Late Jurassic—early Cretaceous caprocks of the southwestern Barents Sea: fracture systems and rock mechanical properties

Gabrielsen, Roy H.; Kløvjan, O.S.

doi:10.1016/s0928-8937(97)80008-2

Cited by 32 publications

(11 citation statements)

References 12 publications

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“…1a), the effects of regional uplift of the margins were acknowledged already in the early 20th century (Reusch, 1901a;Nansen, 1922), but has recently received renewed attention, partly because the effects of the uplift influenced hydrocarbon prospectivity (e.g. Nyland et al, 1992;Doré and Jensen, 1996;Riis, 1996;Gabrielsen and Kløvjan, 1997;Chalmers and Cloetingh, 2000;Japsen and Chalmers, 2000;Cloetingh et al, 2005). It is also realized that the uplift and its shifting character through time has influenced not only the development of the present relief and morphology, but also the provenance of sediments and sedimentation pattern in the offshore basins (Faleide et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Latest Caledonian to Present tectonomorphological development of southern Norway

Gabrielsen

Faleide

Pascal

et al. 2010

Marine and Petroleum Geology

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Section: Introductionmentioning

confidence: 99%

Latest Caledonian to Present tectonomorphological development of southern Norway

Gabrielsen

Faleide

Pascal

et al. 2010

Marine and Petroleum Geology

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“…The Skrugard structure is one of several fault blocks in the area (Figs 2 and 3) and is part of the fault complex (Gabrielsen et al, 1990). The major regional fault zones in the Barents Sea were probably established by the Carboniferous (Gabrielsen and Kløvjan, 1997). After Carboniferous structuring and following a tectonically quiet period in the Triassic, block-faulting began in the Middle Jurassic.…”

Section: Geological Setting and Stratigraphymentioning

confidence: 99%

“…Fault activity increased from the Late Jurassic and into the Early Cretaceous, resulting in the formation of the major basins and highs. Towards the end of the Cretaceous, reverse faulting and folding, combined with extensional faulting in some areas, became locally signifi cant although subsidence continued on a regional scale (Gabrielsen and Kløvjan, 1997). Inversion peaked in the early Tertiary and was followed by intense regional uplift and erosion (Manum and Throndsen, 1978;Riis and Fjeldskaar, 1992;Nyland et al, 1992;Doré and Jensen, 1996;Gabrielsen and Kløvjan, 1997;Cavanagh et al, 2006;Ohm et al, 2008).…”

Section: Geological Setting and Stratigraphymentioning

confidence: 99%

Geochemical Characteristics of the Skrugard Oil Discovery, Barents Sea, Arctic Norway: A “Palaeo‐biodegraded – Gas Reactivated” Hydrocarbon Accumulation

