Development options for Norwegian prospects
- Regional cross-section through the Helland-Hansen Arch showing the location and objective of Norske Shell's current well, 6505/10-1 [90,366 bytes].
- The Ormen Lange structure extends more than 80 km north to south, and lies in water depths of 500-1,200 metres east to west [10,958 bytes].
At the instigation of the Norwegian oil ministry, the operators of deepwater licences have joined forces in the Norwegian Deepwater Programme to tackle common problems arising in the course of their activities and identify cost-saving measures.
After undergoing a NKr 43 million upgrade, Diamond Offshore semisubmersible Ocean Alliance started work on a series of deepwater wells in April 1997. So far, it has completed three, for BP Norge, Norsk Hydro and Statoil, and in late March it was about to spud a fourth, for Norske Shell. Later this year semis Transocean Leader and Scarabeo V are due to join the campaign. Next year, the West Navion I drillship is expected to participate.
Drilling to dateOf the three wells drilled so far, only Statoil's Vema Dome well, 6706/11-1, was a disappointment. However, both BP and Hydro made large gas finds, thus justifying the enthusiasm shown for the acreage in the run-up to the licence awards.
The most sought-after acreage was the Nyk High licence PL 218, covering block 6707/10 and part of 6706/12 on the Voering plateau. According to industry opinion, the acreage contains a potential one billion BOE. But in common with the other licensed deepwater areas, the probability of gas is rated much higher than that of oil.
The well, 6707/10-1, was drilled in a water depth of 1,274 meters, almost three times as deep as any previous well on the Norwegian continental shelf, according to Per Svela, BP's partner liaison manager. The well was located 50 km from the nearest existing well. Drilling was directed at the Luva prospect, and found gas in Upper Cretaceous sandstone at depths of 3,000-3,725 meters. Reserves are provisionally estimated at 1.5-2 tcf.
The sands are very clean and have very good porosity - possibly among the best yet found in North-West Europe, according to Svela.
A flat spot identified on the seismic data turned out to be located at the bottom of the gas column, as expected, but the liquid underlying the gas was water. However, there were traces of oil in the water, raising the question of where the oil has migrated. BP plans to drill a second well on Nyk High in late 1998 or early 1999.
Statoil's Vema Dome well, 6706/11-1, was located some 20 km to the west of BP's, and drilled in 1,238 meters water depth. It also penetrated a good sandstone reservoir in the Upper Cretaceous, but found only slight gas shows.
Norsk Hydro's well was drilled on the massive Ormen Lange structure further south in the Moere basin. Its license, PL 209, covers blocks 6305/1, 2, 4 and 5; the southern part of the structure extends into 6305/7, which forms part of BP's PL 208 licence. Gas, mainly methane, was found in good quality sandstone in Early Tertiary horizons. Reserves proved by the well are put at 3.5 tcf, but together with probable reserves, could be as high as 12.7 tcf.
There are signs that there could be a thin oil leg below the gas, and this possibility will be tested by a well which BP plans to drill in the south of the structure this summer. Hydro itself is planning a second well in the north later this year.
In late March, Shell had planned to spud an exploration well 6505/10-1 in 684 meters water depth in the Voering Basin. It was to be drilled on Helland-Hansen, a major structure with three structural highs, according to Tony Evans, deepwater exploration team leader.
The objectives are in the Upper Cretaceous, with a primary target at around 3,200 meters and a secondary one at 3,750 meters. The three-month well is high-risk, with only a 10% chance of success, and gas thought more likely than oil. If successful, however, the rewards could be great, with possible reserves of 4-20 tcf.
Production schemesShell, which is involved in deepwater developments in the Gulf of Mexico, has already sketched out some initial development scenarios. If oil were found, it could be produced to a tension-leg platform tied back to a production ship for processing and stored in a floating storage vessel. In the case of large oil reserves, two TLPs could be called for, and gas injection used to assist recovery.
A gas/condensate scenario could involve subsea wells tied back to a Draugen-type platform, with storage for the liquids, in waters of around 250 meters. Another possibility, for both oil and gas/condensate, is a spar platform.
In the case of Hydro's Ormen Lange, seabed topography and the occurrence of earthquakes pose a major development challenge, for the field, which extends 80-90 km north to south, lies beneath a steeply shelving seabed in water depths of 500-1,200 meters.
Current thinking at Hydro favors the use of single subsea wells tied back to manifolds, with production being exported back up the shelf to a process platform in waters of around 300 meters. These pipelines could float some 20-40 meters above the seabed to avoid the risks presented by earthquakes and shifting seabed material.
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