A closer look at Mol’s multi-level discoveryDeep weathered and fractured basement rock (mangerite), hammer for scale. Photo: Terje Solbakk.

A closer look at Mol’s multi-level discovery

The northern part of the Utsira High comprises a complex level of reservoirs.

Yesterday’s announcement of the wildcat 25/8-19 S and the appraisal well 25/8-19 A reported a hydrocarbon discovery. But, not in the primary targets of Mol Norge and the PL 820 S, the prospects named Evra and Iving. Both prospects came in water-wet. However, the secondary targets delivered.

The story seems complex.

The wildcat was spudded on November 2, 2019, with the appraisal on New Year’s Eve. The operation took approximately 4.5 months, and the rig Deepsea Bergen is still on the location. The preliminary volumes given are between 13 and 70 MMboe.

The Late Triassic Skagerrak Formation was the main discovery level, with additional hydrocarbons proven in the Palaleocene Heimdal Formation, the Lower Jurassic Eriksson Formation, and in weathered and fractured basement rocks.

Overview of the Balder – Jotun area. Map: norskpetroleum.no.

The neighbour area hosts both the Balder field, including closest neighbour Ringhorne and the Jette, Jotun field and 25/8-16 S (Eitri) discoveries and others. Hydrocarbons are found at several levels in this northern part of the Utsira High, the most common shown in the table below.

Levels with hydrocarbons found in and near the Mol wildcat discovery 25/8-19 S.

Lithology

Lithological chart modified from the Norwegian Petroleum Directorate (Lithological chart of the North Sea). The yellow colour indicates sandstone proven in the wells 25/8-19 S and A.

The Basement is a quite broad term on the Norwegian Continental Shelf, it usually encompasses all rocks older than the Devonian. From the nearby well 25/10-2 R, basement rocks were also encountered, interpreted as of probably magmatic (syenite). The basement rock itself is likely of a Caledonian age, or older.

The weathering and fracturation of the basement are likely to be younger, possibly of a Triassic age as seen further south on the Utsira High. Such basement reservoirs can exhibit very good reservoir properties, as seen in the 16/1-15 (Tellus) discovery, now part of the Edvard Grieg field. Also, Hurricane’s Lancaster field on the UKCS produces from fractured basement rocks.

The Skagerrak Formation of the Hegre Group is usually composed of interbedded conglomerates, sandstones, siltstones and shales, deposited in prograding alluvial fan system.

The Eriksson Formation (and water-wet Nansen Formation) are part of the Statfjord Group, which exhibits a transition from continental to shallow marine sediments. In this area, the group consists of massive, white, fine to coarse-grained sandstones inter-bedded with silty shales.

The Heimdal Formation is the most common reservoir in the area. This unit is dominated by thick units of poorly sorted, fine to coarse-grained, poorly cemented sandstones, deposited on a shallow-marine shelf under high-energy conditions.

Injectites of Eocene age are also common in this part of the North Sea. Injectites are deposited following the mobilization of buried, waterfilled, unstable sand that migrate upwards into overlying sedimentary units.

Five Mini-Drill stem tests

In the press release, the Norwegian Petroleum Directorate writes that Mini-DSTs (pressure and fluid samples) have been carried out in both the injectites in the Eocene, in the Heimdal Formation, the Eiriksson Formation, the Skagerrak Formation and in the basement.

Further, a formation test was performed in the Skagerrak Formation in the appraisal well. The test yielded maximum respective oil and gas production rates of three Mboe and 475 Mboe per flow day through a 32/64-inch nozzle opening, according to the NPD.

The formation test revealed moderate flow properties. Water was not produced during the test.

TERJE SOLBAKK

 

 

 

 

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