Energyworks used a combination of innovative pipe-laying and remediation techniques to minimise the environmental impact of two major oil and gas pipeline projects the company completed in Taranaki last year.

The New Plymouth-based company used a combination of heli-stringing and horizontal drilling to reduce the impact of Contact Energy’s 8.5 kilometre Ahuroa gas pipeline and multiple export and gathering pipelines it laid for Todd Energy over about 9 kilometres branching out from the company’s McKee-Mangahewa production station.

Using helicopters to deliver pipeline sections to the site reduces truck and excavator damage alongside pipeline routes and eliminates the excavations sometimes required for access roads. As well as reducing traffic in sensitive environments, the use of helicopters also reduces overall fuel use and emissions.

Energyworks employed about 2.4 kilometres of horizontal directional drilling across the two projects. While the technique has mainly been used to install pipe under rivers, roads, or other barriers, the company also advocates its use as an environmentally preferable alternative to trenching. It was recently contracted by Vector to use HDD for the majority of a seven-kilometre pipeline connection for the Yashili dairy plant in Pokeno.

Where horizontal drilling wasn’t an option, as was the case at two significant river crossings for the Ahuroa project, Energyworks came up with a suite of techniques to minimise downstream pollution and damage around the crossings.

A pump/flume system was created to ensure clean upstream water could pass around the `dry’ riverbed worksite and continue downstream.

During excavation, all the removed material was placed above the flood level and contoured to avoid erosion. Silty material was removed and rock introduced to help stabilise the riverbed.

The process also reflects Energyworks’ recognition of the importance of asset longevity. Pre-welded sections were encapsulated in protective concrete sleeves to eliminate the risk of rock damage to the pipe over time and avoid the need for any future disturbance of the riverbed for repairs.

Similar techniques were used on a large number of smaller river crossings involved in the Mangahewa project. One area, where a stream ran along the base of a steep papa bank, was particularly challenging.

Drilling was impractical given the steepness of the bank, so the company engineered a tailored reinstatement plan to ensure the bank would hold long term.

Drainage was added once the trench was excavated and the pipe installed. Bags of sand and cement were used in combination with geogrid to form terraces and drainlines were installed at the rear of each terrace. Biomac blanket was then pinned to the geogrid and covered in topsoil, creating a microclimate for seed germination. The area was then hydro-seeded to ensure a successful grass take given the site’s southerly aspect and the time of the year.

For its efforts on the two projects, Energyworks was declared a winner in the business category of Taranaki Regional Council’s 2013 environmental awards.

The Environmental Excellence award category is sponsored by PEPANZ