Telfer Gas Pipeline Project
Ancon
Directional Drilling (ADD), a leading Australian Horizontal Directional
Drilling (HDD) company, has been awarded HDD works on 11 River, Road and
Rail crossings as part of the Telfer Gas Pipeline Project in Western Australia.
The crossings were awarded to Ancon by McConnell Dowell, an Australian
based multi-discipline engineering and construction company. The Telfer
Gas Pipeline, upon completion, will be 442km long and provide gas to the
power station at the mine site. The pipeline will run in a continuous
length from Port Hedland to the Telfer Gold-Copper Mine.
The Regional Environment
Port Hedland has a population of almost 13,000 and is situated in the
Pilbara region, 1,600 kilometres north of Perth and 650 kilometres south
of Broome. With the Great Sandy Desert nearby, the tropical, semi-desert
climate is one of Australia's hottest, with temperatures ranging from
0 - 50° C. Port Hedland is the major port of the Northwest and, overlooking
the Indian Ocean, is home to an expanding Iron ore industry consisting
of some of the world's biggest mines. The region also caters to another
major industry, Salt production, with 2 million tonnes exported per annum.
The Pilbara region contains Banded Iron Formations that are more that 600 million years old and consist of Pisolithic Ironstone deposits, Hematite Iron Ore and Quartz. With Quartz having a hardness rating of 7 and Iron being magnetic and around 8 times heavier than water (its relative density is 7.87), the area provides for challenging HDD conditions.
Project Considerations and Solutions
Two of Ancon's primary river crossings are of substantial length with
De Grey River crossing at 704 metres and the Strelly River bore at 467
metres. The installation of the 250 mm gas pipeline will be completed
using the Ancon's Gallagher HDD 400 drill rig, and Ancon 1000gpm mud system,
both of which were built to Ancon's specifications. The Ancon drill rig
has the following capabilities:
• Power Unit: 605 Horse Power Electronic Cummins turbo diesel engine
• Rotary drive:82,000 Ft lbs @ 26rpm
• Max speed: 22,000 Ft lbs @ 82rpm
• Mud flow: up to 1,400 Gallons per minute
• Mud pressure: up to 5,000 PSI
• Carriage drive:185 tonnes
• Drill pipe: Range 2 up to 12" collars
• Total weight 40 tonnes
Environmental conditions are quite stark and tenuous so the utmost care must be taken to preserve them. Due to the desert conditions, there is limited water availability. One billabong on the Strelly River supplies the local animals, including cattle, and native wildlife with their water supply. Water for the use in the drilling process must be carted in by water tankers from nearby underground borefields. The De Grey River drill site however poses a different kind of situation. The residents are not necessarily all friendly and precautionary measures need to be taken to ensure that the large cantankerous female crocodile in local residence is avoided.
Strelly River Crossing (467 metres)
The bore profile has been planned with minimum pipe coverage of 5 metres
from the lowest point of each river, thus allowing for movement due of
riverbeds over time. The HDD drill site was established with an entry
point on the western side of the river. Using HDD technology allows the
single exit point to be an expansive distance away from the entry site.
This distance is dependant upon the rig being utilised. In this case,
the full 467 metres will be drilled in one length.
The steering probe is housed near the drill head and determines the path of the installation underground. The drill path is steered and monitored through the use of a magnetic guidance steering system. Coordinates of the bore path are taken and monitored at regular intervals by the Steerer and Drill Rig Operator, with reference to true magnetic north. These coordinates are translated into numerical data to present inclination and azimuth information for use by the surveyor.
The pilot holes are drilled using a 6 3/4" Mud Motor running an 8 3/4" Inch TCI Tri-cone and non magnetic drill collars. Drill fluid, consisting of American Petroleum Industry (API) grade bentonite, is injected into the pilot hole under pressure to facilitate erosion of the formation at a predetermined angle. Additives are used to condition the fluids to achieve the desirable properties that cannot be attained with water alone. The drilling fluid is continuously pumped through the assembly and 5 Inch API drill string throughout the pilot drilling process. This enables suspended particles to be carried out of the borehole for separation and recycling. Drilling fluid is filtered and recycled throughout the entire installation.
Upon full reaming of the bore path, a further "cleaning" pass is made to agitate any potentially settled or residual cuttings and dispenses any obtrusive materials in the tunnel wall. This will minimize the likelihood of abrasions to the installation pipeline coating.
Prior to placement into the bore, the gas pipeline is welded and tested, ready to be installed in a continuous length. The pipeline is pre-strung and the reaming assembly, with pipeline in tow, is retracted into the borehole from the exit site. Drilling fluids are continuously circulated from the jet nozzles located in the reamer, to support the annulus between the pipe and borehole wall, and to provide ample lubrication to minimise friction. This provides Ancon with a successful installation underneath the Strelly riverbed. Similar drilling processes are to be utilised at the De Grey River crossing.
Horizontal Directional Drilling (HDD) provides for a fast and accurate installation of key product without disturbance to the ground surface. HDD installation is an intelligent alternative for an ever-expanding, environmentally conscious culture. It provides installation with minimal disturbance to the ecosystem and local communities.
