Chevron unlocking shallow gas potential in Dutch North Sea
Jeremy Beckman, Editor, Europe
Chevron is taking gas production to the northernmost reaches of the Dutch North Sea. Its A12 project, due onstream by the end of the year, is also the first to harness shallow gas from a cluster of technically demanding discoveries dating to the early 1970s.
These fields extend in a crescent formation across five blocks in the Dutch A and B quadrants. There are no gas production centers in the area. The nearest is Wintershall’s A/6-B/4 in German waters 50 mi (80 km) to the north.
Chevron became operator of the blocks as a result of its merger with Unocal in August 2005. A year earlier, Unocal filed a development plan for the A12a field, shortly after acquiring the interests from the Shell/ExxonMobil joint venture, NAM.
Gerard Schut, general manager for Chevron Exploration and Production Netherlands, was at the helm of Unocal Netherlands when the transaction went through. He just had been re-assigned to The Hague after 10 years in Thailand. At that time, the company’s operated offshore production was modest, derived from five small, declining oilfields and two gasfields nearing depletion,
“Exiting from what we had was not a very lucrative option,” Schut says. “We did, however, see opportunities in numerous discoveries elsewhere on the Dutch shelf. When the A&B blocks came on the market in 2004, the gas price was still low. But we felt Unocal Netherlands had the organizational capability in place internally to develop this area, and to do so at relatively low cost.”
The package acquired from NAM comprised operated interests in two exploration licenses (B10a/A12b and B16a), and five production licenses (A12a, A12d, A18a, A18c, and B13a/B10c), which included five mid-size gas structures.
“The companies that drilled the discovery wells over the years had been targeting deeper horizons,” Schut explains, “and in each case ran into shallow gas, which is normal at subsurface depths of around 400 m (1,312 ft). But eventually, they figured out that these big pancake structures warranted targeting with drillstem tests.”
Despite the potential volumes, development was held back by a variety of technical concerns, notably low reservoir pressure (30-60 bar or 3-6 MPa) and unconsolidated sands. NAM’s most recent attempt was its Neptunus project in 2001, the aim being to cut costs on marginal developments in different parts of the Dutch shelf via look-alike production platforms. In A&B’s case, NAM examined a re-locatable version to produce the various fields in sequence, but the scheme was never executed.
Following a review of the A&B blocks well data and existing 2D seismic, Unocal Netherlands commissioned Gardline to acquire a new, high-resolution 2D shallow seismic survey over one of the larger structures, the A12a field in 2005. This spring, Gardline conducted another survey over the B13 and A18 fields. The data is being interpreted by Chevron geoscientists.
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Volume 67 Issue 8
August 2007
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