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Quantitative XRD bulk and clay mineralogical determination of paleosol sections of Unayzah and Basal Khuff clastics in Saudi Arabia

Published online by Cambridge University Press:  15 June 2012

Shouwen Shen ,
Syed R. Zaidi ,
Bader A. Mutairi ,
Ahmed A. Shehry ,
Husin Sitepu ,
Saud A. Hamoud ,
Fahad S. Khaldi  and
Fatimah A. Edhaim
Shouwen Shen*
Affiliation:
Research and Development Center, Saudi Aramco, Dhahran 31311, Saudi Arabia
Syed R. Zaidi
Affiliation:
Research and Development Center, Saudi Aramco, Dhahran 31311, Saudi Arabia
Bader A. Mutairi
Affiliation:
EXPEC Advanced Research Center, Saudi Aramco, Dhahran 31311, Saudi Arabia
Ahmed A. Shehry
Affiliation:
Research and Development Center, Saudi Aramco, Dhahran 31311, Saudi Arabia
Husin Sitepu
Affiliation:
Research and Development Center, Saudi Aramco, Dhahran 31311, Saudi Arabia
Saud A. Hamoud
Affiliation:
Research and Development Center, Saudi Aramco, Dhahran 31311, Saudi Arabia
Fahad S. Khaldi
Affiliation:
Research and Development Center, Saudi Aramco, Dhahran 31311, Saudi Arabia
Fatimah A. Edhaim
Affiliation:
Research and Development Center, Saudi Aramco, Dhahran 31311, Saudi Arabia
*
a)Author to whom correspondence should be addressed. Electronic mail: shouwen.shen@aramco.com
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Abstract

Quantitative X-ray diffraction (XRD) analysis is performed on 172 samples mainly containing paleosol sections of Unayzah and Basal Khuff clastics taken from the core of one well drilled by Saudi Aramco. Quantitative XRD bulk mineralogical determination is achieved using the Rietveld refinement method whereas quantitative XRD clay mineralogical determination of clay-size fraction is obtained using the reference intensity ratio method. The XRD results indicate that the samples from paleosol sections consist mainly of quartz and feldspar (microcline and albite) as framework constituents. Cement minerals include dolomite, hematite, anhydrite, siderite, gypsum, calcite, and pyrite. Clay minerals are important constituents in paleosols. The XRD results show that clay minerals in the samples are illite, mixed-layer illite/smectite, kaolinite, and chlorite. No discrete smectite is present in the samples. The clay mineral associations in these samples of paleosol sections can be classified into three types: Type I predominantly consists of illite and a mixed layer of illite/smectite; Type II of kaolinite; and Type III of illite and a mixed layer of illite/smectite, but also significant amounts of kaolinite. The change of clay mineral association type with sample depth can indicate the change of paleoclimate and paleoenvironment. For example, kaolinite usually forms under strongly leaching conditions such as abundant rainfall, good drainage, and acid waters. Therefore, XRD mineralogical data of paleosol sections are important for petroleum geologists to study paleoclimate and paleoenvironment and to predict the reservoir quality of the associated rock formations.

Keywords

quantitative XRD analysispaleosolclay-size fractionRietveld refinementreference intensity ratio
Type
Technical Articles
Information
Powder Diffraction , Volume 27 , Issue 2 , June 2012 , pp. 126 - 130
Copyright
Copyright © International Centre for Diffraction Data 2012

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