ژئوشیمی قیرهای طبیعی باختر استان کرمانشاه (گیلان‌غرب)

جعفری, پویا; معانی جو, محمد; محسنی, حسن

doi:10.22084/psj.2024.29739.1448

ژئوشیمی قیرهای طبیعی باختر استان کرمانشاه (گیلان‌غرب)

نویسندگان

¹ دانشجوی کارشناسی‌ارشد زمین‌شناسی اقتصادی، گروه زمین‌شناسی، دانشکده علوم‌پایه، دانشگاه بوعلی‌سینا، همدان، ایران

² استاد گروه زمین‌شناسی، دانشکده علوم‌پایه، دانشگاه بوعلی‌سینا، همدان، ایران

10.22084/psj.2024.29739.1448

چکیده

ذخایر قیر طبیعی منطقه گیلان‌غرب، از دیدگاه زمینساختی در کمربند چین‌خورده زاگرس قرار گرفته است. ناحیۀ موردمطالعه در محدوده پهنه‌های زمین‌ساخت - چینه‌ای لرستان و میان‌رودان واقع شده است و به لحاظ ساختمانی در پهنۀ چین‌خوردة ساده قرار می‌گیرد. از روش آنالیز عنصری انجام شده بر روی نمونه‌های قیر طبیعی برای ارزیابی کیفیت قیرهای منطقه گیلان‌غرب، مشخص‌کردن نوع کروژن و میزان انعکاس تقریبی ویترینایت استفاده شد. بدین منظور تعداد هشت نمونه از ذخایر قیر طبیعی منطقه مورد بررسی ژئوشیمی آلی قرار گرفت. قیرهای ‌طبیعی استحصال شده از مخزن به طور معمول نسبت H/C کمتر از 1 دارند. کمترین میزان نسبت H/C، نمونه‌های مورد بررسی 15/1 است. باتوجه‌به این نکته، قیرهای طبیعی منطقه موردمطالعه مستقیماً از سنگ (‌های) مولد زایش یافته‌اند. میانگین کربن نمونه‌ها حدود 65 درصد است و قیرهای منطقه کیفیت بالایی دارند. قیرهای منطقه موردمطالعه عبارت‌اند از: گراهامیت (Ptm3)، آلبرتیت هوازده (Mjm, Ptm1)، گلانس‌پیچ (Jv, Ptm2) و گیلسونایت با هوازدگی کم (Jv). بین درصد خاکستر و درصد مواد فرار نمونه‌های قیر طبیعی و همچنین بین درصد خاکستر نمونه‌ها با درصد عنصر کربن رابطه معکوس وجود دارد و با افزایش میزان خاکستر، میزان کربن کاهش پیدا کرده و کیفیت قیر طبیعی کاهش پیدا می‌کند. رابطه مستقیمی بین درصد مواد فرار و میزان کربن نمونه‌ها وجود دارد و میزان مواد فرار به‌عنوان یک شاخص از کیفیت قیر طبیعی تلقی می‌گردد. بدین معنی که با افزایش آن کیفیت قیر طبیعی (میزان کربن) افزایش می‌یابد. بین میزان خاکستر و میزان عنصر هیدروژن در نمونه‌های قیر طبیعی رابطه عکس وجود دارد. بین درصد مواد فرار نمونه‌های قیر طبیعی با میزان عنصر اکسیژن رابطه عکس وجود دارد. اما بین درصد خاکستر نمونه‌ها با درصد عنصر اکسیژن رابطه مستقیم وجود دارد. رابطه مستقیم بین درصد مواد فرار و میزان هیدروژن نمونه‌ها برقرار است. تمامی نمونه‌ها وزن مخصوص بالاتر از یک و درجه ‌ API منفی دارند.

کلیدواژه‌ها

عنوان مقاله [English]

Geochemistry of natural bitumens in West of Kermanshah province (Gilan-e-Gharb)

نویسندگان [English]

P. Jafari ¹
M. Maanijou ²
H. Mohseni ²

¹ M. Sc. in Economic Geology, Dept., of Geology, Faculty of Sciences, Bu Ali Sina University, Hamedan, Iran

² Prof., Dept., of Geology, Faculty of Sciences, Bu Ali Sina University, Hamedan, Iran

چکیده [English]

The natural bitumen reserves in the Gilan-e-Gharb region are located in the Zagros Folded belt. The study area lies within the tectonic-stratigraphic zones of Lorestan and the Mesopotamia region, and structurally, within the simple fold belt. Elemental analysis conducted on natural bitumen samples was utilized to determine the types of bitumen in the Gilan-e-Gharb region, identify the various type of kerogen, and estimate the approximate reflectance of vitrinite. For these purposes, 8 samples from natural bitumen reserves were subjected to organic geochemical analysis. Natural bitumens with a reservoir origin typically have an H/C ratio of less than 1. Whereas, the analyzed samples have an average ratio of 1.15. Based on this data, the reservoir origin of the natural bitumens in the study area is deemed improbable.Hence a source rock origin for these reserves is plausible. The average carbon content of the samples is approximately 65 Wt%, indicating their high quality. The types of bitumen in the study area include Grahamite (Ptm3), weathered Albertite (Mjm, Ptm1), Glance Pitch (Jv, Ptm2), and low-weathered Gilsonite (Jv). An inverse relationship exists between the percentage of ash and the percentage of volatiles in the natural bitumen samples, as well as between the percentage of ash and the percentage of carbon. As the amount of ash increases, the carbon content decreases, leading to a reduction in the quality of the natural bitumen. A direct relationship is observed between the percentage of volatiles and the carbon content. This means that an increase in volatiles corresponds to an improvement in the quality of natural bitumen (and their carbon content as well). There is an inverse relationship between the carbon content and ash content and hydrogen value. Additionally, an inverse relationship exists between the percentage of volatiles and the oxygen content, while a direct relationship is notable between the percentage of ash and the oxygen content of the samples. A direct relationship is also established between the percentage of volatiles and the hydrogen content of the samples. All samples exhibit a specific gravity greater than one and a negative API degree which is probable due to relatively high sulfur and nitrogen content.

کلیدواژه‌ها [English]

Natural bitumen
Surface Evidence
Organic geochemistry
Ash content
Volatiles matter
Type of kerogen

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