یافته‌های نوین زمین‌شناسی کاربردی

یافته‌های نوین زمین‌شناسی کاربردی

ارزیابی پتانسیل هیدروکربن­ زایی شیل ­های توربیدیتی سازند امیران در یک برش سطح­ الارضی از تاقدیس پشت­ جنگل، جنوب لرستان با استفاده از روش پیرولیز Rock–Eval 6

نویسندگان
1 دانش‌آموخته دکترا زمین‌شناسی، دانشکده علوم، دانشگاه لرستان، خرم‌آباد، ایران
2 دانشیار گروه زمین‌شناسی، دانشکده علوم، دانشگاه لرستان، خرم‌آباد، ایران
چکیده
سازند امیران (ماستریشتین پالئوسن) در حوضه­ رسوبی زاگرس با ضخامت قابل­توجهی در یک محیط رسوبی ژرف انباشته­ شده است، که از شمال لرستان به سمت جنوب، رخساره­های ریزدانه (تناوب شیل و ماسه­سنگ) غالب می­باشند. در این پژوهش، سازند امیران به‌عنوان سنگ منشأ احتمالی از دیدگاه زمین‌شیمی آلی و پتانسیل هیدروکربن­زایی در این بخش از حوضه­ رسوبی زاگرس مورد ارزیابی قرار گرفته است. در این راستا، یک برش چینه­شناسی سطح­الارضی به ضخامت 473 متر در یال شمالی تاقدیس پشت­جنگل، شهرستان کوهدشت، انتخاب و تعداد 20 نمونه از شیل­های تیره رنگ این سازند جهت آنالیز راکایوال 6 برداشت گردید. رسم مقادیر S2 در برابر TOC نمونه­ها، بیانگر یک سنگ منشأ ضعیف تا متوسط می­باشد و از نظر توان هیدروکربن­زایی، ضعیف ارزیابی می‌شود؛ به‌گونه­ای که شاخص سنگ منشأ (SPIr) این سازند 65/1 بوده و توان هیدروکربن­زایی ضعیفی دارد. کروژن این سازند مخلوطی از نوع III و نوع II تشخیص داده شد، اما کروژن نوع III فراوانی بیشتری دارد که می­تواند به دلیل چیرگی رخساره­های قاره­ای تشکیل دهنده این سازند باشد. رسم مقادیر Tmax در برابر HI نشان داد 75 درصد از نمونه­ها در محدوده نابالغ قرار گرفته و 25 درصد از آن­ها در ابتدای پنجره نفت­زایی قرار دارند؛ به عبارت دیگر، با رسیدن به مرحله کاتاژنز، بلوغ حرارتی را پشت سر گذاشته­اند که با Tmax بین 435 تا 460 درجه سانتی­گراد تأیید می­شوند. نمودار HI در مقابل TOC حاکی از تشکیل رخساره­های آلی گوناگون در سازند امیران می­باشد. این رخساره­ها شامل رخساره آلی CD (اکسیدان) 40 درصد، رخساره آلی C (نیمه اکسیدان) 45 درصد و به مقدار کمتر رخساره آلی BC (نیمه احیا تا نیمه اکسیدان) 15 درصد می­باشند. این تنوع رخساره­ای می­تواند به دلیل تنوع مواد آلی با منشأ دریایی و قاره­ای و رسوب­گذاری در محیط­های ژرف و بخش­های بالایی شیب قاره باشد، که منشأ قاره­ای آن­ها غالب می‌باشد. مقادیر TOC این سازند به دلیل ورود مواد آلی از منشأ قاره­ای پایین می­باشد (80 درصد نمونه­ها دارای TOC کمتر از 1 درصد وزنی می­باشند)، و لذا پتانسیل سنگ منشأ را کاهش داده است.
کلیدواژه‌ها

عنوان مقاله English

Evaluation of hydrocarbon generation potential of turbidite shales of Amiran Formation in a surface-terrestrial section of Pusht-Jangal anticline, south of Lorestan using pyrolysis Rock-Eval 6

نویسندگان English

Nasim Malekisadeghi 1
Ahmad Ahmadikhalaj 2
1 Ph.D. (graduated), Dept. of Geology, Faculty of Science, Lorestan University, Khorramabad, Iran
2 Assoc. Prof., Dept. of Geology, Faculty of Science, Lorestan University, Khorramabad, Iran
چکیده English

The Amiran Formation (Maastrichtian-Paleocene) in the Zagros sedimentary basin has been accumulated with a considerable thickness in a deep sedimentary environment, where from the north of Lorestan to the south, fine-grained facies (alternation of shale and sandstone) are dominant. In this research, the Amiran Formation was evaluated as a possible source rock from the point of view of organic geochemistry and hydrocarbon generation potential in this part of the Zagros sedimentary basin. In this goal, a 473-meter-thick stratigraphic section was selected on the northern side of the Pusht-Jangal anticline, Kohdasht city, and 20 samples of dark-colored shales of this formation were collected for Rock-Eval 6 analysis. Plotting the S2 values ​​against the Toc of the samples indicates a weak to medium source rock and it ranks weak in terms of hydrocarbon generating power, so that the source rock index (SPIr) of this formation is 1.65 and it has a weak hydrocarbon generating power. The kerogen of this formation was found to be a combination of type III and type II, but type III kerogen is more abundant, which can be due to the dominance of continental facies that make up this formation. Plotting the Tmax values ​​against HI showed that 75% of the samples are in the immature range and 25% of them are at the beginning of the oil generation window, or in other words, they have passed the thermal maturity by reaching the catagenesis stage, which is confirmed by Tmax between 435 and 460 degrees Celsius. The diagram of HI versus Toc indicates the formation of various organic facies in Amiran Formation, these facies include organic facies CD (oxidizing) 40%, organic facies C (semi-oxidant) 45% and to a lesser extent organic facies BC (semi-reduction to semi-oxidant) 15%. This variety of facies can be due to the variety of organic materials with marine and continental origin and sedimentation in deep environments and the upper parts of the continental slope, whose continental origin is predominant. The Toc values ​​of this formation are low due to the introduction of organic materials of continental origin (80% of the samples have Toc less than 1% by weight) and therefore the potential of the source rock has decreased.

کلیدواژه‌ها English

Amiran Formation
Hydrocarbon generation potential
Posht- Jangal anticline
Lorestan
Kohdasht
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  • تاریخ دریافت 21 فروردین 1404
  • تاریخ بازنگری 13 خرداد 1404
  • تاریخ پذیرش 18 خرداد 1404