Estuarine clay mineral distribution: Modern analogue for ancient sandstone reservoir quality prediction

Abstract

The spatial distribution of clay minerals in sandstones, which may both enhance or degrade reservoir quality, is poorly understood. To address this, clay mineral distribution patterns and host‐sediment properties (grain size, sorting, clay fraction abundance and bioturbation intensity) have, for the first time, been determined and mapped at an unprecedentedly high‐resolution in a modern estuarine setting (Ravenglass Estuary, UK). Results show that the estuary sediment is dominated by illite with subordinate chlorite and kaolinite, although the rivers supply sediment with less illite and significantly more chlorite than found in the estuary. Fluvial‐supplied sediment has been locally diluted by sediment derived from glaciogenic drift deposits on the margins of the estuary. Detailed clay mineral maps and statistical analyses reveal that the estuary has a heterogeneous distribution of illite, chlorite and kaolinite. Chlorite is relatively most abundant on the northern foreshore and backshore and is concentrated in coarse‐grained inner estuary dunes and tidal bars. Illite is relatively most abundant (as well as being most crystalline and most Fe–Mg‐rich) in fine‐grained inner estuary and central basin mud and mixed flats. Kaolinite has the highest abundance in fluvial sediment and is relatively homogenous in tidally‐influenced environments. Clay mineral distribution patterns in the Ravenglass Estuary have been strongly influenced by sediment supply (residence time) and subsequently modified by hydrodynamic processes. There is no relationship between macro‐faunal bioturbation intensity and the abundance of chlorite, illite or kaolinite. Based on this modern‐analogue study, outer estuarine sediments are likely to be heavily quartz cemented in deeply‐buried (burial temperatures exceeding 80 to 100°C) sandstone reservoirs due to a paucity of clay grade material (<0·5%) to form complete grain coats. In contrast, chlorite‐enriched tidal bars and dunes in the inner estuary, with their well‐developed detrital clay coats, are likely to have quartz cement inhibiting authigenic clay coats in deeply‐buried sandstones.

Experimental study of chlorite authigenesis and influence on porosity maintenance in sandstones

“…Studies of the distribution of precursor clay coatings and chlorite in modern sedimentary environments have revealed that it is imperative to define specific sub-environments of deposition to fully understand and predict chlorite grain coats in ancient and deeply buried sandstones (Wooldridge et al 2017;Griffiths et al 2018;Griffiths et al 2019a;Griffiths et al 2019b;Virolle et al 2019;Virolle et al 2020). Temperature plays a key role in the rate of authigenic-chlorite precipitation in sandstones.…”

Stratigraphy and sedimentary evolution of a modern macro‐tidal incised valley: An analogue for reservoir facies and architecture

“…1629361412) data repository were also plotted on the palaeo-topographical map. The map further incorporates glacial till outcrop locality information from Ravenglass (Griffiths et al, 2019). Based on the 28 spot depths to glacial till, a tentative palaeo-topographical map of the Ravenglass area has been drafted, prior to the valley being infilled (Fig.…”

“…It is one of the most natural and least developed estuaries in the UK, with little industry and virtually no artificial coastal defences. The estuary lies on relatively flat low‐lying coastal plain, occupying an area of 5.6 km 2 , of which approximately 80% is intertidal (Bousher, 1999; Lloyd et al ., 2013; Wooldridge et al ., 2017a; Griffiths et al ., 2018, 2019; Wooldridge et al ., 2018). The estuary is a mixed energy, macrotidal system with a mean spring tidal range of >7 m, leaving the estuary nearly fully drained at low tide.…”

“…Data from cores published by Merritt & Auton (2000) and a core from the British Geological Survey (BGS, 1939, http://mapapps2.bgs.ac.uk/geoindex/home.html?layer=BGSBoreholes_ga=2.138148784.1233529240.1629361412-464657529.1629361412) data repository were also plotted on the palaeo‐topographical map. The map further incorporates glacial till outcrop locality information from Ravenglass (Griffiths et al ., 2019). Based on the 28 spot depths to glacial till, a tentative palaeo‐topographical map of the Ravenglass area has been drafted, prior to the valley being infilled (Fig.…”

Geology and taphonomy of a unique tyrannosaurid bonebed from the upper Campanian Kaiparowits Formation of southern Utah: implications for tyrannosaurid gregariousness

“…Analysis of clay inside a RUQ tyrannosaur centra shows it to have the same kaolinite fraction, but slightly higher chlorite and lower illite levels than either unit 3 or the unit 4 green and gray clasts ( Table S1 ). Seemingly, the constant kaolinite fraction and elevated chlorite and illite levels link all these clays genetically, with observed variations paralleling those in modern depositional settings with heterogeneous source areas ( Griffiths et al, 2019 ). Regardless, the contrasting infill of intact elements demonstrates their primary depositional context was not units 4 and 5, but a pedogenic mudstone similar to unit 3.…”