The Discovery

On 26th March 1993, the discovery well 15/9-19 SR was up for completion and production testing.  The well produced at a maximum rate of 1358 m³/d. This was the turning point for a journey, that started in 1976, when the Block 15/9 along with Block 15/8 was awarded the Production License (PL) 046.

Image 1: Location of the 15/9-19 SR well and the Theta Vest Structure

A drill stem test had been carried out between the interval, 2863.6 – 2880.5 m TVD MSL. The permeability estimated from the build-up analyses was approximately 914 mD and the extrapolated reservoir pressure was calculated to be around 327.7 bar.

The distribution of the block ownerships:

Statoil (operator)	52.6%
Esso	28.0%
Norsk Hydro	9.4%
Elf	9.0%
Total	1.0%

The primary objective of the well was to test the hydrocarbon potential in the Heimdal Formation of Paleocene age, which is the main reservoir in the Sleipner Øst area while the secondary objective was to test the hydrocarbon potential in sandstones of Jurassic/Triassic age. However, the secondary objective led to the fortuitous encounter of oil in the Middle Jurassic Hugin Formation (Image 2).

Image 2: Structural cross-section along the 15/9-19 SR well path

The 18 meters thick Hugin Formation was found to be completely filled with hydrocarbons to its base at 2882.0 m MSL.

The Theta Vest structure and the oil trap is a dome-shaped structure. This trap has a well-defined spill point to the east and is, best case, believed to be filled down to this point. However, several faults cutting the crest of the structure are thought to be sealing off, the hydrocarbon accumulation, from spilling eastwards.

The core logging, covering the lower part of the Middle Jurassic Hugin Formation and the uppermost part of the Triassic Skagerrak Formation, indicates a high frequency of fractures in the cores. This suggests the penetration of a zone of intense and complex faulting. The application of a pure or simple shear model gives an unfaulted thickness in the range of 24 to 27 meters. (Explained in the next blog).

The petrophysical analysis of the Hugin Formation in the 15/9-19 SR well results in a mean net/gross of 0.924, porosity of 22.6%, permeability of 2913.2 mD and water saturation of 11.0%.

The most probable resource estimate for the Hugin reservoir in the Theta Vest structure is 10.33×10⁶ Sm³ oil in place and 1.65×10⁹ Sm³ associated gas phase in place. A recovery factor of 45%, leaves us with 4.55×10⁶ Sm³ of recoverable oil and 0.72×10⁹ Sm³ of recoverable associated gas phase.