Matapour

Karlsen

2017

Journal of Petroleum Geology

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This paper investigates the filling history of the Skrugard and Havis structures of the Johan Castberg field in the Polheim Sub‐Platform and Bjørnøyrenna Fault Complex, Barents Sea (Arctic Norway). Oil and gas occurs in the Early Jurassic and Middle Jurassic Nordmela and Stø Formations at Johan Castberg, and both free oil and bitumen are interpreted to be sourced from the Upper Jurassic Hekkingen Formation (Kimmeridge Formation equivalent). The geochemical characteristics of the petroleum from Skrugard and Havis, including the GOR, API and facies and maturity signatures, can be understood within a complex fill history which includes a palaeo oil charge, Tertiary uplift (>2 km), dismigration, in‐reservoir biodegradation, and late‐stage refill with gas. The API and GOR of the Skrugard oil are 31° and 60m3/m3, respectively. The petroleum is geochemically similar to that in the nearby Havis structure, to that in the Snøhvit region to the south of the Loppa High, and also to the petroleum recorded as traces in well 7219/9‐1, approximately 16 km SW of Johan Castberg field. However, the petroleum differs from the oil in the Alta well 7120/2‐1, located in the southern part of the Loppa High, illustrating the complexity of the regional petroleum systems. The Skrugard oil is of medium maturity (ca. 0.8–0.9% Rc), and is significantly biodegraded despite being gas‐saturated. Evidence for biodegradation includes the reduced concentrations of C10‐C25 n‐alkanes and the presence of a prominent unresolved complex mixture (UCM) in gas chromatogram traces. However non‐biodegraded C4‐C8 range hydrocarbons are also present in the reservoir. This suggests a recent charge of gas/condensate into the structure which therefore contains a mixture of palaeo‐degraded and unaltered petroleum. Oil‐type inclusions within authigenic quartz and feldspar from reservoir sandstones at Skrugard were analysed. The results indicate that the structure (present‐day depth 1276–1395m) underwent Tertiary uplift by ca. 2–3km following an earlier phase of oil emplacement. The presence of the oil type inclusions, both in the current gas zone (Stø Formation) and in the oil zone (Stø and Nordmela Formations), indicates that the positions of the oil‐water and gas‐oil contacts have changed over time. This is consistent with a recent gas charge to the upper part of the reservoir, and also with the gas being at dew point. These observations are supported by analyses of core extracts which show an increasing bitumen content towards the OWC, and the oil‐type bitumen in the present‐day gas zone. A charge history model for the Skrugard structure is proposed which integrates both the observations concerning the petroleum inclusions and the biodegraded oil together with observations of seismically‐monitored gas fluxes along the rim of the Loppa High. Improved understanding of the Skrugard structure and its filling history will assist exploration in similar settings in other parts of the Barents Sea and worldwide, particularly where multiple source rocks and a multi‐stage ...

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“…million years) up to Tertiary periods. During the Cretaceous period, the area experienced compression with reverse faulting and folding, combined with extensional faults in some areas (Gabrielsen and Kloevjan 1997). The most significant exploration problem in the Barents Sea is related to the severe uplift and erosion in the range of 500-2000 m that took place during the Tertiary period (Dore 1995).…”

Section: Introductionmentioning

confidence: 99%

“…Pre-existing fractures have been identified in these formations in core studies (Gabrielsen and Kloevjan 1997 (Nygaard et al 2006). When fractures are hydraulically open, losses may occur if the mud weight is higher than the pore pressure gradient.…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation of fracture width limitations of granular lost circulation treatments

Alsaba

Nygaard

Saasen

et al. 2016

J Petrol Explor Prod Technol

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Drilling fluid losses into fractured shales is a major challenge. Lost circulation treatments are widely applied to mitigate the losses; however, the effectiveness of these treatments is affected by different physical properties of the used lost circulation materials (LCM). This paper presents an experimental investigation to study the effect of LCM type, concentration, particle size distribution, temperature, and LCM shape on the formed seal integrity, with respect to differential pressure, at different fracture widths. The overall objective of this study is to address the effectiveness of LCM treatments in sealing fractured shales, with specific application to the over consolidated Barents Sea overburden. Three commonly used LCMs that vary in size were used to formulate and evaluate the effectiveness of nine LCM blends. Nutshell blends effectively sealed different fracture widths with high seal integrities. Examination of the formed seal under an optical microscope and a scanning electron microscope revealed that this performance is due to the irregular shapes of these materials as well as their ability to deform under elevated pressure. Based on the results, it has been found that to effectively seal fractures using granular LCM treatments, the D90 value should be equal or slightly larger than the anticipated fracture width. However, due to both the increased risk of plugging downhole tools and the availability of larger LCM, granular LCM treatments can only be used to seal fractures up to 2000 microns. With the current limitations, other unconventional treatments are required to seal fractures wider than 2000 microns.

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Late Jurassic—early Cretaceous caprocks of the southwestern Barents Sea: fracture systems and rock mechanical properties

Cited by 32 publications

References 12 publications

Latest Caledonian to Present tectonomorphological development of southern Norway

Latest Caledonian to Present tectonomorphological development of southern Norway

Geochemical Characteristics of the Skrugard Oil Discovery, Barents Sea, Arctic Norway: A “Palaeo‐biodegraded – Gas Reactivated” Hydrocarbon Accumulation

Experimental investigation of fracture width limitations of granular lost circulation treatments

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