ارزيابي ژيوشيميايي سازند پابده در ميدان نفتي نصرت واقع در جنوب شرق خليج فارس با استفاده از داده‏هاي حاصل از پيروليز راك ايول VI

Geochemical evaluation of Pabdeh Formation in Nosrat field, southeast Persian Gulf using Rock- Eval VI pyrolysis

مطالعه حاضر بر روي 59 نمونه از خرده هاي حفاري سازند پابده در ميدان نفتي نصرت، به وسيله دستگاه پيروليز راك ايول 6 صورت گرفته است. نتايج ژيوشيميايي بر اين امر دلالت مي‏كند كه سازند پابده داراي پتانسيل هيدروكربني ضعيف تا خوب مي‏باشد. ترسيم پارامتر S1 در مقابل TOC براي نمونه‏ها، عدم آلودگي آنها به نفت خام و مواد روغني (در حين حفاري) را تاييد مي‏كند. منحني تغيير رخساره آلي دياگرام جونز نشان‏دهنده محدوده B-BC براي سازند پابده بود كه بيانگر محيط‏هاي دريايي احيايي تا كمي اكسيدان مي‏باشد. رسم دياگرام HI در برابر Tmax نيز براي نمونه‏هاي مورد مطالعه نشان داد كه نوع كروژن نمونه‏ها تركيبي از انواع II-III كه تمايل بيشتر به كروژن نوع II (توانايي توليد نفت بيشتر) دارند و نشان‏دهنده ورود نمونه‏ها به پنجره نفتي است. همچنين، ترسيم نمودار تغييرات S1+S2 در برابر TOC نيز بيانگر اين است كه سازند پابده با داشتن محدوده وسيع از لحاظ پتانسيل توليد مي‏تواند به عنوان سازندي خوب براي توليد هيدروكربن در منطقه مورد مطالعه عمل نمايد.

Introduction: Organic geochemistry plays an important role in exploration of oil and gas. Nowadays, most oil companies strictly recommend use of organic geochemical maps in oil and gas exploration and do not intend to drill without having assessed geochemical data. In this study, Rock-Eval -VI was used in order to achieve geochemical data. In addition, in this study using standard geochemical data from Pabdeh Formation located in Nosrat oil field, SE Persian Gulf was investigated for evaluating petroleum potential. Material and Methods: In this study a total of 59 cuttings (Well#NH-01 and depth interval 1128 to 2547 meter) from Pabdeh Formation, Nosrat oil field were analyzed. Attempt was made to choose unweathered samples with chiefly shale and marl lithology. Each sample with 50 to 70 mg weight was powdered and homogenized before having subjected to Rock-Eval pyrolysis VI for the purpose of geochemical evaluation. Discussion: To ascertain sample under investigation are devoid of any possible staining or contamination S1 vs TOC cross plot was used. This suggests that all samples from Pabdeh Formation are insitu and not contaminated. In order to assess kerogen type and maturity, using HI vs OI plot (adapted from Van Krevlen plot; Alizadeh et al., 2012) indicated that samples from Pabdeh Formation have chiefly a mixture of kerogen type II and III and rarely kerogen type II. Organic matter maturity is generally assessed using Rock-Eval pyrolysis parameters such as Tmax and HI and using HI vs Tmax cross plot (Hunt, 1996). This cross plot for samples from Pabdeh Formation suggested that most samples have entered oil window however, samples are in the beginning of oil generation window. In other words, these samples are thermally at late diagenesis or early catagenesis stages. This again indicates that Pabdeh Formation having reached to early catagenesis ( Tmax > 435 ?C) is considered as a possible source rock and is in the early stages of thermal maturation. In order to evaluate hydrocarbon generative potential, geochemical parameters including HI and TOC were used (Abubakr et al., 2014). A cross plot of HI vs TOC shows that samples from Pabdeh Formation are plotted in poor to good region. Conclusions: Geochemical studies and interpreting Rock-Eval VI pyrolysis results on Pabdeh Formation (Well#NH01, Nosrat Oil field Persian Gulf), it can be concluded that based on HI and Tmax parameters most samples from Pabdeh Formation have entered oil window and are in the beginning of oil generation stage. In addition, most samples have chiefly a mixture kerogen type II and III. From the point of view of organic richness, Pabdeh Formation is considered to be poor to good and therefore is a possible source rock with intermittent hydrocarbon potential. All these suggest that Pabdeh Formation in the Nosrat oil field is considered as a candidate source rock and a detailed geochemical investigation including Gas Chromatography (GC) and gas Chromatography Mass Spectrometry (GCMS) is recommended. Keywords: Rock -Eval VI pyrolysis, Pabdeh Formation, Hydrocarbon Potential, Jones Diagram, Nosrat Oil Field.