The Oseberg field centre in the North Sea (Photo: Vegar Stokset)
"The first results are promising, but we need to test further before we can evaluate the potential," says Morten Mikkelsen who heads petroleum technology in the Oseberg organisation.
Since Oseberg began production on 1 December 1988, the Shetland Chalk formation has been just one of the structures the drill bit has passed on its way down to the Brent sandstone formations.
StatoilHydro has long been aware that oil and gas also lie in the upper part of the field, but the production characteristics in the tight chalk are much more difficult than in the main reservoir. This part of Oseberg has therefore remained untested until now.
The goal is to see if commercial production is viable with well B-24 B, which is now in production. Thanks to jointing having been carried out, production in the start-up phase is good, but it will take time to gauge the well's long-term productivity.
10 production zones
Drilling operations began on 17 April. After the well's completion, it was first perforated with the aid of explosive charges at intervals of roughly one metre.
Hydrochloric acid is then pumped into each of the well's 10 production zones.
The acid has reacted with the chalk and formed fissures that can stretch more than 50 metres from the drilling hole and thereby increased productivity.
"We began acid treatment in the well on 15 October and have since carried out a selective treatment of all 10 production zones," says Sigurd Erlandsen, who heads the B-24 B well project.
"The well start-up confirms that production characteristics have improved significantly using acid treatment."
Interesting potential
StatoilHydro's specialist communities within petroleum technology, well intervention and drilling have been key to operation planning and implementation.
For the company's contract team it has been a challenge putting the acid stimulation into practice, since chemical vessel access in the market is tight. StatoilHydro has therefore developed a solution where pumps and tanks have been welded on a supply vessel.
"It's been an incredibly exciting project implementation, and the specialist communities involved deserve credit," says Mr Erlandsen.
In the best case, this could be the start of a drilling campaign stretching over many years. The Shetland Chalk formations will then be greatly
upgraded, from a transport stage to a fully-fledged oil producing zone that increases the operational and commercial lifetime of the Oseberg field.
Facts:
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