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 Predictive stratigraphy developed in the 1950s and 60s through the breakthrough work of Larry Sloss and Harry Wheeler. The major change from previous work was an understanding of time stratigraphy and major breaks in stratigraphic sequences. With the advent of new technology, such as high-resolution logging, coring, seismic, and remote sensing, succeeding decades were dominated by drastic progress of new methods and geological understanding, namely facies analysis and seismic and sequence stratigraphy. Offshore exploration required predictive methods to be developed because wells in these basins had very high costs in contrast to onshore basins and were technically very challenging to drill, so that offshore basins and plays were best investigated using “remote” methods. Seismic and sequence stratigraphy are extremely powerful techniques for understanding the fill of sedimentary basins but have been incorporated to a lesser degree in onshore sediment source areas. A common theme for breakthroughs in geology has been the development of new technology. Many new concepts have developed in the wake of new geophysical methods. Remote sensing technology using satellites came into the public domain in the 1990s after the large military campaigns during the 1980s. This was a quantum leap in the ability to retrieve quantitative geomorphic and topographic data efficiently from onshore regions. While classic geomorphological techniques had been in use for decades, they were largely analog and constrained to analysis of topographic maps. Digital onshore data allowed for breakthrough analysis of onshore geomorphology, drainage, bedrock, and water and sediment flux to offshore basins. The ability to combine the quantitative onshore data with offshore data (such as seismic) allowed for a new predictive methodology to develop based on semiquantitative and integrated analysis of entire, linked onshore and offshore systems. The technique, termed source-to-sink, built on studies from the early 1980s regarding sediment flux to modern offshore basins. The early techniques, however, did not consider stratigraphy and had little predictive power. Various source-to-sink methods developed, both experimental computer-based modeling, and geomorphic-based, but initial methods were not tuned to be used in exploration due to using data and methods not suited and aligned to conventional exploration data. A simpler more morphological approach thus developed that allowed for predictive analysis based on onshore remote sensing data and conventional offshore seismic. Source-to-sink analysis complements sequence stratigraphy rather than replacing it. Detailed analysis of basin fill sequences based on seismic and well data requires sequence stratigraphic analysis, but this analysis is augmented by a wider view including the onshore sediment-generating area. A new development with source-to-sink analysis was the ability to use the methodology on outcrop data. This required the ability to measure, calculate, and/or interpret critical data from the outcrop sequences, such as slope lengths. Extensive offshore exploration in some basins has allowed for almost basin-wide coverage of 3D seismic data. Merging these data sets lifts predictive stratigraphy and source-to-sink to a new level. It is now possible to visualize entire source-to-sink systems, also including antecedent onshore drainage systems as well as their offshore complementary sequences. Increased efficiency and precision in subsurface and seismic interpretation allow for incisive perspectives on quantitative aspects of these source-to-sink systems. Thus, new understanding of complete systems will likely develop as a response to these extremely extensive seismic data sets where “everything” can be seen.

Abstract High-resolution seismic stratigraphic and geomorphic analysis reveals the evolution of a shelf to intraslope basin on the Santos Basin continental margin, offshore Brazil. Within a late Cretaceous framework of high confidence 3D-seismic-stratigraphic correlations, exceptional quality seismic-geomorphic beach-ridge-, canyon-, channel- and lobe-elements are analyzed with particular focus on their temporal and spatial relations. Shallow and deep marine, partly gravity-driven processes associated with depositional outbuilding of the continental margin generate local gradients and sea-floor topography that determine cyclic changes in aggradational and degradational patterns. This is manifested in the proportion, distribution, size, shape and orientation of shoreline, shelf edge, canyon, slope-channel and intraslope submarine fan depositional elements. The evolution of the continental margin is a response to the dynamic changes in sediment delivery, shelf accommodation, local slope gradient, seafloor topography, and mobile salt substrate geometry. The study documents significant sandy submarine fan deposition development along an over-all high accommodation margin, typically associated with higher frequency episodes of relatively low shelf accommodation expressed as normal progradation, flat shoreline trajectory, and narrow (<10km width) shelf development. Genetically connected, continuous sediment fairways develop and span from beach-ridge/shore-face systems via combined shelf/slope positioned canyon to intraslope basin submarine fan systems. Longshore drift and/or storm re-suspension processes is inferred to deliver sandy sediment to shelf-portion of submarine canyon. Farther down-dip transport and deposition is driven by gravity flows. The observed (wide) longitudinal to lateral aspect ratio (~10 km × ~20 km) is explained as a direct response to the salt-influenced intraslope basin topography, as well as significant lateral-directed drive to fan growth relative to basin-restricted longitudinal (downdip) growth. Negative shelf accommodation manifested by subaerially incised valley(s) features are not observed and is thus not a necessity for submarine fan development.