Petrophysical evaluation and geochemical evidences for recognition of original carbonat mineralogy of Ilam Formation in the Asaluyeh cross section and South Pars Gas Field

Document Type : مقالات پژوهشی

Authors

• nazila shirooye nasab ¹
• roghayeh fallah bagtash ²
• mohammad hosein adabi ²
• mir reza mousavi ²

¹ shahidbeheshti of tehran

² shahidbeheshti university

10.22067/sed.facies.v10i1.53093

Abstract

Introduction
In this research, we tried to study the Ilam Formation using petrography (thin sections) and geochemical analysis (major and trace elements). Petrophysical studies have also been used to identify the characteristics and diagenetic environment, and to determine the sedimentary environment and evaluation of reservoir quality.
 
Materials and Methods
500 thin sections prepared from cutting samples in X and Y wells and 80 thin sections from Asaluyeh  section have been studied to identify, evaluate facies and type of sedimentary environment beside diagenetic processes of The Dalan Formation. For classification and texture descriptions, the classification schemes of Dunham (1962) used. The method of Dickson (1965) used to differentiate calcite from dolomite, with Alizarin (Red-S) and potassium Ferosianid. Types of dolomites were identifies (Adabi, 2009). For description of the microfacies and interpretation of depositional environment model, Flügel (2010) scheme was used. Study of Petrophysical Properties of Ilam Formation in the South Pars Gasfield have been done based on petrophysical logs (gamma, sonics and acoustic), geological reports and reservoir data.
 
Discussion and Conclusions
Major and trace elements analysis and especially their diagenesis are the important part of carbonates studies. According to the major and trace elements studies and the ratio of these elements in the limestone samples of Ilam Formation, the original aragonite mineralogy in shallow parts and original calcite mineralogy in deeper parts of these deposits were interpreted. Comparison of the Ilam limestone samples with ranges that presented to aragonitic limestone of other fields and plotting the samples in this area confirmed the mixed aragonite-calcite mineralogy. High contents of Sr and Na, low Mn content and high Sr/Na ratio for aragonitic samples and low Sr/Na ratio for calcite samples show that the limestone samples have been stabilized by fluids in a closed to open diagenetic system. The shale zones are almost similar in both wells, and the shale volume has peaked at the lower boundary of both wells due to the high percentage of shale in the Lafan Formation. The sharp changes in the upper and lower limits of the Ilam Formation represents a change in the boundary of this formation with upper and lower formations.
 
Keywords: Original carbonate mineralogy; gheochemistry; reservoir quality; Ilam Formation.
 
Reference
Adabi, M.H., & Asadi Mehmandosti, E., 2008. Microfacies and geochemistry of the Ilam Formation in the Tang-e- Rashid area, Izeh, S.W. Iran. Journal of Asian Earth Sciences, 33: 267-277.
Adabi, M.H., & Rao, C.P., 1991. Petrographic and geochemical evidence for original aragonitic mineralogy of Upper Jurassic carbonate (Mozduran Formation) Sarakhs area, Iran. Journal of Sedimentary Geology, 72: 253-267.
Bailey, T.K., Rosenthal, Y., McArthur, J.M., Van de Schootburge, B., & Thirlwall, M.F., 2003. Paleoceanographic changes of the late Pliensbachian-early Toarcian interval. a possible link to the genesis of Oceanic Anoxic Events. Earth Planatry Science Letter, 212: 307-32.
Bathurst, R.G.C., 1975. Carbonate Sediments and their Diagenesis. Developments in Sedimentology. Elsevier, Amsterdam, 658 p.
Brand, U., & Veizer, J., 1980. Chemical diagenesis of multicomponent carbonate system, II, stable isotopes. Journal of Sedimentary Petrology, 51: 987-997.
Brand, U., Azmy, K., & Veizer, J., 2006. Evaluation of the salinic I tectonic, Cancaniri glacial and Ireviken biotic events, Biochemostratigraphy of the Lower Silurian succession in the Niagara Gorge area. Canada and U.S.A. journal of Palaeogeography, Palaeoclimatology, Palaeoecology, 241: 192-213.
Budd, D.A., 1992. Dissolution of high-Mg calcite fossils and the formation of biomolds during mineralogical stabilization. Journal of Carbonates and Evaporites, 7: 74-81.
Cantrell, D.L., 2006. Cortical fabrics of Upper Jurassic ooid, Arab Formation, Saudi Arabia, Implication for original carbonate mineralogy. Journal of Sedimentary Geology, 186: 157-170.
Dresser Atlas, Log Interpretation Charts, Dresser Industries, Houston, TX (1979) 107 p.
Dickson, J.A.D., 1965. A modified staining technique for carbonate in thin section, Nature, v.205, 587 p.
Flugel, E., 2010. Microfacies of Carbonate Rocks. Springer-Verlag, Berlin, 1006 p.
Ghazban, F., 2007. Petroleum Geology of the Persian Gulf. Tehran University and National Iranian Oil Company, Tehran, 244-269.
Hood, S.D., Nelson, C.S., & Kamp, P.J.J., 2004. Discriminating cool-water from warm-water carbonates and their diagenetic environments using element geochemistry, the Oligocene Tikorangi Formation (Taranaki Basin) and the dolomite effect, New Zealand. Journal of Geology and Geophysics, 47: 857-869.
Khatibi Mehr, M., & Adabi, M.H., 2013. Microfacies and geochemical evidence for original aragonite mineralogy of a foraminifera-dominated carbonate ramp system in the late Paleocene to middle Eocene, Alborz basin, Iran. Journal of Carbonates and Evaporites, 146-163.

Keywords

• Original carbonate mineralogy
• gheochemistry
• reservoir quality
• Ilam Formation

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