The Project involved the construction of potable water pipelines and sewer pressure mains between Queensland’s Gladstone mainland and Curtis Island, to facilitate the provision of utility services to meet demand growth associated with liquid natural gas facilities in the area.
The project featured a number of technical milestones for Trenchless Technology in Australia, with Coe Drilling and Mears Group Inc delivering the first use of horizontal directional drill (HDD) intersect technology in Australia on all three harbour crossings. It also encompassed the first use of gyroscopic steering tools on hard rock crossings involving HDD intersects, and also the deepest recorded high density polyethylene (HDPE) marine crossings installed at depths of over 75 m.
Design and engineering
The use of HDD was the logical choice for crossing Gladstone Harbour. However, detailed project engineering and design was required to confirm that the proposed methodology could achieve a successful installation of the product pipelines.
The initial review during the risk analysis and procedure development revealed that a conventional HDD crossing would create excessive down-hole pressure on the formation leading to a potential frac-out beneath the harbour.
Conventional HDD would have proven difficult to guide and maintain directional control. Given the risks and sensitivity of the works within Gladstone Harbour, the HDD intersect used the Gyro Steering Tool Procedure developed with Mears.
Product pipe selection and installation at depths in excess of 75 m had to be designed and engineered for the project. Mears had completed several HDD intersect projects in the US, and also had previous experience in the use of the Gyro Steering Tool.
Work commenced with mobilisation of two 500 tonne drilling spreads from the Coe yard at the Gold Coast; to the Gladstone mainland and on Curtis Island.
The detailed engineering analysis proposed to install steel enveloper pipelines within the boreholes first, and then install the PN 25 HDPE product pipelines within the steel enveloper pipelines.
Drilling operations commenced in early November 2011 using an American Augers DD1080 drilling spread. With the presence of loose overburden gravels and cobbles material, steel conductor casings were required to be installed for up to a 120 m borehole depth. In total 20 inch and 36 inch steel casings were installed, using a wash-over technique on the smaller 20 inch casings and applying a GrundoRam Tauras Pneumatic Hammer, which has a dynamic loading in excess of 2,000 tonnes on the larger 36 inch casing.
The Pilot holes were drilled using 12.25 inch TCI Bits driven by 8 inch mud motors using both conventional magnetic guidance systems to set the entry steel conductor casings and followed by the gyro steering tool to provide guidance beneath the busy Gladstone Harbour.
Drilling operations took place from the mainland and Curtis Island followed by the use of Rotating Magnets to complete the first intersect on 20 December 2011. Hole opening was achieved using split bit hole openers to a maximum of 32 inch diameter on the largest of the boreholes.
As part of the procedure, the steering tools were equipped with ‘pressure while drilling modules’, which allowed the pilot hole annulas and internal pipe pressure to be continuously monitored to limit any potential drilling fluid releases and environmental damage.
On completion of the hole opening operations, the first of the prepared steel enveloper pipelines were installed. The steel casings were then flooded with water prior to installation of the HDPE 100 PN 25 Product Pipelines, to minimise stresses in the pipeline during installation.
At one stage in the operations a third 100 tonne HDD rig was mobilised and put to use to install drill string within the steel casing and install the DN 250 HDPE Pipeline, while the HDD drilling and intersect works took place in the adjacent borehole less than 8 m offset.
The project was situated close to the Great Barrier Reef Marine Park border. Such environmental significance was integral to the choice of the drilling methodology. The preferred option as adopted in the referral of proposed action document was an HDD crossing.
However, it was the utilisation of HDD intersect technology – drilling from both sides to meet in the middle – that ensured the success of the project with no environmental harm caused to the Harbour during the completion of the HDD works.
Safety – zero harm
Specific programs were developed to address both customer and Coe’s objectives through adherence to a strong safety and health policy that exceeds industry standards.
One innovation was the implementation of MYOSH on the project. MYOSH is a remote and real time occupational, safety and health system computer compliance management system.
Utilising the capacity of this system meant that hazards and risks could be identified early, and mitigation measures implemented in real-time to limit exposure of potential risks and hazards to the workforce.
The job was completed in April 2013. Following on from the recent success of the first HDD intersects in Australia and the use of the Gyro Steering Tools, Coe has received several enquiries on the benefits and is confident that the technology will lead to further advances for the HDD industry in Australia.