Rocksource ASA

Bergen, Norway

Rocksource ASA

Bergen, Norway
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Hartley A.J.,University of Aberdeen | Weissmann G.S.,University of New Mexico | Nichols G.J.,Royal Holloway, University of London | Warwick G.L.,University of Aberdeen | Warwick G.L.,Rocksource ASA
Journal of Sedimentary Research | Year: 2010

An analysis of remotely sensed imagery reveals that fluvial planform geometries within aggrading continental areas are dominated by distributive fluvial systems (DFSs). We documented the gradient, length, apex location, planform, termination type, and tectonic and climatic setting of 415 examples of fluvial systems which in planform display a radial, distributive channel pattern and have an apex-toe distance > 30 km (large DFSs). The longest of these DFSs is 704 km in length, with the majority (72%) ranging between 30 and 100 km in length. Gradients on individual systems range from 0.00003 (0.0018°) to 0.02656 (1.5°). Six planform types are recognized, those with: (1) a single braided channel that bifurcates downstream into braided and/or straight channels, (2) a single dominant braided channel, (3) a single dominant braided channel which becomes sinuous downstream often bifurcating, (4) a single dominant sinuous channel, (5) a single sinuous channel that bifurcates downstream into smaller sinuous channels, and (6) multiple sinuous channels. Of the studied examples 58% occur within exorheic basins and 42% in endorheic basins, with seven different termination types recognized. In many examples, channel planform changes downstream from a distributive pattern to a contributory pattern. In others, channels terminate at an axial fluvial system, at the coast, in eolian dune fields, playa lakes, permanent lakes, or wetlands. Large DFSs and their catchments are developed in all climatic regimes, including drylands, tropical, subtropical, continental, and polar climates. Large DFSs occur in all tectonic settings, including extensional, compressional, strike-slip, and cratonic tectonic regimes. General trends and relationships between the different studied parameters can be observed, leading to a broad understanding of the main controls on large DFS development. All of the planform types occur in all tectonic settings and all climate zones. Braided planforms dominate all tectonic settings, but particularly compressional regimes. High-gradient braided systems tend to be associated with areas of high relief and are well developed in dryland climates where discharge is inferred to be intermittent in comparison to tropical climates. Large DFSs with sinuous planforms do occur in dryland climates but tend to predominate in wetter, more tropical climates where discharge is more constant and the fluvial systems can distribute bedload more efficiently. Sinuous systems also tend to have significantly lower gradients than braided systems. Although these general observations can be made, there are significant variations from these trends, which are inferred to be controlled by variations in (1) discharge related to climate and (2) sediment supply, which is a function of climate, catchment size, catchment lithology, and catchment relief. Large DFS length is controlled by the available horizontal accommodation space, which in turn is strongly related to tectonic setting. The longest DFSs occur in peripheral foreland basins and cratonic settings where lateral systems can develop across an extensive basinwards slope. Extensional, strike-slip, and piggy-back basins are narrower and have much more limited horizontal accommodation space. Consequently DFSs developed in these settings are shorter, with radii often less than 30 km. DFSs dominate in aggradational settings such as actively subsiding sedimentary basins and therefore form a significant proportion of alluvial sedimentary successions preserved in the rock record. Copyright © 2010, SEPM (Society for Sedimentary Geology).

Kieft R.L.,Imperial College London | Kieft R.L.,British Petroleum | Hampson G.J.,Imperial College London | Jackson C.A.-L.,Imperial College London | And 2 more authors.
Journal of Sedimentary Research | Year: 2011

