پديد آورندگان :
رضايي، زينب نويسنده دانشجوي دكتري چينه‌شناسي و فسيل‌شناسي، دانشگاه آزاد اسلامي واحد علوم و تحقيقات تهران , , قاسمي‌نژاد، ابراهيم نويسنده استاد دانشكده زمين‌شناسي دانشگاه تهران , , حاجي‌كاظمي، الهام نويسنده دكتري رسوب‌شناسي و ژيوشيمي رسوبي، شركت نفت فلات قاره ايران , , شيخ ذكريايي ، سيد جمال نويسنده استاديار گروه زمين‌شناسي دانشگاه آزاد اسلامي واحد علوم و تحقيقات تهران ,
كليدواژه :
پيروليز راك- اول , پالينوفاسيس , سازند كژدمي , شواهد پالينولوژيكي
چكيده فارسي :
در طي اين مطالعه سعي شده است با بررسي شواهد فسيلي، رخساره‌هاي پالينولوژيكي و پيروليز راك- اول تغييرات شرايط محيطي و خصوصيات ژيوشيميايي سازند كژدمي در ميدان نفتي سروش تعيين گردد. براي اين منظور 124 نمونه مربوط به 147 متر مغزه براي مطالعات پالينولوژي و پالينوفاسيس آماده‌سازي و مطالعه گرديد. براين اساس چهار رخساره پالينولوژيكي (پالينوفاسيس‌هاي I, II, VI, IX) كه شاخص محيط‌هاي نزديك به ساحل هستند، تفكيك گرديد. اغلب جنس و گونه‌هاي شناسايي شده داراي بازه زماني طولاني هستند، با توجه به مطالعات صورت گرفته در ساير نقاط جهان و تطابق آنها با اطلاعات به دست آمده از نمونه‌هاي بررسي شده در اين مطالعه و ثبت ميكروفسيل‌هاي شاخص، سن سازند كژدمي در چاه SR-X آلبين در نظر گرفته شده است. همچنين با تعيين فاكتورهاي مختلف فسيل‌شناسي از قبيل نسبت‌هاي عناصر اصلي مواد آلي و پالينوفاسيس مربوط به هر نمونه و با تلفيق داده‌هاي به دست آمده، پنج سكانس رسوبي درجه سوم با مرزهاي سكانسي نوع دوم تعيين گرديد. علاوه براين نتايج حاصل از مطالعات پيروليز راك- اول نشان داد كه اين سازند در ميدان نفتي سروش از نظر پتانسيل توليد مناسب است و قادر به توليد هيدروكربن با كيفيت تجاري است. كروژن سازند كژدمي در ميدان مذكور عمدتاً نوع III كه توانايي توليد گاز را دارد. توزيع اطلاعات بر روي نمودارهاي مربوطه محدوده‌اي متغير را براي سازند كژدمي مشخص مي‌كند كه نشان از پسروي و پيشروي در طي انبايش اين سازند است كه حاكي از تغيير شرايط محيطي و شرايط نسبتاً اكسيدان در زمان نهشته شدن اين سازند است. اين نتايج به وسيله نمودار TOC در برابر S2 (به منظور تعيين نوع كروژن) كه نشان‌دهنده تركيب مواد آلي با منشا دريايي- خشكي (كروژنII/III ) است، تاييد مي‌شود كه نتايج به دست آمده از مطالعات پالينولوژيكي نمونه‌ها را تاييد مي‌نمايد.
چكيده لاتين :
Introduction
Many factors have been used for sea level analysis. A relatively new method is using palynological elements and factors such as biological degradation of palynological particles, roundness and homogeneity of equidimensional phytoclasts (Gorin & Steffen 1991), the relative abundance of opaque and semi opaque to transparent phytoclasts, the marine palynomorph/terrestrial particles ratio, relative abundance and diversity of dinoflagellate cysts and Chorate/Proximate, Proximochorate, Cavate (C/PPC) morphotype ratio (Ghasemi–Nejad et al. 1999). These factors were used for sequence differentiation in this paper. The aim of this study is to use palynofacies analysis and Rock-Eval pyrolysis to the investigate depositional environment and role of the Kazhdumi Formation as a hydrocarbon source in Soroosh oil field.
Method of study
Palynological preparation
One hundred and twenty four core samples from the well SR-X, were prepared in the palynology laboratory of the Department of Geology of Science and Research Branch, Islamic Azad University, Tehran. Standard preparation method of Traverse was used (Traverse, 2007). Cold hydrochloric (20%) and hydrofluoric (50%) acids were used to dissolve carbonates and silicates. No oxidants or alkalis were used. The residue was neutralized and centrifuged in ZnCl2 (specific gravity 1.9), then sieved at 20 mm using a nylon mesh and mounted on microscope slides using liquid Canada balsam. The microscope slides were examined with a Zeiss Axioscope microscope. Palynofacies analyses were also performed on these microscope slides. A total of 300 organic particles were counted and classified per sample and their proportions calculated.
Geochemical analysis
The Rock-Eval pyrolysis was carried out at Research Institute of Petroleum Industry, Tehran, Iran (RIPI). Twenty-two samples of mainly sandstone lithology were pyrolyzed for this purpose. The acquisition parameters S1 (free hydrocarbon), S2 (pyrolyzed hydrocarbon resulting from the decomposition of kerogen), S3 (expulsion of CO2), and Tmax (the temperature at which the S2 peak occurs) were measured. Rock-Eval analysis is a standard screening technique used for evaluating the source rock potential of a sedimentary rock (Laforgue et al., 1998) and consists a computer-controlled, temperature programmed pyrolysis oven and oxidation oven (Behar et al., 2001). An approximately, 100 mgr sample of pulverized whole rock was placed in the pyrolysis oven (which has a nitrogen atmosphere).
Conclusions
Four palynofacies types (I, II, VI, IX) have been recognized using the relative proportions of terrestrial elements, marine palynomorphs and amorphous organic matter (AOM). The study of samples has resulted in determination of 51 Genuses and 28 species of Dinoflagellates, 78 Genuses and 41 species of spores. According to studies on reported in other sides of the world and their comparison with the data obtained from the samples examined in this study and record the index microfossils, age of Kazhdumi Formation in Soroosh field have been determined Albian age. Based on the palynofacies and changes in percentages of the three major constituents of organic matter and correlation of all data, four fourth-order sequences were defined. The Kazhdumi Formation in the Soroosh Field is shown to be gas-prone, based on palynofacies analysis that identifies terrestrial phytoclasts (woody elements and leaf tissues) as a principal component, and Rock-Eval pyrolysis that shows the predominance of kerogen type III; it has entered into the oil window, therefore could have produced hydrocarbons. Also results of the optical analysis of kerogen for the Kazhdumi Formation show that vitrinite is the main maceral with a lesser amounts of liptinite and inertinite confirming kerogen type III as the main organic matter. The results obtained from optical analysis were used for comparison with those gained from Rock-Eval pyrolysis and palynofacies. In addition, in plotting HI versus OI values, most of the samples fall in C to CD restricts which indicate predominantly gas prone nature of the organic matter and shows depositional in a deltaic oxic environment with moderate to rapid rate. These environmental conditions is in consistency with data distribution in Dean et al. (1986). On the basis of this diagram, the Kazhdumi Formation shows a regressive trend in general.
Keywords: Palynofacies, Palynological evidences, Kazhdumi Formation, Rock-Eval pyrolysis.
