Modern plumbers

They are called “plumbers with technology” – there are more than 40,000 of them and they operate in over 100 countries around the world, including New Zealand. By Neil Ritchie.

Weatherford International is one of the industry’s largest oil and gas service and equipment companies,  and though small in a global context, the Kiwi branch continues to be involved in some leading-edge, if not world-first, technological applications.

One of the latest was about two years ago while the jack-up Ensco Rig 56 was drilling four horizontal production wells at the offshore Taranaki Tui Area oilfield for operator Australian Worldwide Exploration and its partners.

“Weatherford supplied the low torque downhole tools, which were developed right here in New Zealand, and they could not have completed the wells as well as they did without us,” recalls Geoff Murray, Weatherford’s NZ sales and marketing manager.

The company’s downhole tools and techniques have contributed to AWE being able to produce more oil, more quickly, for longer than expected.

Oil flows exceeded 35,000 barrels per day (bpd) for almost the entire first 12 months of production from July 2007, and are still above 25,000 bpd, compared with pre-production estimates of less than 15,000 bpd. Recovery factors have increased almost 80 percent to an estimated 50 million barrels of oil, with the field already producing over 21 million barrels of that.

Murray says another, more recent example of the use of Weatherford’s leading-edge technology is the jack-up Ensco Rig 107 drilling the wells for the US$600 million offshore Maari oil field development.

The rig drilled the top part of each of the five production wells, three water injection wells, plus a spare slot (for any future well) with casing, so saving field operator Austrian firm OMV and its partners time and money.

Conventional exploration and production work involves drilling without casing and installing the casing in stages as wells progress. But the Maari wells are being completed more quickly by using drilling with casing.

All subsurface drilling involves using large drillbits, with their steel teeth literally chomping through the earth.

The reach of each drillbit (they get smaller the deeper they go) is extended by adding lengths of steel drill pipe on to the drillbit. Once certain depths are reached, the drillbit is pulled out of the hole and steel casing is pushed in to support the hole drilled and to prevent it collapsing – drilling without casing.

Although drilling with casing is commonplace, the Maari project is the first time in world that such big casing (24-inch) was used and the first time the technique had been tried in New Zealand waters.

“The first hole was a textbook drill,” says Murray, “in every aspect we were ahead of the programme.”

The Ensco rig initially batch drilled the first three of five oil production wells to a subsurface depth of about 900 metres, before kicking off the so-called “horizontal” section of the first well where over 1500 metres was drilled, encountering clean, oil-bearing sandstones within the upper part of the primary target, the Moki reservoir formation.

The rig then started the next well, while the first well was hooked up to the wellhead platform production facilities, ready to start flowing oil to the nearby floating production, storage and offloading vessel Raroa by late February or early March.

Besides saving time and money, Murray says drilling with casing also cleans holes, of debris and drilling muds, better than conventional drilling does. It also almost totally eliminates the risk of hole collapses.