Coastal shoreline crossing using horizontal directional drilling for pipeline installation achieves excellent environmental and social outcomes

As part of the Devil Creek Development Project, Apache successfully used horizontal directional drilling (HDD) with a delayed break out as the installation method for the shoreline crossing of a new gas pipeline at Gnoorea Point, 45 km southwest of Dampier, Western Australia to achieve excellent environmental and social outcomes. Technical, environmental and community engagement challenges included an HDD reach distance of 1.85 km, a delayed break out technique, hard complex and variable geological strata, the HDD exit point in shallow water (6 m) and surrounded by benthic habitats consisting of corals, seagrass and macroalgae within a Marine Conservation Reserve, stringent regulatory requirements and the onshore drilling location directly adjacent to a heavily used camping area and a public boat ramp with adjacent beach. Application: To achieve minimal disturbance to the marine environment and social amenity of the surroundings, an extensive and innovative marine monitoring programme was used in combination with an intensive community engagement programme. The techniques used for this project have application to oil and gas activities involving stringent regulatory requirements, sensitive marine environments and proximity to public amenities. Results, Observations and Conclusions: Mapping of the drilling fluid showed a small area of the seabed that was affected. Some small, unplanned areas of leakage of drilling fluid onto the seabed were also identified and the leaks remediated: these leakages occupied only a very small area of the seabed. Apache were required to demonstrate that HDD activities resulted in no more than 0.5% loss of seagrass, macroalgae and coral based upon losses predicted from mapping, modeling suspended sediment concentrations in the water column and sedimentation rates on the seabed based on drilling fluid discharge rates and applying conservative coral health threshold criteria to discharge model outputs to predict zones of impact to benthic habitats. An extensive marine monitoring programme, sampling before and after HDD, using high definition video camera to capture photoquadrats conclusively demonstrated that losses were significantly less than predicted and permitted. Drilling operations were a 24 hour activity and located directly adjacent to a popular camp site and boat ramp. Apache engaged with the community before and during the HDD activity and no complaints were received from the users of the area during operations. Significance of the Subject Matter: Provides an example of industry's ability to operate successfully in sensitive marine environments and close proximity to communities.