--> Abstract: Chemostratigraphic correlation of Cretaceous and Tertiary sequences west of the Loppa High, Western Barents Sea, by T.J. Pearce and J.H. Martin; #90130 (2011)

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Chemostratigraphic correlation of Cretaceous and Tertiary sequences west of the Loppa High, Western Barents Sea

T.J. Pearce and J.H. Martin
Chemostrat Ltd., Unit 1, Ravenscroft Court, Buttington Cross Enterprise Park, Welshpool, Powys, SY21 8SL, U.K

Cretaceous and Tertiary marine sequences from the Western Barents Sea basin are increasingly being targeted for hydrocarbon exploration. However, the lack of well control, marked lateral facies and thickness variations, plus the lack of sediment dispersal maps, all contribute to the difficulty in correlating and ultimately mapping areas, with more favourable reservoir quality.

A pilot chemostratigraphic study has been undertaken to improve the correlation of the Cretaceous and Tertiary sequences, and to aid in reconstructing the history of sediment input into the basin. The current study wells lie to the west of the Loppa High, within the Sørvestsnaget, Trømso and Harstad basins (Fig. 1); an area which underwent rapid subsidence in the Cretaceous, with recent exploration targeting sands around the flanks of the Loppa High, which was uplifted and eroded during this time. This study builds on the regional correlation of twenty four wells from the Barents Sea (from the Loppa high and to the east), which focused on Triassic, Jurassic and in some wells, Cretaceous sequences.

The chemostratigraphic zonation is largely based on fluctuations in element concentrations that reflect changes in the abundance of: feldspar, clay minerals, heavy minerals and opaque minerals (corroborated by data acquired via mineralogical analyses), which themselves ultimately reflect variations in: provenance, volcanic input and palaeoclimate.

The study intervals can be divided into six sequences which can be correlated back to the Barents Sea study, as follows: Sequence S1 equates to the Early to Mid Jurassic formations, with S2 corresponding to the Late Jurassic Hekkingen Formation; S3 equates to the Early Cretaceous formations whilst S4 corresponds to the Late Cretaceous Kveite Formation; Sequence S5 equates to the Torsk Formation and S6 incorporates successions assigned to the Tertiary, Nordland Group (Fig. 1). These sequences are again divided into several packages which can be traced across the study area illustrating truncation and sediment on-lap onto the Loppa High.

The chemostratigraphic package correlation incorporating wells 7316/5-1, 7216/11-1 and 7117/9-2 is further integrated with published biostratigraphic data (Ryseth et al., 2002) revealing an excellent match between the two datasets, with: the top of S5a being coincident with the top Seledian, the top S5b broadly equating to the top Thanetian and the base of S5g corresponding to the regional, Intra Lutetian biostratigraphic timeline (Fig. 2). Furthermore, the top of sequences S3 and S4 equate to the top Early Cretaceous and top Late Cretaceous, respectively, whilst the top of Sequence S5 corresponds to the top Late Eocene (Fig. 2).

The study shows chemostratigraphy is a reliable tool for correlating the Tertiary and Cretaceous sequences encountered within the Western Barents Sea area. Furthermore, the technique can be used to revise the existing lithostratigraphic and biostratigraphic correlations for this area, despite variations in lithology, facies and depositional environment. This highlights the potential of chemostratigraphy as a standard tool for the correlation of these successions. In addition to providing a chemostratigraphic correlation, the geochemical data and selected mineralogical data are used to model changes in provenance, palaeoenvironment and facies.

Figure 1. Study map (left) showing the wells included in the Pilot study with their relative locations and the stratigraphy (right) applied to the study successions.

Figure 2. Chemostratigraphic and biostratigraphic integration.

 

 

AAPG Search and Discovery Article #90130©2011 3P Arctic, The Polar Petroleum Potential Conference & Exhibition, Halifax, Nova Scotia, Canada, 30 August-2 September, 2011.