CHARACTERIZATION OF SOME NEW IRANIAN BITUMEN A. R. Mirhabibi + , B. Mehrabi*, A. E. Nazar Beigy ■ , M. Haghighi ■ , H. Norooz Zadeh ■ , A. Moini ■ , F. Alinia i and P. Padyav* + Iran University of Science and Technology *Tarbiat Moalem University ■ Research Institute of Petroleum Industry i Amir Kabir University of Technology Introduction The native asphalt or natural bitumen refers to a wide variety of natural materials, which contains varying amounts of bitumen as defined by solubility in carbon disulfide[1]. Native asphalt varies considerably in composition and properties. From a practical point, it may be convenient to classify the asphalt into three groups according to their bitumen content and other properties, which are shown in Table 1 [2]. It is claimed that the only commercially important deposits of gilsonite in the world are located in Unita Basin, in the northeast corner of Utah. However, other reports have shown that this material exist in other places such as: Venezuela. There are many natural bitumen deposits along the Zagross trend at NW Iran. These deposits mainly located at fracture zones and unconformities of the Tertiary sequence rocks. There are more than 100 localities, which theses natural bitumen outcropped at NW Iran and small scale mining has been in operation in some of them. Geological setting The natural bitumen deposits of Iran lies along the main Zagros fault with SE-NW direction. These deposits are found in Folded Zagros belt (Fig.1), which has 200-250 km width. The sedimentary sequences consist of shale, siltstone, sandstone, marl, limestone and evaporites from the Late Paleozoic to the Tertiary age which are formed at the east of Arabian platform margin. The natural bitumen deposits are mainly located at the Gachsaran and Amiran formations. Gachsaran formation consists of anhydrite with red and green shale and limestone laminations. This formation is a cap rock of many oil traps at the Zagros belt. Amiran formation consists of green to brown siltstone and sandstone [3]. There has been no systematic exploration program to evaluate these deposits. From geological point of view the main controls on natural bitumen deposits of Iran are stratigraphic and structural controls. In some places local folding or faulting in evaporites sequence resulted in emplacement of natural bitumen deposits (Fig 2). Blocks of evaporites are normally found in most of deposits (Fig3). Characterization The samples from five localities at the Kermanshah province were collected and used for chemical and physical characterization. The samples were studied by optical microscopy, X-ray diffraction and SEM techniques. The raw samples were heated under a reducing atmosphere and the texture of the samples were revealed before and after heating by an optical microscope and SEM. Impurities in as received samples were analyzed by EDS and XRF techniques. After burning of the samples the remained ashes were weighted and analyzed by XRF. The remainder of insoluble materials in CS 2 , toluene, and benzene were used for mineral identification by XRD. For studying the thermal behavior of the samples techniques such as, DTA, TG and TMA were applied. From ball and ring method was used for estimation of the softening point of the samples. The elemental analysis of C, N, H, and S, solubilities in CS 2 , benzene, ash content, specific gravity and their thermal characterization were determined at the Research Institute of Petroleum Industry (RIPI) labs. Results and Discussion From geological studies in this work it seems the origin of Iranian bitumens is gradual evaporation of crude oil, which is intruded into the rocks and fissures (Fig. 2). The quality of the bitumens is dependent to processes such as oxidation, sulfurization, polymerization and condensation which in turn affected by time (age), temperature and pressure. Various kinds
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CHARACTERIZATION OF SOME NEW IRANIAN BITUMEN
A. R. Mirhabibi+, B. Mehrabi*, A. E. Nazar Beigy■, M. Haghighi■, H. Norooz Zadeh■, A. Moini■, F. Aliniai and P. Padyav* +Iran University of Science and Technology
*Tarbiat Moalem University ■Research Institute of Petroleum Industry
iAmir Kabir University of Technology Introduction The native asphalt or natural bitumen refers to a wide variety of natural materials, which contains varying amounts of bitumen as defined by solubility in carbon disulfide[1]. Native asphalt varies considerably in composition and properties. From a practical point, it may be convenient to classify the asphalt into three groups according to their bitumen content and other properties, which are shown in Table 1 [2]. It is claimed that the only commercially important deposits of gilsonite in the world are located in Unita Basin, in the northeast corner of Utah. However, other reports have shown that this material exist in other places such as: Venezuela. There are many natural bitumen deposits along the Zagross trend at NW Iran. These deposits mainly located at fracture zones and unconformities of the Tertiary sequence rocks. There are more than 100 localities, which theses natural bitumen outcropped at NW Iran and small scale mining has been in operation in some of them. Geological setting The natural bitumen deposits of Iran lies along the main Zagros fault with SE-NW direction. These deposits are found in Folded Zagros belt (Fig.1), which has 200-250 km width. The sedimentary sequences consist of shale, siltstone, sandstone, marl, limestone and evaporites from the Late Paleozoic to the Tertiary age which are formed at the east of Arabian platform margin. The natural bitumen deposits are mainly located at the Gachsaran and Amiran formations. Gachsaran formation consists of anhydrite with red and green shale and limestone laminations. This formation is a cap rock of many oil traps at the Zagros belt. Amiran formation consists of green to brown siltstone and sandstone [3].
