using elemental geochemistry to improve sandstone reservoir characterization
TRANSCRIPT
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USING ELEMENTAL GEOCHEMISTRY TO IMPROVE SANDSTONE RESERVOIR
CHARACTERIZATION:A CASE STUDY FROM THE UNAYZAH A INTERVAL OF SAUDI ARABIA
Presenter:Abdullah [email protected]
Authors :MacDonald, Hardman, Sprague, Meridji, Mudjiono,
Galford, J., ... & Kelton. (2011)
Feb. 15, 2015
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Outline• Geological Background• Dataset• Results• Discussion• Summary
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Geological Background- Unayzah FM.
• The Unayzah Formation is an assemblage of mid-Carboniferous to Early Permian continental clastics deposited on the widespread “Hercynian” unconformity surface.
• Lower Unayzah is Glacio-fluvial (predominantly sandstones) to glacio-lacustrine (predominantly siltstones).
• Upper Unayzah is Fluvio-eolian and sabkha/wet interdune sandstones and siltstones with several significant intraformational unconformities.
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Geological Background- Paleozoic Stratigraphy
(Afifi, 2005)
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Geological Background- Dune field- U.A
(Al-Anazi, 2007)
The yellow area shows the location of known Unayzah A dune fields.
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Objectives• To provide a mineralogical and elemental compositional
baseline for the Unayzah A reservoir using an integrated core and log characterizations.
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Dataset - Mineralogical analysis, 60-ft section of core: Mineralogical Analysis: X-ray diffraction analysis (XRD). Elemental Analysis: Inductively-coupled plasma spectroscopy (ICP) and X-ray fluorescence spectroscopy.
- Data validation:* Wireline neutron-induced capture gamma-ray spectroscopy, GEM™.
* Halliburton Wireline tools:Capable of measuring ten formation elements run over the same interval.
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Results and Discussion
(MacDonald et al., 2011)
Sandstone: medium- to coarse, inclined planar laminations, rounded, well-sorted, (bimodal), Eolian dune deposits. Anhydrite nodules up to 15 cm in diameter.
Sandstone/Siltstone : very fine to fined, horizontal planar, wavy laminations, minor ripples, Eolian sand sheet and wet interdune deposits.
Eolian with thin interbedded sand sheets
Core Description:
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Results and Discussion
(MacDonald et al., 2011)
• Quartz grains and minor quartz overgrowth cement: 72-98 wt%.• Nodular anhydrite cement : 0-31 wt%.• Pore-filling kaolinite: 1-4 wt%.
Mineral Composition:
• Quartz grains and minor quartz overgrowth cement: 76-94 wt%• Nodular anhydrite cement : 0-22 wt%.• Highly crystalline kaolinite (diagenetic origin): 2-19 wt%.• Feldspars, illite, carbonate cement, and anatase : <1 wt%.
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Results and DiscussionElemental relationships and mineralogy
Unayzah A Mineralogical Components
QuartzE1:
Grains with minor cement
KaoliniteE2:
inferred diagenetic pore-fillings
AnhydriteE3:
Late nodular burial cement
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Results and DiscussionElemental relationships and mineralogy- Ternary plots
(MacDonald et al., 2011)
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Results and DiscussionElemental relationships and mineralogy- Principal Component Analysis
(MacDonald et al., 2011)
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Results and Discussion
(MacDonald et al., 2011)
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Results and Discussion
(MacDonald et al., 2011)
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Results and Discussion
(MacDonald et al., 2011)
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Results and Discussion
(MacDonald et al., 2011)
ICP XRDWireline Geochemical Log
Volumetric Analysis
Porosity
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Resu
lts a
nd
Dis
cuss
ion
(MacDonald et al., 2011)
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Summary• Core-to- log comparisons in heterogeneous formations can be
challenging and the results can be dependent on the core material sampling protocol.
• It is necessary to resort to sampling methods aimed at placing core derived elemental concentrations and mineralogy on a scale comparable to logs.
• Logs will tend to provide a better representation of the reservoir when large scale heterogeneity exists such as in the Unayzah A formation.
• Corrections is an important step in the workflow to obtain the best formation mineral evaluation from logs.
• Environmental effects on neutron logs can have an impact on porosity and mineralogy.
• Ternary plots of elemental data can be a used to identify or confirm the presence of various minerals. They can be especially useful in cases where XRD data from core samples are not available.
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