Sedimentology and sequence stratigraphy of the Middle–Upper Jurassic Krossfjord and Fensfjord formations, Troll Field, northern North Sea

Abstract

The Middle-Upper Jurassic Krossfjord and Fensfjord formations are secondary reservoir targets in the super-giant Troll oil and gas field, Horda Platform, offshore Norway. The formations comprise sandstones (c. 195 m thick) sourced from the Norwegian mainland to the east, that pinch out basinwards into offshore shales of the Heather Formation to the west. Sedimentological analysis of cores from the Troll Field has identified six facies associations, which represent wave-and tide-dominated deltaic, shoreline and shelf depositional environments. Resulting depositional models highlight the complex distribution of depositional environments, and reflect spatial and temporal variations in physical processes at the shoreline, rate of sediment supply and accommodation development. These models are further complicated by the absence of coastal plain facies, which implies that the Troll Field was fully subaqueous during deposition, that shoreline regression was forced by falling sea level or that coastal plain deposits were removed by transgression. Genetic sequences bounded by major flooding surfaces ('series') exhibit laterally uniform thicknesses, implying no major tectonic influence on sedimentation. The recognition of pronounced variability in facies character and stratigraphical architecture emphasize the need for a robust depositional model of the formations in order to drive future exploration in these, and coeval, reservoirs.

Impact of silica diagenesis on the porosity of fine‐grained strata: An analysis of Cenozoic mudstones from the North Sea

“… (a) Simplified structural map of the North Viking Graben, northern North Sea, highlighting the major faults, the Horda and East Shetland Platform [after Holgate et al ., ], (b) quantitative X‐ray diffraction data of exploration well 35/10‐1, (c) quantitative X‐ray diffraction data of exploration well 35/11‐5 with simplified stratigraphic column [ NPD , ], and (d) geoseismic section illustrating the major faults and stratigraphic units. Note that there are several stratigraphic breaks in the Cenozoic [e.g., Løseth et al ., ; Eidvin et al ., ] that are not annotated on these stratigraphic columns.…”

“…(a) Simplified structural map of the North Viking Graben, northern North Sea, highlighting the major faults, the Horda and East Shetland Platform [afterHolgate et al, 2013],…”

Clinoforms and clinoform systems: Review and dynamic classification scheme for shorelines, subaqueous deltas, shelf edges and continental margins

“…4). Clinothems have also significant storage potential for oil, gas, water and CO 2 , and several hydrocarbon fields rely on intra-clinothem reservoirs units (e.g., Sydow et al, 2003;Cummings and Arnott, 2005;Holgate et al, 2013;Patruno et al, 2018, in press). Since most clinoforms are lined by low-permeability mudstones or cements (Holgate et al, 2014), they often act as baffles to hydrocarbon flow (Howell et al, 2008;Jackson et al, 2009;Graham et al, 2015aGraham et al, , 2015b.…”

Kinematics of Polygonal Fault Systems: Observations from the Northern North Sea

“…The co-existence of silica diagenesis and polygonal fault systems in other basins (Davies FIGURE 2 | (a) Simplified structural map of the North Viking Graben, North Sea, highlighting major faults; the Horda, East Shetland Platform and Utsira High (after Holgate et al, 2013) al., 2006) has led some authors to suggest a genetic link between polygonal faulting and diagenesis (Shin et al, 2008;Davies et al, 2009;Cartwright, 2011;Davies and Ireland, 2011). It is thus worth noting that the transformation from opal-A to opal-CT probably migrated upward through the lower Hordaland Group, initiating in the Middle or Late Eocene and continuing, potentially, to the present (Wrona et al, 2017a).…”