Abstract
Pembina Pipeline Corporation and SemCAMS Midstream, as two independent companies, both have development projects near Grande Prairie, Alberta. A large component of both projects required pipelines to be installed across the Wapiti River. BlueFox Engineering was retained on behalf of the two owner parties to work on three parallel crossings using the HDD intersect method, in order to install six (6) pipelines. A collaborative agreement was achieved between various parties to share resources and information, including subsurface investigation information, the HDD contractor, HDD entry and exit workspaces, pipeline layout space, lessons learned from each crossing, support services and access maintenance. The successful collaboration resulted in a significant reduction in cost, time and environmental footprint.
Introduction
As part of the multi-phase expansion program by Pembina Pipeline Corporation, several project upgrades, new pump stations, civil works, and pipelines were proposed for 2019 construction in northwestern Alberta, near Grande Prairie.
A significant component of these projects was the construction of the La Glace to Wapiti pipeline expansion, which required two parallel HDD installations for NPS 16 (406.4mm) and NPS 12 (323.9mm) pipelines across the Wapiti River. Both new pipelines would transport high vapor pressure (HVP) products in order to expand the company’s capacity in this region.
Simultaneously, SemCAMS Midstream also proposed the construction and operation of a central facility and associated pipelines to support the ongoing development of the Montney liquids rich natural gas formation. The proposed Central Facility will include gas processing capability up to 280 million cubic feet per day of sour gas and 20,000 barrels of condensate and other natural gas liquids. In addition to the plant, up to six pipelines will be constructed in a common right-of-way leading south of the plant. These pipelines would transport sweet natural gas, sweet natural gas liquids, produced water and waste gases to existing infrastructure in the area.
Similarly, a significant component of this company’s project also required crossing the Wapiti River. As such, four pipelines, 3x NPS 8 (219.1mm) 1x NPS 4 (114.3mm) were designed by BlueFox Engineering in a bundle crossing beneath the Wapiti River to transport sour gas, liquids and fuel gas, within an adjacent right-of-way to the NPS 12 and NPS 16 right-of-way for Pembina’s HVP transportation pipelines.
The proposed Wapiti River crossings are located roughly 25km southwest of Grande Prairie, Alberta, with the subject section of the Wapiti River flowing primarily east to west, just before the river turns south immediately to the west of the proposed crossing alignments. The route for the 3 adjacent HDD crossings were selected to align roughly perpendicular to the watercourse, adjacent to an existing overhead powerline river crossing.
The Wapiti River is situated at the base of a ravine that is approximately 130m deep and 800m wide from crest to crest at this location. The north slope is steeply inclined at approximately 1:1, whereas the south slope is more gradual with a general inclination of 2:1.
BlueFox Engineering was retained on behalf of the midstream owner companies to provide HDD engineering, detailed design, construction planning and tendering, environmental monitoring, UAV thermal imaging, mud management and construction inspection services in order to complete the crossings. As part of our scope of work, a significant component was dedicated to feasibility and risk assessment, as well as management of construction resources and collaboration between two independent owner parties completing parallel crossings sequentially, while not disturbing adjacent construction activity.
GeoTechnical Investigation
Given the Wapiti River valley size and ravine depth, an extensive geotechnical program was undertaken, totaling five deep (up to 130m) geotechnical boreholes and one geophysical electrical resistivity tomography scan. Subsurface information gathered was agreed to be shared with both owner firms completing the crossings.
Subsurface investigations encountered varying stiffness high plasticity clays with occasional gravel and cobbles, overlying sand with silt or clay till above bedrock. The bedrock primarily consisted of interlayered sandstone, siltstone and claystone with significant variability in compressive strength and identified poor quality bedrock zones of intense fracturing and coal seams.
As part of the subsurface investigations, a slope stability analysis was performed which identified signs of bank erosion and debris avalanches along the northern bank of the Wapiti River which was identified as an area of high risk for landslide initiation.
Based on subsurface investigations, slope stability requirements and pipeline stress criteria, BlueFox Engineering elected to design the HDD crossings with significant setback from top of banks and considerable depth of cover to mitigate the identified risks of impact to the pipeline. Entry and exit points and HDD work pads were selected based on the HDD geometry, equipment sizing specifications, sufficient water storage and collaboration for sharing support resources between both parties.
HDD Design
Final detailed HDD designs included 30m surface casing to be installed at both entry and exit points of each crossing in order to mitigate the effects of the surficial clays, cobbles and gravel and to mitigate the effects of hole ovalization near surface due to the long duration anticipated of the project. Casing diameters were specified to be NPS 48 (1219mm), NPS 36 (914mm) and NPS 30 (762mm) respectively, based on the final borehole reaming diameters of each crossing, which were 30” (762mm), 24” (610mm) and 18” (457mm).
Entry and exit angles for each of the drills ranged between 13 degrees and 18 degrees in order to balance pipeline lifting height requirements with the amount of surface casing required. In collaboration with both midstream companies, BlueFox Engineering designed the 3 parallel HDD crossings within two right-of-ways in order to provide vertical and horizontal offsets to meet specifications, allow for adequate steering tolerances, minimize the risk of drilling fluid communication between boreholes, and to facilitate HDD equipment setup and configuration requirements on surface while allowing tie-in and pipeline completion activities on the adjacent drills.
The 3 parallel drills were each designed to be executed using the HDD intersect method, Figure 1. This was selected due to surface casing installation on both entry and exit points, the overall duration of the project and length of the crossings, which totaled 1781m, 1862m and 1856m, respectively. The pilot intersect location was designed with relative consistency for all three drills, with the entry side rig drilling approximately 2/3 of the pilot hole and the exit rig completing the intersection near bottom of the inclination tangent near the exit side. The resulting HDD geometry experienced over 240m of elevation change and consisted of 7-segment drill paths for all three crossings; entry tangent, entry arc, bottom tangent, exit side inclination tangent, declination arc and exit tangent.
