Pressure, patience and persistenceCNOOC’s Bas Spaargaren spoke at the Propex 2019 conference in London. Photo: Ingvild Carstens

Pressure, patience and persistence

The road to discovery of the 250 mmboe Glengorm gas field in the North Sea has been long for CNOOC and its partners.

– The three P’s; pressure, patience and persistence, these are the key elements behind the successful discovery of Glengorm, said Bas Spaargaren, Vice President Exploration & Appraisal, Europe & Africa at CNOOC International during his talk at the Prospex 2019 conference in London on December 11th.

The discovery of the 250 mmboe gas and condensate field in the North Sea was first announced in January this year. CNOOC is the operator (50 % interest), while partners Total and Edison each hold a 25 % interest.

According to Spaargaren, the prospect had existed for years, and other oil companies had previously held and given up on it. Then, CNOOC wanted to give it a try. A lot of 3D seismic data were acquired, and some failed drilling attempts followed. However, the company did not give up, and in the end, their persistence and patience paid off.

The field is the largest discovery in the central North Sea in over a decade, and the largest on the UK shelf since the Culzean gas field was discovered eleven years ago.

Glengorm is situated in a high-pressure area, which represented a challenge before and during drilling. The pre-drill prognosis was however almost identical to the actual result, a feat CNOOC, of course, was very pleased with.

Location of the Glengorm discovery in the Central Graben. Figure: Total

Seal a key risk

The acreage around Glengorm was previously held by Maersk Oil, and at one point released due to failure to de-risk the top seal integrity of the HPHT Upper Jurassic prospects in the area.

CNOOC and the partners also considered the seal – the containment – to be the main risk of the prospect. They were already aware of the presence of blown/leaky traps in other exploration wells in the area.

The key breakthrough on the road to discovery, according to Spaargaren, was the recognition of the protected trap.

The discovery could de-risk other Jurassic prospects with similar traps and depths/pressures in the area.

Glengorm is located in licence P2215 at a water depth of approx. 86 meters. The exploration well was drilled to a total depth of 5 065 meters and encountered net gas and condensate pay zones with a total thickness of 37.5 meters.

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