Sheet voids and radiaxial fibrous calcite cement fills from Upper Jurassic beachrock, Calcaires Blancs de Provence, southeast France

1995 ◽  
Vol 10 (2) ◽  
pp. 252-260 ◽  
Author(s):  
A. F. Gray ◽  
A. E. Adams
Keyword(s):  
Upper Jurassic ◽  
Calcite Cement

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

Geosciences ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 446
Author(s):  
Dinfa Vincent Barshep ◽  
Richard Henry Worden
Keyword(s):  
Carbon Capture ◽  
Carbon Capture And Storage ◽  
Upper Jurassic ◽  
Reservoir Quality ◽  
Main Process ◽  
Shallow Marine ◽  
Porosity And Permeability ◽  
Calcite Cement ◽  
Diagenetic Evolution

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.

The case of the missing clay, aluminium loss and secondary porosity, South Brae Oilfield, North Sea

Clay Minerals ◽  
1994 ◽  
Vol 29 (4) ◽  
pp. 651-663 ◽  
Author(s):  
Ó. M. McLaughlin ◽  
R. S. Haszeldine ◽  
A. E. Fallick ◽  
G. Rogers
Keyword(s):  
Organic Acids ◽  
North Sea ◽  
Upper Jurassic ◽  
Local Source ◽  
Acid Solutions ◽  
The South ◽  
Submarine Fan ◽  
Secondary Porosity ◽  
Calcite Cement ◽  
Clay Formation

AbstractUpper Jurassic sandstones of the South Brae Field were deposited as a submarine fan complex. The earliest formed concretionary ferroan calcite cement passively encloses detrital feldspars which originally formed more than 10% of the rock. Later non-ferroan calcite at the concretion margins was precipitated from a more aggressive fluid. This fluid dissolved up to half of the feldspars and micas originally present, but little or no clay was precipitated. Aluminium must have been lost from the system.A late dissolution event has enhanced porosity by up to 8%. Feldspar was again reduced in volume by about half, leaving only ∼2% in the rock today. Very minor amounts of fibrous illite and kaolinite (<1%) form the last diagenetic cement. Aluminium must have again been lost from the system.As the Kimmeridge Clay Formation (KCF) encloses and interdigitates with the South Brae sandstones, a local source of organic acids is quite possible. These acid solutions may have increased the mobility of Al. The Al from the feldspars must have therefore been transported vertically into the KCF, or more probably transported laterally by compactional flows out of the basin (up to 10 km) during release of overpressured basinal water.

scholarly journals Diagenesis of Upper Jurassic sandstones of the Blokelv-1 core in the Jameson Land Basin, East Greenland

2018 ◽  
pp. 65-84
Author(s):  
Mette Olivarius ◽  
Rikke Weibel ◽  
Niels H. Schovsbo ◽  
Dan Olsen ◽  
Claus Kjøller
Keyword(s):  
Upper Jurassic ◽  
Late Eocene ◽  
Petrographic Analysis ◽  
Burial Depth ◽  
Early Eocene ◽  
X Ray Diffraction ◽  
X Ray ◽  
Lower Porosity ◽  
Porosity And Permeability ◽  
Calcite Cement

Petrographic analysis combined with X-ray diffraction are used to identify the diagenetic changes that have affected the porosity and permeability of gravity-flow sandstones of the Oxfordian–Volgian Hareelv Formation in the cored Blokelv-1 borehole in Jameson Land. Kaolinite replacement of albite grains probably occurred early after deposition and microquartz coatings formed under shallow burial. At deeper burial, illite and quartz formed from kaolinite and K-feldspar. Pervasive ankerite cement formed in the finest grained sandstones and may have formed at the expense of early calcite cement. Quartz overgrowths are volumetrically small, partly due to inhibition by microquartz coatings and partly due to limited residence time during deep burial. The succession reached the maximum burial depth of c. 2.8 km during the late Eocene. Basaltic material was intruded into the sediments during the early Eocene and the enhanced heat flow accelerated diagenesis in the close vicinity of the intrusions, which have thicknesses of up to 2 m. Most of the sandstones have porosities between 14.4 and 25.7% and permeabilities between 0.4 and 411.9 mD; this variation resulted from a combination of microquartz coatings and clay minerals. However, the intrusion-influenced sandstones and the ankerite-cemented sandstones have lower porosity and permeability.

Mineral composition and gemological characteristics of the fossil marine reptiles of the Ulyanovsk region

2018 ◽  
pp. 12-16 ◽  
Author(s):  
D. A. Petrochenkov
Keyword(s):  
Chemical Composition ◽  
Bone Tissue ◽  
Mineral Composition ◽  
Bone Structure ◽  
Upper Jurassic ◽  
Marine Reptiles ◽  
Ulyanovsk Region ◽  
Impurity Elements ◽  
Wide Assortment

Fossils of marine reptiles are a new jewelry and ornamental material and collected in the Ulyanovsk region from the Upper Jurassic deposits. They consist of (wt. %): calcite — 52, apatite — 24 and pyrite — 23, and also gypsum presents. The contents of radioactive and carcinogenic elements are close to background. The original bone structure of reptiles is preserved. Apatite replaces the bone tissue of marine reptiles, forming a cellular framework. According to the chemical composition, apatite refers to fluorohydroxyapatite with an increased Sr content. The size of the crystals is finely-dispersed. Calcite and pyrite fill the central parts of the cells. Calcite crystals of isometric and elongated shape, 0,01—0,05 mm in size, form blocks up to 0,3 mm during intergrowth. Calcite fills thin, discontinuous veins along the contour of cells with a width of up to 0,03 mm. In calcite, among the impurity elements, there are (wt. %, on the average): Mg — 0,30, Mn — 0,39 and Fe — 0,96. Pyrite forms a dispersed impregnation in calcite and apatite, content of impurities is, wt. %: Ni — up to 0,96 and Cu — up to 0,24. On technological and decorative characteristics of fossils of sea reptiles of Ulyanovsk region are qualitative jewelry and ornamental materials of biomineral group, allowing to make a wide assortment of jewelry and souvenir products.

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