Completing horizontal directional drill (HDD) projects in areas congested with other utilities comes with unique difficulties which can be exacerbated when the congested area is a pipeline corridor such as the ExxonMobil Nederland to Beaumont pipeline corridor.
In order to successfully complete projects in these crowded areas, engineers and HDD contractors must be thorough during the planning and construction phases of a project.
ExxonMobil commissioned the design and installation of seven pipelines between various facilities along the corridor. ExxonMobil partnered with UniversalPegasus International (UPI) to contract and manage the design and installation of the pipeline project. UPI contracted GeoEngineers (GEI) to perform the engineering and design of the trenchless pipeline installations and Troy Construction (Troy) was selected to complete the construction scope of the project. Troy subcontracted Laney Group Inc. (Laney) to perform 15 trenchless installations utilizing the HDD construction method.
The 15 HDD installations ranged between 886 ft and 5,400 ft in length. The installed product pipes were installed either as single pipe or as bungles in various configurations and ranged between 6 in. and 24 in. in diameter. The single 10-in. diameter HDD installation had a final reamed hole size of 18 in. while the largest bundle required a final reamed hole diameter of 48 in. Several of the HDD installations were complex and included multiple horizontal curves, limited workspace areas and working in the highly congested pipeline corridors.
HDD Engineering in a Pipeline Corridor
GEI completed the early design phases and Integrated Trenchless Engineering (ITE) completed HDD designs to adjust for field conflicts prior to construction. HDD design, whether part of the design phase or during the preconstruction phase, plays an integral role in the success of any HDD; however, for HDD installations in congested areas like the pipeline corridor it is even more important. First, accurate as-built data for all pipelines in the area are necessary in order to establish the appropriate locations for the entry and exit points, as well as the profile of the HDD. In addition, the entry and exit workspaces must be able to accommodate entry and exit pit excavations and the placement of heavy construction equipment.
Deadman anchors had to be driven to provide lateral load capacity at the rig during drilling and pullback operations and existing utilities in the workspaces had to be avoided. In addition, the depths of the existing utilities were compared to the HDD geometry in order to avoid potential conflicts. Finally, ExxonMobil drill tolerances were taken into consideration during the design phase, so the HDD contractor had sufficient space to make any adjustments necessary to complete the HDD successfully and avoid existing utilities.
HDD Operations in a Pipeline Corridor
The operations team took great care during the preconstruction phase to reduce the risks during construction phase. The primary risks the Laney Drilling Team mitigated were working in and around the numerous pipelines in the corridor and accurately steering during pilot hole operations to avoid potential contact with existing utilities.
Load dispersing materials and timber mats were placed to protect the integrity of existing pipelines that were to remain active during construction. The primary considerations for equipment placement were the equipment weight and the potential for ground disturbances required to operate a piece of equipment safely. Placement of heavier equipment like the drill rig and the drilling fluid cleaning system directly over shallow pipelines was avoided where possible. Additional caution was taken for the placement of the drill rig to provide space for the deadman anchors and the excavation of the fluid containment pit.
As construction began, the pilot hole was the highest risk part of the construction phase because of the potential of intersecting an existing pipeline. The secondary survey system used while steering the pilot hole was critical in helping the HDD surveyor evaluate the position of the drill bit in relation to the existing utilities. The surface wire used in the system induces a magnetic field which the downhole sensor uses to locate its subsurface location. This magnetic field is disrupted when near other pipelines and the sensor interprets the interference as a potential contact risk.
There are extensive risks to performing pipeline installations utilizing the HDD construction method in congested pipeline corridors. These risks can be mitigated during all phases of the project from design to construction by careful planning and execution. The HDD design phase requires detailed information gathering and HDD designs that consider the locations of the existing utilities, so the HDD installations are constructible. In addition, detailed planning by the construction team is important to mitigate the risks of working in and navigating around an active pipeline corridor.
Because of high-quality HDD designs by GEI and ITE and proper planning and execution, Laney successfully completed all 15 HDD installations between June and December 2019. Laney and ITE take an integrated construction and engineering approach to all aspects of any trenchless project to reduce risk and provide exceptional engineering and construction services.
D. Cole Byington, E.I.T. is project engineer and Andrew Sparks, P.E., is director of engineering at Integrated Trenchless Engineering Inc. Larry Hereford is project manager at Laney Group Inc.