The Ichthys Project is expected to be the largest oil and gas development in Australia’s Northern Territory. It will produce around 10m tonnes of gas a year and 100,000 barrels of condensate a day.
Arup conducted geotechnical investigations to confirm the suitability of a site for offshore gas processing. The firm’s services included geotechnical site investigation, geological modelling, seismic assessment, foundation engineering for gas plant components and interpretive reporting.
Drilling in soft ground
Performing ground investigations in dense mangroves is typically avoided because site restraints can lead to the use of inadequate techniques which yield limited information. Safely performing ground investigations in soft soil without compromising sensitive ecosystems or the accuracy of information is also a challenge for engineers.
This project presented Arup with an opportunity to overcome these challenges using the innovative Mangrove Buggy – an environmentally sensitive mobile platform designed to operate on soft ground.
The Mangrove Buggy
Owned and operated by J&S Drilling, the Mangrove Buggy enabled Arup to gather quality information safely and cost-effectively whilst maintaining the environmental integrity of the site.
The low pressure the Buggy exerts on the ground allows it to operate in soft conditions with little disturbance to the soil, greatly reducing the threat of producing acid sulfate soils which pollute the environment.
The Buggy acted as an amphibious elevated platform supported by buoyant pontoons. This allowed drilling and cone penetration tests to be carried out safely and independent of the tides.
An onsite laboratory performed soil classification, testing and environmental field screening tests. Much of the testing ran alongside the field investigation, saving time and avoiding the need for a third party laboratory.
Approval by both Northern Territory Government and the Commonwealth Government is required for the Ichthys Project to proceed. After a public review period the final Environmental Impact Statement was submitted for consideration in April 2011.
INPEX, international oil and gas exploration and production company, is also working with the local indigenous population through the Larakia Development Corporation to increase the skill of the local workforce and create employment opportunities.
Quality and quantity data
During the investigation the Mangrove Buggy facilitated the drilling of 29 boreholes and 39 Cone Penetration Tests (CPTs) and two Dilatometer Tests (DMTs). The total length of the drilling performed was 323m of PQ size (85mm diameter) with a maximum drilling depth of 18m achieved.
Despite boreholes being terminated at 18m or less, the drilling rig mounted on the Mangrove Buggy was capable of drilling up to 30m in these ground conditions.
Effective data management
Arup introduced a sample management system to monitor the large number of samples. Barcodes were attached to all samples collected during the site investigation, giving them unique identification.
Sample barcodes were scanned and details of the sample entered into a database. The database stored information on the sample source, collection method and quality. Sample details were transferred from PDAs into a central database that could be viewed on site and remotely.
The database provided an interface through which samples could be selected for subsequent laboratory testing.