Laminaset geometries in fine grained shallow marine sequences: core data from the Rannoch Formation (North Sea) and outcrop data from the Kennilworth Member (Utah, USA) and the Bencliff Grit (Dorset, UK)

Abstract

Sandbodies from storm‐dominated marine and marginal marine environments commonly contain intervals of laminated fine sandstones. A characteristic of such lamination is the presence of low angle cross lamination. In order to model correctly the effects of such lamination on a waterflood of an oil‐bearing shoreface sequence it was necessary to quantify the geometry of the laminaset elements. This challenge has been greatly complicated by the lack of outcrop of the formation of interest. The Middle Jurassic Rannoch Formation of the North Sea only occurs in the subsurface where it is not possible in core to measure the aspect ratio of laminasets directly. In this study, the laminaset geometry data that can be obtained from core (e.g. apparent set thicknesses) were collected for the Rannoch Formation. These data were compared with similar data from potential outcrop analogues in (1) the Cretaceous Kennilworth Member of the Blackhawk Formation in Utah, USA and (2) the Upper Jurassic Bencliff Grit from the Dorset coast, UK. A quantitative analysis of laminaset geometries has been used to compare subsurface core with potential outcrop analogues. The Rannoch Formation core is characterized by numerous low angle truncations. We have measured these features in two wells (means of 7.2° and 12.1°). Mean apparent set thicknesses were 0.24 and 0.19 m. In the outcrop sections studied, truncation angles ranged from 9.6° to 13.4° and mean set thicknesses from 0.24 to 0.34 m. Mean bounding surface dips of 5.8° and 8.6°, and mean laminaset lengths of 2.3 and 4.1 m were also measured. directly in the field and by using photomosaics. On the basis of this comparison, the Kennilworth Member in Utah was found to be the most suitable and the geometries (i.e. aspect ratios) measured there were used to generate an appropriate geometry of Rannoch laminaset geometries for use in engineering studies: laminaset length, 2.0 m; laminaset thickness, 0.2 m.

Sampling procedure for small-scale heterogeneities (crossbedding) for reservoir modelling

“…Examples of distributions are given in literature (Johnson, 1975;Corbett et al, 1994;Bridge, 1997). Width W and length L are estimated from values obtained at outcrops or from equations (HartkampBakker, 1993;Weber, 1987).…”

“…Values and distributions can be taken from literature (Corbett et al, 1994;Johnson, 1975;Storms, 1999) or from borehole imaging tools (Mercadier and Livera, 1993, Williams and Soek, 1993Knight, 2002).…”

Characterization of effective permeability in heterolithic, distal lower-shoreface sandstone reservoirs: Rannoch Formation, Brent Group, UK North Sea

“…6A) are interpreted as the expression in core of hummocky cross-stratification (e.g. Scott, 1992;Corbett et al, 1994), which is widely interpreted to record deposition from strong oscillatory or combined oscillatory and unidirectional flows set up by storm waves (e.g. Dott & Bourgeois, 1982;Arnott & Southard, 1990;Dumas & Arnott, 2006).…”

Sedimentary processes and provenance of Quaternary marine formations from the Tangier Peninsula (Northern Rif, Morocco)

“…These structures are sharply truncated by low-angle planar cross-bedding, formed by coarse-to medium-grained calcareous sandstone. Furthermore, fine-grained and well sorted heterolithic sediments with a parallel lamination and low-angle cross lamina-sets (sensu Corbett et al, 1994) are made up of a mixture of calcareous sand; calcilutites are also present. The grain-size of coarse-and fine-grained lithofacies ranges between À1 and 2u.…”