ABSTRACT In April 2011, Statoil (Equinor from 2018), with partners Eni Norge and Petoro, discovered oil in the Skrugard prospect in the Barents Sea. An 83 m (272 ft) column of 32 API oil with a minor gas cap was proven in 350 m (1150 ft) thick sandstones with excellent reservoir properties. Skrugard was the second and by far the largest commercial oil discovery in the Barents Sea at that time. Ten months later, the adjacent Havis prospect proved a 127 m (417 ft) column of 35 API oil and similar volume of recoverable oil as Skrugard. Together they make up the main pools of the Johan Castberg Field. The tested traps were rotated fault blocks with Early to Middle Jurassic shallow marine and fluvial sandstone reservoirs, capped by Late Jurassic and Early Cretaceous shales and sourced from Late Jurassic marine source rocks. In the early exploration efforts in the western Barents Sea from 1987 to 1992, five exploration wells had tested similar prospects. All of them were dry, most with oil shows, and were interpreted to have leaked during Late Cenozoic uplift and erosion. Multiple episodes of glaciations during the last 2 million years with substantial erosion, associated tectonic tilting, and oscillations in reservoir pressure conditions have traditionally been regarded as the main cause of the failures. For many years, the leakage problems riddled Barents Sea exploration, reducing exploration activity substantially. This part of the Barents Sea was abandoned by oil companies because of the disappointing results. In addition, a stop in new area license awards in the Barents Sea was imposed by the authorities from 1997 to 2006, pending results of an environmental impact study. This, in combination with the general downturn of the industry, left the area without new exploration wells for 20 years. Following the lift of the moratorium in 2006, new evaluation based on 2-D seismic in the area identified that several prospects had seismic flat spots, but the volume potential was assessed to be limited. In 2008, WesternGeco acquired the first 3-D seismic survey of the area. Numerous prospects were mapped showing strong seismic hydrocarbon indicators, high volume potential, and high probabilities for discoveries. This resulted in Statoil and Eni Norge applying for a license in the 20th exploration round in 2008. Continued exploration in the license has been supported by the extensive use of integrated geophysical studies using 3-D seismic, Ocean Bottom Seismic, and 3-D Controlled Source Electromagnetic data. The Skrugard and Havis discoveries have been followed by an exploration program of eight additional wells so far, all of which are discoveries. The Johan Castberg field reserves are 556 MMbbl (88.7 MSm3) of recoverable light oil with an estimated plateau production at 190,000 barrels (30.000 Sm3) per day.

ABSTRACT The Middle Jurassic Brent Group of Northwest Hutton Field includes recently recognized incised valley systems in the Etive and Ness formations. These valleys were cut during relative sea-level falls and back-filled during subsequent rises. Valley-fills comprise mixed fluvial-tidal and purely fluvial rocks. Their grain size, orientation, and geometry contrast markedly with volumetrically greater highstand shoreface and delta mouth bar sheet sandstones. The valley-fills have significantly influenced production history of the field. Published data from other Brent Group fields allows correlation of sequence boundaries semi-regionally. Incised valley-fills range from 1.5 to 15 km in width and appear to have been focused on the Northwest Hutton area through time. Similarly other Brent Group fields appear to have occupied interfluve positions at successive sequence boundary times. This observation reconciles historical conflicts over the presence of sequence boundaries in the Brent province, with some fields having only subtle expressions of these key regional surfaces. Comparison of Brent incised valleys with well exposed examples from the Book Cliffs, Utah increases confidence in valley-fill interpretation and allows prediction of likely ranges of geometry and fill type in undrilled areas. The Book Cliffs example also raises the issues of the nature and location of possible lowstand deposits in front of the Brent delta.