Longford Gas Conditioning Project – HDD Engineering and QC Inspection

Client: Esso Australia Resources

Services Provided: Engineering and HDD QC Inspection

Completion Date: September 2013

Project Scope of Work: 

Stockton Drilling Services were engaged to assist in the design and construction supervision of twelve HDD’s for the Longford Gas Conditioning Project in Sale Victoria.

The development of a new gas conditioning plant to the east of the existing Longford processing facility required control cables and high voltage cables to be rerouted in and around the existing live crude oil and gas plants. This would be the first time HDD would be used to pass below live processing facilities in Australia.

Stockton’s developed a strategy where the scope would be split into two distinct parts. The initial scope known as the Northern Alignment would be packaged as seven drills to install conduits from manhole to manhole. These would be 125mm HDPE ducts and range in length from 150m up to 270m. These works could then be undertaken by a small rig operator outside the main plant areas using the minimum required footprint.

The second scope known as the Southern Alignment would be conducted from within the plant boundary with a drilled length of just over 1000m. The alignment would pass beneath existing infrastructure for Gas Plants 1, 2 and 3 and the Crude Stabilisation Plant. In total sixteen conduits for HV and earth cables would need to be fabricated and installed.

A number of technical decisions were made by Stockton’s to optimise the number and size of bores required for the Southern Alignment. It was determined that a dedicated DN280 mud return line would be drilled first. This would remove the requirement for road tankers within the plant and allow guidance cables to be installed below ground for steering the remaining bores. Together these measures would significantly reduce the impact on normal plant operations. The mud return line would also be a spare should any subsequent conduit be damaged during installation. Consideration was then given to whether the bores should be cased or uncased.

After analysis it was determined that sixteen DN160 conduits should be installed uncased grouped in four bundles of four. The conduits would be progressively ballasted with water during installation to minimise installation loads to ensure the bundles remained in their crucial trefoil configuration.

Results and Client Benefit:

All twelve bores housing the twenty-four conduits were successfully installed without incident and with minimal disruption to Longford operations. Longford Gas Plant who had never previously employed HDD have since seen the benefits of trenchless operations and as a result Stockton supervisors were employed on site again to provide the construction oversight on two further drills for raw water and stormwater pipeline upgrades.

http://trenchless-australasia.com/news/hdd_goes_under_live_gas_facilities/082955