Design, Drilling, and Testing of a Deviated HTHP Exploration Well in the North Sea

1994 ◽  
Vol 9 (04) ◽  
pp. 244-248 ◽  
Author(s):  
K.P. Seymour ◽  
Robert MacAndrew
Keyword(s):  
North Sea ◽  
The North ◽  
The North Sea ◽  
Exploration Well

The Cormorant Field, Blocks 211/21a, 211/26a, UK North Sea

1991 ◽  
Vol 14 (1) ◽  
pp. 73-82 ◽  
Author(s):  
D. J. Taylor ◽  
J. P. A. Dietvorst
Keyword(s):  
North Sea ◽  
Shetland Islands ◽  
The North ◽  
Stock Tank ◽  
Delta System ◽  
The North Sea ◽  
Reservoir Porosity ◽  
The Uk ◽  
Exploration Well ◽  
Water Depths

AbstractThe Cormorant Oilfield is located approximately 150 km northeast of the Shetland Islands in Blocks 211/2la and 211/ 26a of the UK sector of the North Sea, in water depths of 500-550 ft. The field was discovered in 1972 by exploration well 211/ 26-1 and consists of four discrete accumulations spread along a major, north-south trending fault terrace. Hydrocarbons are produced from Middle Jurassic (Bajocian) sands of the Brent Group, which was deposited in a wave-dominated delta system. The reservoir has a typical gross thickness of 250-300 ft, locally increasing to 550 ft over faults active during sedimentation. Reservoir porosity varies from 16-28%, with average permeabilities ranging from tens of md to 1300md. The accumulation contains under-saturated 34-36° API oil which was initially overpressured by some 1000-1270 psi. The stock tank oil initially in place and ultimate recovery are estimated at 1568 MMBBL and 623 MMBBL, respectively, reflecting a recovery factor of 39%. The reserves are produced through crestally-located wells supported by down-dip water injectors, and exported via two fixed platforms and an underwater manifold centre. To date, 59 wells have been drilled and 324 MMBBL (52%) of the estimated reserves have been produced.

scholarly journals Pockmark formation and activity, U.K. block 15/25, North Sea

1994 ◽  
Vol 41 ◽  
pp. 34-49
Author(s):  
Alan Judd ◽  
David Long ◽  
Michael Sankey
Keyword(s):  
North Sea ◽  
North Atlantic ◽  
Petroleum Exploration ◽  
Gas Migration ◽  
The North ◽  
Pit Formation ◽  
The North Sea ◽  
Recent Sediments ◽  
Migration Pathways ◽  
Exploration Well

Digital seismic reflection (boomer) profiles of an active pockmark, in UK block 15/25, North Sea, reveal that the feature was formed prior to the deposition of the most recent sediments, probably by vigorous (or even catastrophic) gas escape. This release may have been triggered by the melting of ground ice when North Atlantic waters first entered the North Sea after the last glaciation, about 13,000 years ago. Possible sources of the gas are investigated by examining the composite log from a nearby petroleum exploration well; it is concluded that, although the gas may .originate from the Kimmeridge Clay, it probably comes from lignites of Tertiary age. Its migration towards the seabed is interrupted by local accumulations at several horizons, the shallowest of which (<80 m below seabed) is trapped beneath clayey sediments of the Coal Pit Formation. The topography of the base of this layer apparently controls the location of gas migration pathways to the seabed. As these lead to pockmarks which formed long ago, and as these pockmarks are still active today, it is probable that the migration pathways have remained throughout the intervening period. Gas accumulating beneath the Coal Pit Formation may migrate laterally to reach the pathways.

A Novel Approach to Drilling Through Challenging Formations With Complex Logging Bottomhole Assembly in an Exploration Well, North Sea

2021 ◽  
Author(s):  
Anders Kallhovd ◽  
Neil R Kelsall ◽  
Erik Haaland ◽  
Jon Haugestaul ◽  
Erik Akutsu ◽  
...  
Keyword(s):  
Continental Shelf ◽  
North Sea ◽  
Estimation Model ◽  
The North ◽  
Rock Formations ◽  
Novel Approach ◽  
Drilling Technology ◽  
Bottom Hole Assembly ◽  
The North Sea ◽  
Exploration Well

Abstract The southern part of the North Sea continental shelf is known for large intervals of hard, compact, cretaceous chalk formations that historically have proven to be challenging to drill through in one run. In recent years technology has been developed to drill specifically through these types of sedimentary successions as effectively as possible to be durable and competitive in similarly challenging drilling settings. Formations that previously would require multiple bit runs are now being drilled in one. The exploration well 2/9-6 S Eidsvoll, operated by MOL Norge AS, was drilled in this area of the North Sea continental shelf, with this specific type of chalk being drilled in the 12 ¼-in. section. Because the 12 ¼-in. section consisted of several different lithologies, it was vital to design the bottom hole assembly (BHA) to handle the diversity of rock formations to be drilled. Lithologies ranging from soft, swelling clay to hard compact chalk with an Unconfined Compressive Strength (UCS) as great as 20,000 psi were expected. In addition to managing the challenging drilling environment, determining the casing setting depth was of the highest priority because a pressure ramp was expected near the planned setting depth. This pressure ramp is located in the Base Cretaceous Unconformity (BCU), which is a well-known seismic reflector in the area. The top of this reflector had an uncertainty of ±75 m, which is not ideal following a decision to set the 9 ⅞-in. casing as near as possible to the reservoir. Seismic-while-drilling technology was applied to reduce this uncertainty and better tie-in the acoustic velocities to the pre-drilling seismic model. In addition, a geomechanics team was tasked with creating and updating the prognosed pore pressure estimation model. This information was important in making the mud-weight decision when drilling the 8 ½-in. section.

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