Three-Dimensional Reservoir Architecture of a Valley-Fell Sequence and a Deltaic Aggradational Sequence: Influences of Minor Relative Sea-Level Variations (Scalby Formation, England).
R. Eschard, C. Ravenne, P. Houel, R. Knox, 1991. "Three-Dimensional Reservoir Architecture of a Valley-Fell Sequence and a Deltaic Aggradational Sequence: Influences of Minor Relative Sea-Level Variations (Scalby Formation, England).", The Three-Dimensional Facies Architecture of Terrigenous Clastic Sediments and its Implications for Hydrocarbon Discovery and Recovery, Andrew D. Miall, Noel Tyler
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In the Middle Jurassic series of the Cleveland basin (Northeastern England), the Scalby Formation comprises two main members, interpreted as a valley-fill complex overlain by a deltaic aggradational series. The valley was incised during a relative sea-level drop and infilled during a stepped relative sea-level rise by a retrogradational fluvial to estuarine complex. The valley fill is composed of three superposed sandsheet prisms showing, respectively, 1. fluvially dominated straight channels, 2. tidally influenced meander belts, and 3. a mixed fluvial-tidal meander belt The deltaic aggradational member corresponds to highstand deposits. Small ribbons or meandering channels are isolated in shaly floodplain and lacustrine facies.
A precise three-dimensional reservoir reconstruction has been carried out on a 1-km2 area using cliff sections, drill cores, wireline logs and petrophysical measurements. Accurate reservoir reconstructions are presented here as large cross sections in terms of lithology, porosity and permeability. At Cloughton, the valley-fill member consists of a lower and upper prism. Each corresponds to a channel-fill stage with a basal aggradational fluvial unit overlain by an estuarine or paralic transgressive unit The basal prism displays a fluvial stacked-chaanel unit with side bars and sand or clay plugs, the tops of which are truncated by a transgressive surface. The unit is overlain by an estuarine sand-flat complex. The upper prism corresponds to tidally-influenced meander belts with hectometric point bars composed of argillaceous sandstone and siltstone. It is capped by shaly marsh deposits, corresponding to the period of maximum flooding of the valley fill. The aggradational deltaic member consists mainly of delta-plain shales with multistory ribbon channels and wide meander belts.
The best potential reservoirs are located in the basal fluvial sucked channels of the valley fill. Reservoir qualities decrease in the estuarine sand-flat complex and are very poor in the mixed fluvial-tidal meander belts. The small ribbon channels generally constitute good but small disconnected reservoirs. The sequence stratigraphy of the Scalby Formation shows that reservoir geometry and architecture could be controlled by minor relative sea-level variations.