Reservoir Quality of Upper Jurassic Corallian Sandstones, Weald Basin, UK

Abstract

The Upper Jurassic, shallow marine Corallian sandstones of the Weald Basin, UK, are significant onshore reservoirs due to their future potential for carbon capture and storage (CCS) and hydrogen storage. These reservoir rocks, buried to no deeper than 1700 m before uplift to 850 to 900 m at the present time, also provide an opportunity to study the pivotal role of shallow marine sandstone eodiagenesis. With little evidence of compaction, these rocks show low to moderate porosity for their relatively shallow burial depths. Their porosity ranges from 0.8 to 30% with an average of 12.6% and permeability range from 0.01 to 887 mD with an average of 31 mD. The Corallian sandstones of the Weald Basin are relatively poorly studied; consequently, there is a paucity of data on their reservoir quality which limits any ability to predict porosity and permeability away from wells. This study presents a potential first in the examination of diagenetic controls of reservoir quality of the Corallian sandstones, of the Weald Basin’s Palmers Wood and Bletchingley oil fields, using a combination of core analysis, sedimentary core logs, petrography, wireline analysis, SEM-EDS analysis and geochemical analysis to understand the extent of diagenetic evolution of the sandstones and its effects on reservoir quality. The analyses show a dominant quartz arenite lithology with minor feldspars, bioclasts, Fe-ooids and extra-basinal lithic grains. We conclude that little compactional porosity-loss occurred with cementation being the main process that caused porosity-loss. Early calcite cement, from neomorphism of contemporaneously deposited bioclasts, represents the majority of the early cement, which subsequently prevented mechanical compaction. Calcite cement is also interpreted to have formed during burial from decarboxylation-derived CO2 during source rock maturation. Other cements include the Fe-clay berthierine, apatite, pyrite, dolomite, siderite, quartz, illite and kaolinite. Reservoir quality in the Corallian sandstones show no significant depositional textural controls; it was reduced by dominant calcite cementation, locally preserved by berthierine grain coats that inhibited quartz cement and enhanced by detrital grain dissolution as well as cement dissolution. Reservoir quality in the Corallian sandstones can therefore be predicted by considering abundance of calcite cement from bioclasts, organically derived CO2 and Fe-clay coats.

Sedimentary Facies Controls for Reservoir Quality Prediction of Lower Shihezi Member-1 of the Hangjinqi Area, Ordos Basin

“…In China, unconventional tight gas provides the most contribution of the unconventional resources and accounts for 39.2% reserves and 24.6% annual production of the total natural gas [3]. Therefore, many geoscientists are working on the reservoir quality prediction of sandstone reservoirs [4][5][6][7]. The Ordos basin (OB) is one of the most productive basins with the highest annual gas output in China [8,9].…”

Hinterland environments of the Late Jurassic northern Weald Basin, England

“…this suggests an early diagenetic origin (Figures 6a, b, 7a) (Barshep & Worden, 2021. Calcite cement is present at different stages of neomorphism of primary bivalve shells (Figure 6b); the outline of the bivalve shells is locally preserved by micrite envelopes.…”

“…The SEM‐EDS instrument used in this study was an FEI WellSite QEMSCAN, at the University of Liverpool, using a tungsten‐filament, operating at 15 kV and equipped with two Bruker EDS detectors (Wooldridge et al, 2018). The technique makes use of a Scanning Electron Microscope (SEM) equipped with two or more high‐speed Energy Dispersive X‐Ray Spectroscopy (EDS) detectors (Armitage et al, 2011; Barshep & Worden, 2021; Worden & Utley, 2022; Worden, Utley et al, 2018) to give a quantitative proportion of mineral assemblages. In this study, the ideal minimum practical spacing resolution of 2 μm was used for higher resolution analyses and 20 μm spacing was used where average mineralogy across a whole polished section was required.…”

“…The two fields are relatively close to the London-Brabant Massif (15 km) (Figure 1). The Corallian (Oxfordian) sandstones are at shallow presentday depths (< 1000 m true vertical depth) and have not been buried deeper than about 1500 m, hence they are not significantly altered by mesodiagenesis (Barshep & Worden, 2021. The lack of burial diagenesis and relative proximity to the sediment source terrain make the…”

“…The two fields are relatively close to the London‐Brabant Massif (~15 km) (Figure 1). The Corallian (Oxfordian) sandstones are at shallow present‐day depths (< 1000 m true vertical depth) and have not been buried deeper than about 1500 m, hence they are not significantly altered by mesodiagenesis (Barshep & Worden, 2021, 2022). The lack of burial diagenesis and relative proximity to the sediment source terrain make the case study suitable for the reconstruction of the palaeogeology, palaeoclimate and palaeotectonic setting of the Jurassic LBM area, as well as for the investigation of the effects of sedimentological controls on provenance analysis.…”