using elemental geochemistry to improve sandstone reservoir characterization

-181 Advanced Stratigraphy-Geol 531-142

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


Outline• Geological Background• Dataset• Results• Discussion• Summary


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.


Geological Background- Paleozoic Stratigraphy

(Afifi, 2005)


Geological Background- Dune field- U.A

(Al-Anazi, 2007)

The yellow area shows the location of known Unayzah A dune fields.


Objectives• To provide a mineralogical and elemental compositional

baseline for the Unayzah A reservoir using an integrated core and log characterizations.


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.


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:




• 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%.


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


Results and DiscussionElemental relationships and mineralogy- Ternary plots



Results and DiscussionElemental relationships and mineralogy- Principal Component Analysis





ICP XRDWireline Geochemical Log

Volumetric Analysis

Porosity


Resu

lts a

nd

Dis

cuss

ion



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.

using elemental geochemistry to improve sandstone reservoir characterization

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