The upper part of the Almond Formation records the overall retreat of a wave-dominated shoreline and associated lagoons or bays. Exposures of these strata on the eastern flank of the Rock Springs Uplift, Wyoming, U.S.A., enable analysis of their stratigraphic architectures along sections oriented oblique to depositional strike. The upper Almond Formation comprises at least nine vertically stacked regressive-transgressive cycles. The regressive component of each cycle consists of thick (up to 22 m), laterally continuous wave-dominated shoreface and overlying coastal-plain deposits that occur in paleoseaward locations and have abrupt (< 400 m) paleolandward pinchouts. The transgressive component of each cycle consists of one or more bay-fill successions that occur in paleolandward locations and gradually thin in a paleoseaward direction. Transgressive bay-fill deposits in each cycle are thick (up to 18 m) and associated with preservation of surfaces that record, in progressively paleoseaward locations: initiation of a lagoon or bay (transgressive surface), erosional retreat of tidal-inlet channels (tidal ravinement surface) and the shoreface (wave ravinement surface), and marine flooding (marine flooding surface). This architecture records regression of a strandplain or wave-dominated delta, and subsequent transgression of a barrier island and spit with associated lagoon or bay. The occurrence of such thick and fully preserved bay-fill successions indicates that accretionary transgressive shoreline trajectories were developed. Strongly-aggradational-to-weakly- retrogradational stacking of successive regressive-transgressive cycles results in a layered stratigraphic architecture, with laterally continuous shoreface sandstone layers interbedded with bay-fill shale layers. Shoreface sandstones layers pinch out up-dip abruptly (< 400 m) into bay-fill shales and have limited vertical connectivity. Sandstones within bay-fill and coastal-plain deposits occur as small, laterally discontinuous bodies of variable geometry and connectivity. However, these sandstones may provide additional connectivity where they erode through bay-fill shales between two shoreface sandstone layers. © 2011, SEPM.

Fossen H.,University of Bergen | Schultz R.A.,University of Nevada, Reno | Rundhovde E.,Statoil | Rotevatn A.,University of Bergen | And 2 more authors.
AAPG Bulletin | Year: 2010

Segmented graben systems develop stepovers that have important implications in the exploration of oil and gas in extensional tectonic basins. We have compared and modeled a representative stepover between grabens in Canyonlands, Utah, and the North Sea Viking Graben and, despite their different structural settings, found striking similarities that pertain to other graben systems. In both cases, the stepovers represent relatively high parts within the graben systems that are likely to be among the first to be filled with hydrocarbons generated in deeper parts of the grabens. Furthermore, the relay ramps and smaller fault offsets in stepovers ease hydrocarbon migration and allow stepovers to act as preferred migration routes from deep graben kitchens to structurally higher traps in the basin. Graben stepovers and their related structures should be paid special attention during exploration because they may represent hydrocarbon accumulations complementary to larger traps along the graben flanks. These observations explain the location of the Kvitebjorn, Valemon, and Huldra fields in a stepover structure of the Viking Graben and encourage increased focus on similar graben stepovers in the Viking Graben and other graben systems. Copyright ©2010. The American Association of Petroleum Geologists. All rights reserved.

Jackson C.A.-L.,Imperial College London | Kane K.E.,Imperial College London | Kane K.E.,Statoil | Larsen E.,Statoil | Larsen E.,Rocksource ASA
Petroleum Geoscience | Year: 2010

3D seismic and well data are integrated to determine the tectono- stratigraphic evolution of the SW margin of the Utsira High, northern North Sea rift system. During the Triassic, a series of minibasins formed due to passive diapirism of the evaporite-bearing, Upper Permian, Zechstein Supergroup. Subsequently, during the Jurassic, a series of secondary minibasins developed as the underlying salt walls collapsed. These minibasins were a few hundred metres deep, bound by sub-circular to elongate salt-cored structural highs and caused the development of complex subaerial topography and submarine bathymetry on the SW margin of the Utsira High. Salt withdrawal may have been related to: (i) partial dissolution of salt; (ii) differential erosion of the salt walls and adjacent Triassic-filled minibasins; or (iii) salt remigration caused by sub- or supra-salt extension or sediment loading. This study provides insights into the tectono-stratigraphic evolution of the SW margin of the Utsira High and has implications for (i) facies distribution of the Zechstein Supergroup within the northern North Sea rift system; and (ii) depositional system development, and thus reservoir distribution, within the Jurassic sedimentary succession. © 2010 EAGE/Geological Society of London.

