Identifying and Quantifying Thin Bedded Pay (Part A): Log Characteristics and Reservoir Quality

Distal intervals of interbedded sandstones and mudstones in shallow-marine, wave-dominated shoreface and deltaic reservoirs may contain significant hydrocarbon resources, but their reservoir properties are difficult to predict. Relatively small-scale (200 m x 100 m x 20 m), three-dimensional object-based reservoir models conditioned to outcrop analogue data have been used to investigate the controls on the proportion of sandstone, the proportion of sandstone beds that are connected by sandstone-filled erosional scours, and the effective vertical-to-horizontal permeability ratio (kv/kh) of such intervals. The proportion of sandstone is controlled by sandstone-bed and mudstone-interbed thickness, and by parameters that describe the geometry, dimensions and lateral-stacking density of sandstone-filled scours. Sandstone-bed connectivity is controlled by the interplay between the thickness of mudstone interbeds and sandstone-filled erosional scours. Effective kv/kh is controlled by the proportion of sandstone, which represents the effects of variable distributions and dimensions of mudstones produced by scour erosion, provided that scour thickness is greater than mudstoneinterbed thickness. These modelling results provide a means to estimate effective kv/kh at the scale of typical reservoir-model grid cells using values of mudstone-interbed thickness and proportion of sandstone that can potentially be provided by core data.

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

Onyenanu¹,

Hampson²,

Fitch³

et al. 2019

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The reservoir properties of distal lower shoreface and distal wave-dominated delta-front deposits, which consist of sandstone beds with locally scoured bases and mudstone interbeds, are poorly understood. The lower Rannoch Formation (Middle Jurassic Brent Group) forms an interval of such heterolithic sandstones in many North Sea reservoirs, and is used to illustrate a workflow for rapid estimation of reservoir properties and their sensitivity to key parameters. Mudstone-interbed thickness distributions in cored reservoir successions are compared to the thickness distribution of sandstone scour-fills in an outcrop analogue(s) in order to identify mudstones with the potential to form laterally extensive barriers to vertical flow. Effective kv/kh at the scale of several typical reservoirmodel grid cells (200 x 100 x 20 m) is estimated in intervals bounded by these mudstone barriers via a simple analytical technique that is calibrated to previously documented reservoir-modelling experiments, using values of sandstone proportion measured in cored reservoir successions. Using data from the G2 parasequence (Grassy Member, Blackhawk Formation, east-central Utah, USA) outcrop analogue, mudstones bounding 3-8 m thick, upward-coarsening successions in the lower Rannoch Formation may define separate stratigraphic compartments in which grid-cell-scale effective kv/kh is estimated to be 0.0001-0.001 using a streamline-based analytical method.

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Identifying and Quantifying Thin Bedded Pay (Part A): Log Characteristics and Reservoir Quality

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Identification and petrophysical evaluation of thinly bedded low-resistivity pay reservoir in the Niger Delta

Identification and petrophysical evaluation of thinly bedded low-resistivity pay reservoir in the Niger Delta

Effects of erosional scours on reservoir properties of heterolithic, distal lower-shoreface sandstones

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

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