Late Cenozoic depositional history of the Danish North Sea Basin: implications for the petroleum systems in the Kraka, Halfdan, Siri and Nini fields

Abstract

The CentralGrabenarea wasfilled withathick pileofsediments duringthe MiddleM ioceneQuaternary,correspondingto aperiodof15Ma.Ashydrocarbon expulsion from the most prolific source rock, the UpperJurassic BoMember,wasinitiated only 20 Ma BP andstill occurs today,the MiddleM ioceneQuaternary evolution isimportant.Int he MiddleMiocene, the CentralGrabenarea wascovered byasea with waterdepthof500 -700 m. Duringthe LateMiocene(Tortonian),the basinwassuccessively filled byprograding slopeanddeltaic sedimentsfrom the northeast. The progradationalinfill resulted inlocaltiltingofthe substratum dueto the loadinge ffecto fthe deposits. Int he latest LateM iocene(Messinian),the maininput ofsediments occurred from the south, asillustrated byathick onlappingsuccession ofupperMessiniansediments. Pliocene sedimentation wascharacterized byr egularinfill from the east withinashelfto shallow marined epositional environment.Followingthe Miocenea ndP liocene, the NorthS ea Basint ilted dueto stronguplifto fthe Fennoscandians hielda ndi ncreased subsidence andsedimentation ratesw ithint he CentralGrabenarea.This furthercomplicated the maturation ofthe source rock, migration pathways anda ccumulation ofh ydrocarbons. The consequence ofthiscomplexburialhistory isexemplified bythe Kraka andHalfdanfields. The Kraka Field hasalarge down-flankoilaccumulation,which ist he result ofaporosity anomaly resultingf rom anearly invasion ofoilint hisp osition beforethe latetiltingofthe NorthS ea Basin. The history ofthe non-structural accumulation ofthe HalfdanFieldcanbe readily modelled;itconstituted asimplefour-waydipclosureduring the LateMiocenewhenpeak oilmigration occurred.The Quaternary tiltingofthe NorthSea Basindueto upliftof the FennoscandianShielda ndstrongsubsidence ofthe CentralGrabenarea resulted inad istinctgradient favouringlong-distance migration ofhydrocarbons. The occurrence ofviablemigration routes,especially within Paleocenesandlayers,hasresulted inlong-distance migration ofoilinto the Sirisubmarinevalleysystem. The most northern indication ofh ydrocarbons hasbeenr ecognized asfaras7 5kmfrom the source area.Longdistance migration ofh ydrocarbons isalso indicated bydirecthydrocarbon indications( DHIs) throughoutt he Cenozoic succession int he DanishN orthS ea.DHIsareparticularly prominent abovek nown hydrocarbon accumulationsint he CentralGraben. Thisindicatesp ronounced verticalm igration,f or instance alonga ctive faults,abovethesestructures.

The early Quaternary North Sea Basin

“…The chronostratigraphy of Kuhlmann et al (2006) in Dutch exploration well A15-03 (55°18′N, 3°48′E; Fig. 1) can be correlated to the work of Köthe (2007Köthe ( , 2012 and Thöle et al (2014) in the German sector of the North Sea, Nielsen et al (2008) and Rasmussen et al (2005) in the Danish sector, and Noorbergen et al (2015) onshore Netherlands (Table 1; Harding 2015). The correlation provides a robust calibration across the topsets of the clinoform system, beyond the reach of the southern North Sea regional unconformity.…”

“…This method correlated the two through the locally extensive unconformity at the top of the Upper Miocene to Lower Pliocene Utsira Formation, but this relationship assumes that middle to late Pliocene deposits are absent, which is not the case (Eidvin et al 1999). Towards the southern half of the basin the Quaternary is preceded by an extensive Pliocene wedge (Cameron et al 1992;Rasmussen et al 2005;Thöle et al 2014;Harding 2015; Table 1). …”

Fluid flow features in hydrocarbon plumbing systems: What do they tell us about the basin evolution?

“…Lateral migration through the sand filled Siri Canyon represents a second major fluid migration route in the Danish Central Graben area as documented by many studies (e.g. Hamberg et al, 2005;Rasmussen et al, 2005;Svendsen et al, 2010). Lateral migration of hydrocarbons through the Siri Canyon was also suggested to facilitate the formation of the mid-Miocene sand volcano (Andresen et al, 2009).…”

A giant (5.3×107m3) middle Miocene (c. 15Ma) sediment mound (M1) above the Siri Canyon, Norwegian–Danish Basin: Origin and significance

“…Cenozoic deposits in the Norwegian-Danish Basin including the Siri Canyon infill were mainly derived from the eastern basin margin, and were controlled by tectonically and climatically controlled relative sea level changes and shifts in sediment source areas (Michelsen et al, 1998;Huuse, 2002;Rasmussen et al, 2005). An overall upward coarsening of the Cenozoic succession (Kristofferson and Bang, 1982;Schiøler et al, 2007) reflects progradation of the eastern basin margin which resulted in a progressive narrowing of the North Sea Basin during the Cenozoic (Ziegler, 1990;Huuse, 2002).…”

“…The mid-Miocene unconformity was flooded during a widespread transgression, the so-called Hodde transgression, in response to a minor eustatic rise c.1 Myr before the onset of the longterm mid-Miocene eustatic lowering at c. 15 Ma (Huuse and Clausen, 2001;Huuse, 2002). During deposition of the Hodde Formation, climate was relatively warm and sea level was significantly higher than today, with water depths in the Central Graben area being of the order of 200-500 m (Laursen et al, 1997;Huuse, 2002;Rasmussen et al, 2005). Sedimentation rates during the Hodde transgression were low and the Hodde Formation is thus composed of transgressive marine clays with only minor sand layers (Schiøler et al, 2007).…”