Ankerite Cementation in Deeply Buried Jurassic Sandstone Reservoirs of the Central North Sea

Hendry, James P.; Wilkinson, Mark; Fallick, Anthony E.; Haszeldine, R. Stuart

doi:10.1306/2dc4090d-0e47-11d7-8643000102c1865d

Cited by 72 publications

(68 citation statements)

References 67 publications

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“…3B). Secondly, although ankerite syntaxially overgrows dolomite throughout the Franklin sandstones, there is a paragenetic break between dolomite and ankerite that represents more than 3000 m of burial (Hendry et al, 2000). During this interval, there is both minor dissolution of the dolomite as well as the onset of quartz overgrowth cementation.…”

Section: Isotopic Resultsmentioning

confidence: 99%

“…Dolomite±ankerite boundaries are invariably sharp in both CL and BSEM, but some compositional variation is present within the ankerite ( Fig. 3; Hendry et al, 2000).…”

Section: Dolomite Petrographymentioning

confidence: 98%

“…Molluscs would have been the dominant bioclasts in an Upper Jurassic shelf setting, so calcitic shell fragments would inevitably have accompanied the less stable aragonite and Mg-calcite detritus in the sediment. This calcite subsequently acted as the principal carbonate source for the ankerite (Hendry et al, 2000). The presence of silt-grade bioclastic material throughout the sandstone would simply have arisen from the decay of the organic matrix in the shells, followed by disaggregation and dispersal during bioturbation (cf.…”

Section: Origin Of Irregular Crystal Habitsmentioning

confidence: 99%

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Disseminated ‘jigsaw piece’ dolomite in Upper Jurassic shelf sandstones, Central North Sea: an example of cement growth during bioturbation?

et al. 2000

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Unusual textural and chemical characteristics of disseminated dolomite inUpper Jurassic shelf sediments of the North Sea have provided the basis for a proposed new interpretation of early diagenetic dolomite authigenesis in highly bioturbated marine sandstones. The dolomite is present throughout the Franklin Sandstone Formation of the Franklin and Elgin Fields as discrete, non-ferroan, generally unzoned, subhedral to highly anhedral`jigsaw piece' crystals. These are of a similar size to the detrital silicate grains and typically account for »5% of the rock volume. The dolomite crystals are never seen to form polycrystalline aggregates or concretions, or ever to envelop the adjacent silicate grains. They are uniformly dispersed throughout the sandstones, irrespective of detrital grain size or clay content. Dolomite authigenesis predated all the other signi®cant diagenetic events visible in thin section. The dolomite is overgrown by late diagenetic ankerite, and bulk samples display stable isotope compositions that lie on a mixing trend between these components. Extrapolation of this trend suggests that the dolomite has nearmarine d18 O values and low, positive d 13C values. The unusual textural and chemical characteristics of this dolomite can all be reconciled if it formed in the near-surface zone of active bioturbation. Sea water provided a plentiful reservoir of Mg and a pore¯uid of regionally consistent d 18 O. Labile bioclastic debris (e.g. aragonite, Mg-calcite) supplied isotopically positive carbon to the pore¯uids during shallow-burial dissolution. Such dissolution took place in response to the ambient`calcite sea' conditions, but may have been catalysed by organic matter oxidation reactions. Bioturbation not only ensured that the dissolving carbonate was dispersed throughout the sandstones, but also prohibited coalescence of the dolomite crystals and consequent cementation of the grain framework. Continued exchange of Mg 2+ and Ca 2+ with the seawater reservoir maintained a suf®cient Mg/Ca ratio for dolomite (rather than calcite) to form. Irregular crystal shapes resulted from dissolution, of both the dolomite and the enclosed ®ne calcitic shell debris, before ankerite precipitation during deep-burial diagenesis.

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Section: Isotopic Resultsmentioning

confidence: 99%

“…Dolomite±ankerite boundaries are invariably sharp in both CL and BSEM, but some compositional variation is present within the ankerite ( Fig. 3; Hendry et al, 2000).…”

Section: Dolomite Petrographymentioning

confidence: 98%

Section: Origin Of Irregular Crystal Habitsmentioning

confidence: 99%

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Disseminated ‘jigsaw piece’ dolomite in Upper Jurassic shelf sandstones, Central North Sea: an example of cement growth during bioturbation?

et al. 2000

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“…Chowdhury and Noble, 1996), and replaces biotite ( Figure 5(h)), calcite and dolomite ( Figure 5(d)). Comparable descriptions of precursor calcite and dolomite cements replaced by ankerite cements have been reported elsewhere (Hendry et al, 2000;Kantorowicz, 1985).…”

Section: Types Of Carbonate Cementsmentioning

confidence: 56%

“…Based on BSE imaging, dolomite is commonly zoned and replaced by ankerite ( Figure 5(d)). Hendry et al, 2000;Kantorowicz, 1985). Ankerite normally fills grain fractures and feldspar dissolution pores ( Figure 5(i), cf.…”

Section: Types Of Carbonate Cementsmentioning

confidence: 99%

Origin of carbonate cements with implications for petroleum reservoir in Eocene sandstones, northern Dongying depression, Bohai Bay basin, China

Cao

Wang

et al. 2016

Energy Exploration & Exploitation

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The Eocene Es4s interval is an important petroleum reservoir of sublacustrine fan dominated at the depths of 2500-4000 m in Dongying depression, Bohai Bay basin. Based on core observation, three types of carbonate-cemented beds have been identified and commonly contain ferroan calcite and ankerite predominantly and less calcite and dolomite. Precipitation temperatures range from 34.6 to 72.8 C for calcite and dolomite cements, and from 110 to 153 C for ferroan calcite and ankerite cements. The high 13 C PDB values (À0.65 to +5.59%) for calcite and dolomite suggest that dissolved inorganic carbon, derived from methanogenic fermentation of organic matter in adjacent mudstones. The low 13 C PDB values (+1.04 to +3.29%) for ferroan calcite and ankerite probably indicate a mixture of carbon derived from decarboxylation of organic acid as well as from the dissolution of early formed carbonate cements. High plug porosity is mainly developed at the central section of sandstones vertically and the porosity decreases sharply toward the top and base of the sandstones due to extensively carbonate-cemented beds. The carbonate-cemented beds varies from 0.02 to 0.5 m in thickness and might extend from tens to hundreds meters laterally. It could be served as fluid-flow barriers and seals for petroleum, and result in reservoir deterioration and significant heterogeneity.

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Linking Diagenesis and Porosity Preservation Versus Destruction to Sequence Stratigraphy of Gas Condensate Reservoir Sandstones; The Jauf Formation (Lower to Middle Devonian), Eastern Saudi Arabia

Al‐Ramadan¹,

Morad

Norton

et al. 2013

Linking Diagenesis to Sequence Stratigraphy

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Ankerite Cementation in Deeply Buried Jurassic Sandstone Reservoirs of the Central North Sea

Cited by 72 publications

References 67 publications

Disseminated ‘jigsaw piece’ dolomite in Upper Jurassic shelf sandstones, Central North Sea: an example of cement growth during bioturbation?

Disseminated ‘jigsaw piece’ dolomite in Upper Jurassic shelf sandstones, Central North Sea: an example of cement growth during bioturbation?

Origin of carbonate cements with implications for petroleum reservoir in Eocene sandstones, northern Dongying depression, Bohai Bay basin, China

Linking Diagenesis and Porosity Preservation Versus Destruction to Sequence Stratigraphy of Gas Condensate Reservoir Sandstones; The Jauf Formation (Lower to Middle Devonian), Eastern Saudi Arabia

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