The maximum allowable annular pressure was calculated using modified Delft equation.
By combining hydrostatic pressure induced by the weight of the drilling fluid and the frictional pressure calculated based on Bingham Plastic Model we determined the circulating pressure. This circulating pressure was designed to be maintained lower than the maximum allowable annular pressure in order to reduce the risk of hydrofracture and inadvertent drilling fluid release to the ground surface.
In Figure 2 to 4, the circulating pressure was calculated from both entry and exit points due to the intersect construction method and this value was increased by 20% (the circulating pressure + 20%) to take account for uncertainty during construction for material notfully cleaned from the borehole.
Overburden pressure was calculated based on the assumed soil unit weight and measured ground profile as a reference. It is noted that the circulating pressure + 20% is always below the limitation (maximum allowable annular pressure obtained by Delft SF method), except for a short distance near the entry and exit points. However, due to the installation of surface casing at the entry and exit points, the risk of hydrofracture in these two regions is reduced. This held true during the construction phase that no inadvertent drilling fluid releases to surface occurred.
Collaboration and Shared Resources
As part of the planning and collaborative approach between all parties, the HDD entry and exit workspaces, as well as, the near 2,000m pipeline drag section layout space was able to be shared in a common temporary workspace, significantly reducing required tree clearing, the environmental impact, costs, schedule and resources required.
Due to a late winter start and the overall duration of the project, access to the HDD locations became increasingly difficult and significant on-going maintenance was required. Early engagement with multiple parties during the project planning phase allowed for shared resource agreements to be established, reducing project costs as several support services and access maintenance was able to be shared throughout the construction life cycle.
A mud management program was developed by BlueFox Engineering during the detailed design engineering phase, which illustrated the drilling fluid program required for each HDD borehole, along with water consumption and drilling mud disposal requirements. Several water sources and disposal locations were scouted by BlueFox pre-construction, and upon completion of the first and second HDD boreholes, the remainder of nearby water sources and disposal locations were shared by SemCAMS and Pembina for the rest of the HDD program, which significantly reduced travel times and upheld positive relationships with landowners in the region.
Construction
Construction of the 3 parallel crossings was awarded to Direct Horizontal Drilling, to be executed with two equivalent HDD rigs, Table 1.
Construction on the first drill commenced on February 10, 2019 with the 4-pipe pipeline bundle successfully pulled on April 16, 2019 and the HDD rig demobilized over to the second right-of-way on April 18, 2019.
Several successes and lessons learned on the first HDD were discussed between BlueFox Engineering and Direct Horizontal Drilling, including a thorough bedrock mapping and loss of circulation zones which identified and correlated to the measured depth elevation on the upcoming drills. In addition, an adjustment to the reamer tooling assembly was made based on feedback throughout the alternating bedrock formation and corresponding rates of penetration encountered on the first drill.
Construction for the NPS 16 drill commenced on April 19, 2019 with the pipeline pull successfully completed on May 27, 2019 and construction on the NPS 12 line starting immediately thereafter. Again, with lessons learned on the successful passage through this location for the NPS 16 pipeline, BlueFox Engineering and Direct Horizontal Drilling proposed to forward ream to the final 18” diameter on the exit tangent to 600m while waiting for the entry side HDD rig to complete it’s journey of 1,200m during the pilot hole stage. The decision was approved by the Pembina project team and the final NPS 12 pipeline was successfully installed on June 26, 2019, approximately 30% ahead of schedule. Figure 5 shows the planned and actual days of all 3 crossings.
Throughout the project, full time in-stream water quality monitoring and unmanned-aerial-vehicle (UAV’s) monitoring for inadvertent fluid release to surface was utilized as part of the environmental monitoring program. In combination with scheduled terrestrial walks, the day shift UAV pilot would perform UAV flights in areas difficult to access by foot and across the watercourse from both entry and exit side. Day time interpretation was based on RGB color photo and video data and visual interpretation, Figure 6. Night shift UAV flights were conducted using a larger vehicle, fitted with a thermal imaging camera, Figure 7. Corresponding photo, temperature and video data was interpreted by the UAV pilot to detect surface fluid release. Baseline readings of drilling fluid, ambient air and ground surface were taken several times per day in order to calibrate equipment. If anomalies were detected by a UAV, additional investigation on surface was conducted by terrestrial monitoring personnel. On average, the drilling fluid temperature was recorded at 30 Degrees Celsius by downhole sensors, contrasted by average ground surface temperatures below 10 Degrees Celsius.
Although drilling fluid circulation was intermittently lost, it was subsequently regained throughout each of the 3 crossings through implementation of various drilling techniques and addition of intermittent drilling mud additives in select zones. No drilling fluid to surface or within the water course was detected by UAV, terrestrial environmental monitors or in-stream sonde monitors, Figure 8. attributing to the success of the installations.
Conclusion
In total, 10,842m of pipelines were installed within the 3 parallel boreholes, 35m apart, over the course of 4 months without any lost time incidents, significantly reduced surface disruption due to the collaborative efforts of the projects, and without any environmental impact to the watercourse or fluid release to surface.
This was achieved utilizing various shared resources between the two owner companies, continuous 24 hour per day drilling utilizing the HDD intersect method, a thorough understanding of site specific and subsurface conditions, various detailed engineering and execution plans, on-going lessons learned, swift response to changing drilling conditions, and a robust team of support contractors, consultants and specialists working towards a common goal.
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