016 Conference, Paper MA-T2-03, North American Society for Trenchless Technology, Dallas, TX, USA, March 2016. Glenn Duyvestyn, Ph.D., P.E., P.Eng., is vice president of the pipelines unit at the engineering firm Mott MacDonald.

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