Post on 18-Jun-2020
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Thin section petrography
We offer three options, depending on the degree of information required:
Quicklook petrography: involves a brief description of the major detrital minerals and diagenetic phases. This is the least detailed option but facilitates rapid scanning of a number of thin sections to assess trends and variations. It is also applicable to poor quality thin sections, for instance from cuttings or sidewall core samples.
Detailed description: includes a description of framework grains, ductile phases, authigenic clays and cements with a visual abundance estimate. Pore type and distribution are assessed, and the main factors controlling reservoir quality are identified.
Detailed description with point count: This is the most detailed option. Detrital and authigenic phases, pore types etc are described as for the previous option, but in addition a 200 grain point count is performed to generate more reliable quantitative compositional data. This is the most common option for routine petrographic studies.
All thin sections are impregnated with blue-dyed araldite to identify porosity and are fully stained for K-feldspar and carbonate cements to aid mineral identification.
Examples of a petrographic data sheet and photomicrographs are shown below.
Petrographicservices
WELL: DEPTH: 3750.34m PLUG NO.: 14
DESCRIPTION: A general view of a well sorted, fine (lower) Facies 1 sandstone. There is a significant amount of open, moderately connected remnant primary porosity. Note also the relatively common, orange stained, uncorroded K-feldspar grains.
He Ø = 19.5% Kh = 273mD FIELD OF VIEW: 3.6mm
WELL: DEPTH: 3737.94m PLUG No.: 33 DESCRIPTION: This photo shows a mica-rich lamina within a very fine (upper) Facies 1 sandstone. The lamina is significantly more compacted than adjacent mica-poor areas and contains little or no remnant porosity. Fluid flow within the sand is therefore likely to be anisotropic. Note also the presence of a siltstone clast.
He Ø = 21.5% Kh = 88mD FIELD OF VIEW: 3.6mm
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WELL: PLUG NO: 33 He POROSITY: 30.4%
FORMATION: DEPTH: 6611.70ft PERMEABILITY: 2455mD
GRAIN SIZE: Fine (upper) COMPACTION: Mod low TOTAL FRAMEWORK: 92.5%
RANGE: StM - ML SHAPE: Subangular to subrounded TOTAL DUCTILE: 2.0%
SORTING: WS STRUCTURE: Grain size lamination TOTAL AUTHIGENIC: 5.5%
TOTAL MACROPOROSITY: 22.5%
FRAMEWORK GRAINS: 92.5%
Monocrystalline qtz 77.5% Dominantly strained metamorphic grains
Polycrystalline qtz 6.0% Strained metamorphic grains
Microcrystalline qtz 0.5% Chert and ?igneous grains
K-feldspar 4.5% Untwinned to locally lamellar twinned grains, little or no dissolution
Plagioclase 1.5% Scattered lamellar twinned grains showing minor dissolution
Lithics 1.0% Mainly ?phyllitic grains showing some dissoluion
Bioclasts 0.0%
Heavy minerals 1.5% Mainly sphene, with scattered opaque oxides, zircon, garnet and amphibole/pyroxene
Volcaniclasts 0.0%
Carbonate grains 0.0%
DUCTILE COMPONENTS 2.0%
Muscovite 0.5% Rare laths, slightly altered to kaolin
Biotite Tr% Rare relatively fresh laths
Chlorite 0.0%
Organic material 0.0%
Mudclasts 0.0%
Detrital clays 1.5% Minor poorly formed, rarely pore-filling clays
AUTHIGENIC CEMENTS 0.5%
Quartz overgrowth 0.5% Minor euhedral terminations
Microcrystalline quartz 0.0%
Calcite Tr% Minor slightly ferroan rhombic cement is probable calcite
Dolomite 0.0%
Siderite 0.0%
Haematite 0.0%
Barite 0.0%
Pyrite 0.0%
Hydrocarbon 0.0%
AUTHIGENIC CLAYS 5.0%
Illite/smectite 0.0%
Chlorite 0.0%
Kaolin 5.0% Interstitial, microporous pore-filling masses, rarely demonstrably formed from
muscovite
MACROPOROSITY 22.5%
Predominantly open, well connected primary porosity (22.5%) with trace amounts of secondary porosity in partly corroded feldspars and lithics
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