Jackson C.A.-L.,Imperial College London | Grunhagen H.,Statoil | Howell J.A.,University of Bergen | Howell J.A.,Rocksource ASA | And 7 more authors.
Journal of the Geological Society | Year: 2010

Three-dimensional seismic reflection data are used to image littoral deposits within the lower Brent Group, northern North Sea. Seismic attribute maps within the unit indicate the development of parallel, highamplitude stripes up to 15 km in length, 50-100 m wide and spaced 150-200 m apart. In map view these features trend NE-SW to ENE-WSW and are arranged into 'sets' that display subtly different orientations. Well data in regions where these anomalies are well developed indicate pronounced anomaly-perpendicular thickness variations in sand-rich beach-ridge facies within the Etive Formation and coals and mudstones within the overlying Ness Formation. Based on these observations, the high-amplitude anomalies are interpreted as the seismic expression of coal-filled swales, whereas the adjacent zones of low amplitude are interpreted to represent the cores of sand-rich beach ridges. The geometry of beach ridges identified in the Etive Formation compares favourably with sedimentological and geometric data from modern beach ridges. The results of this study have implications for (1) the stratigraphic context and preservation of beach ridges, (2) datum selection when attempting stratigraphic correlations within the Brent Group, and (3) the exploration and production of hydrocarbons from beach ridge-type reservoirs. © 2010 Geological Society of London.

Kieft R.L.,Imperial College London | Kieft R.L.,British Petroleum | Jackson C.A.-L.,Imperial College London | Hampson G.J.,Imperial College London | And 2 more authors.
Petroleum Geology Conference Proceedings | Year: 2010

The Middle Jurassic Hugin Formation has been the target of exploration within Quadrant 15 of the Norwegian South Viking Graben since the 1960s. The Hugin formation comprises shallow-marine and marginal-marine sediments deposited during the overall transgression and southward retreat of the 'Brent Delta' systems. Sedimentological analysis of cores across the quadrant has identified six facies associations: bay-fill, shoreface, mouth bar, fluvio-tidal channel-fill, coastal plain and offshore open marine. These facies associations are arranged in a series of parasequences bounded by flooding surfaces, several of which are correlated regionally using biostratigraphic data. Within this stratigraphic framework, facies association distributions and stratigraphic architectures are complicated, reflecting the spatial and temporal interaction of various physical processes (e.g. waves and tides) with an evolving structural template produced by rift initiation and salt movement. The overall transgression was highly diachronous, becoming younger from north to south. The northern part of the study area (Sigrun-Gudrun area) is characterized by a series of backstepping, linear, north-south-trending barrier shorelines and sheltered bays. The central part of the study area (Dagny area) contains stacked, backstepping strandplain shorelines that fringed syn-depositional topographic highs. Local angular unconformities are developed around these highs, implying that they formed above fault-block crests and salt-cored structures. The southern part of the study area (Sleipner area) contains stacked deltaic shorelines that were modified by both waves and tides. Sandbody geometry is closely related to depositional regime and syn-depositional tectonic setting within the basin; a robust understanding of both is critical to successful exploration of Hugin Formation reservoirs. © Petroleum Geology Conferences Ltd. Published by the Geological Society, London.

Hesthammer J.,Rocksource ASA | Hesthammer J.,University of Bergen | Stefatos A.,Rocksource ASA | Boulaenko M.,Rocksource ASA | And 5 more authors.
Marine and Petroleum Geology | Year: 2010

The use of the controlled source electromagnetic (CSEM) method as a risk reduction tool in marine hydrocarbon exploration is gaining increased acceptance in the oil industry. This is related to the ability to map resistivity contrasts in the sub-surface and thus aid the detection of hydrocarbons which are typically more resistive than surrounding rocks. Whereas acoustic (seismic) energy allows for mapping sub-surface structures that may contain hydrocarbons, electromagnetic (EM) energy can often say something about the fluids contained within the structures. Numerous successful CSEM case stories have been published over the past several years. However, there are also quite a few stories about "failure" -cases, although not well documented in the literature. Such "failure" -cases may reflect the lack of understanding of the CSEM technology and how CSEM data can act as a value driver. In order to understand this, it is necessary to handle uncertainties and decisions associated with the technology, These include geological uncertainties, noise models, survey designs, forward modelling parameters, inversion/migration parameters and pre-processing of real data. A proper handling of these uncertainties and decisions will aid in defining and constraining the chance of geologic success and geologic-success-case net present value for prospects prior to drilling wells. As such, the CSEM technology has a significant potential to increase exploration efficiency, if applied correctly. © 2010 Elsevier Ltd.

Somme T.O.,University of Bergen | Jackson C.A.-L.,Imperial College London | Vaksdal M.,Rocksource ASA
Basin Research | Year: 2013

In this study, we use seismic reflection, well and core data to investigate the role that basin physiography and sediment routing systems played on the distribution, geometry and stratigraphic architecture of Upper Cretaceous submarine fans (SF) offshore Norway. The Late Cretaceous Møre-Trøndelag margin of western Norway was characterised by steep submarine slopes (gradient of ~0.3°-3°). Mudstones dominate the Upper Cretaceous slope succession, although a few regionally extensive, sandstone-dominated units are developed. We focus on the most regionally extensive sandstone unit, which is of Late Turonian-to-Early Coniacian age. Mapping and visualisation of 2D and 3D seismic reflection data and analysis of well data indicates that the sandstone unit comprises a total of 11 SF, which were fed by sand-rich sediment gravity flows routed through multiple upper slope canyons. Based on the internal organisation of seismic facies, four fan types have been identified: (i) Type Ia fans, which are characterised by <10 erosional channel complexes at their bases and aggradational to landward-stepping lobes in their upper parts; (ii) Type Ib fans, which are characterised by >10 erosional channel complexes at their bases and aggradational to landward-stepping lobe and mass-transport deposits near the fan apex in their upper parts; (iii) Type II fans, which are dominated by aggradational lobe deposits; and (iv) Type III fans, which are dominated by a single channel complex that passes downdip into a small terminal lobe. The different fan types are interpreted to reflect variable stratigraphic responses to source proximity and basin physiography, which is principally related to the degree of local fault reactivation and differential compaction. This variability highlights the diversity of fan types that may occur over short distances along continental margins, and demonstrates the importance of local controls in understanding the internal stratigraphic variability that may be present in deep-marine successions. © 2012 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists.

Alaei B.,Rocksource ASA
Fault and Top Seals: From Characterization to Modelling | Year: 2012

Seismic attributes have been utilized to enhance identification and mapping of faults on seismic volumes. Application of 3D seismic attributes together with advanced visualization techniques allow combination of different fault characteristics and result in a better understanding of complex fault systems. In this study fault attribute analysis is integrated with frequency decomposition process. A fault imaging workflow including structurally oriented semblance attribute volume and fault enhancement attribute volumes have been generated using two different sets of seismic input. First the fault imaging workflow was carried out using full band seismic volume. Then, seismic data has been decomposed into amplitude volumes representing individual frequencies. The same fault imaging was repeated using amplitude volume from high frequency. Amplitude volumes of higher frequencies correspond to higher resolution. The method has been tested on a 3D dataset from the Mid Norwegian Sea. The results show that using amplitude volumes of higher frequencies can image smaller scale faults that are not visible using full band seismic volumes as input for the fault imaging. Improved fault imaging achieved using this method can help derisk fault seal related issues in areas with complex structural setting such as the one presented in this study.

Sperrevik S.,Rocksource ASA | Rykkelid J.I.,Rocksource ASA | Hesthammer J.,Rocksource ASA | Cumming D.,Rocksource ASA | And 5 more authors.
Hart's E and P | Year: 2011

A case study from the Norwegian Continental Shelf (NCS) demonstrated the potential of controlled-source electromagnetics (CSEM) technology's ability to identify new prospectivity in an explored basin. Rocksource ASA is a E&P company from the country that focused significantly on the use of CSEM technology and its integration into the exploration workflow. The company was awarded 60% of license PL 559 in the APA 2009 licensing round on the NCS where feasibility studies showed that the prospectivity from several different reservoir intervals needed to be feasible for reducing risk with CSEM data. Proprietary CSEM and seismic data were used as part of an integrated approach to test and de-risk the identified prospectivity.

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