There has been no systematic exploration program to evaluate these deposits. From geological point of view the main controls on natural bitumen deposits of Iran are stratigraphic and structural controls. In some places local folding or faulting in evaporites sequence resulted in emplacement of natural bitumen deposits (Fig 2). Blocks of evaporites are normally found in most of deposits (Fig3). Characterization The samples from five localities at the Kermanshah province were collected and used for chemical and physical characterization. The samples were studied by optical microscopy, X-ray diffraction and SEM techniques. The raw samples were heated under a reducing atmosphere and the texture of the samples were revealed before and after heating by an optical microscope and SEM. Impurities in as received samples were analyzed by EDS and XRF techniques. After burning of the samples the remained ashes were weighted and analyzed by XRF. The remainder of insoluble materials in CS2 , toluene, and benzene were used for mineral identification by XRD. For studying the thermal behavior of the samples techniques such as, DTA, TG and TMA were applied. From ball and ring method was used for estimation of the softening point of the samples. The elemental analysis of C, N, H, and S, solubilities in CS2, benzene, ash content, specific gravity and their thermal characterization were determined at the Research Institute of Petroleum Industry (RIPI) labs. Results and Discussion From geological studies in this work it seems the origin of Iranian bitumens is gradual evaporation of crude oil, which is intruded into the rocks and fissures (Fig. 2). The quality of the bitumens is dependent to processes such as oxidation, sulfurization, polymerization and condensation which in turn affected by time (age), temperature and pressure. Various kinds
of bitumen have been investigated in this study. As a consequence of the above mentioned factors the following types were recognized: natural soft and liquid asphalt, hard asphalt, and asphaltic pyrobitumens. The high quality grades usually containing less than 10% inorganic solid materials mainly consist of clays, silicates, carbonates and sulfates. Table 2 shows typical analysis of the inorganic solid obtained from XRD and XRF analysis. The melting point of the high quality bitumen samples is around 150˚C. Penetration at 60˚C under 100 g. load in 5 sec. was ~0.1mm. Fig. 4, shows a typical TG graph of one of the samples under argon. Volatile materials at ~163˚C for 5h is less than 7wt.% and at ~204˚C for 5h is up to 20 wt.%. Solubility in CS2 is usually more than 90% and averages, C, H, N, S, contents are 82, 11, 2, and 2, wt.% respectively. The nitrogen content is much higher than petroleum oils in general and this can considered as an evidence of gilsonite. Typical properties of a high quality Iranian bitumen are shown in Table 3. Fracture surface of high quality natural bitumen is concoidal (Fig. 3R). This behavior of fracture again is one of the well known character of gilsonite. Conclusions Natural bitumen deposits of Iran located at the Zagros folded belt, with SE-NW direction. These deposits has outcropped in many localities and there has been no systematic exploration program for assessing the economic potentials of them. In recent studies the characterization of natural bitumen from Kermanshah province has revealed that gilisonite is one of the main constituents of Iran’s natural bitumen deposits. References: [1] Standard Definitions of Terms Relating to Materials for Roads and Pavements, ASTM D04.03, Philadelphia 1984, ASTM D. 8-83. [2] Ullmann’s Encyclopedia of Industrial Chemistry, Fifth Edn, Vol. A3. VCH, 1995. [3] James JA and Wynd JG. Stratigraphic Nomenclature of Iranian Oil Consortium Agreement Area. Am. Assoc. Pet. Geol. Bull., 1965; 49: 2182-2245.
[4] Alavi M. Tectonics of the Zagros orogenic belt of Iran: new data and interpretations. Tectonophysics 1994; 229: 211-283. Acknowledgments. The authors would like to thanks Iran Ministry of Oil for the financial support. Research sponsored by the Research Institute of Petroleum Industry.
Figure 2. Emplacement of natural bitumen in local fold, Kermanshah Province.
Table 1: Three classes of natural asphalts. Class Nearly pure bitumen Appreciable
mineral matter Small fraction of
bitumen Name Asphaltite Lake asphalt Rock asphalt Solubility in CS2 (%) 98 53 7 Softening point(ºC) 195 93 - Penetration at 25ºC 2 1 - Sp. Gr. 1.07 1.40 2.30 Examples Gilsonite USA &
Venezuela Trinidad Kentucky, USA &
France
Table 2: Typical elemental and mineralogical composition of Iran’s natural bitumen. Elements Minerals Major Trace Ca, S, Si Fe, V, Ti, Al, Cl, Mn, Ni, Mo, Sr Quartz, Calcite, Gypsum, Anhydrite,
Hematite
Table 3: Typical properties of Iran’s high grades natural bitumen. Sp. Gr. Softening
point (ºC) Solubility in
CS2 (%) Ash content
(%) Moisture
(%) Volatiles at
900 ºC Fixed
Carbon 1.18 160 95 6.00 1.30 72.20 20.50
Figure 1. Zagros subdivisions; 1 = Precambrian basement, 2 = Zagros thrust zone, 3 = Uremieh-Dokhtar assemblage (arc). Abbreviations: C. S. = Caspian Sea; D. = Dorud; E. = Esfahan; K. = Kerman; MZT = Main Zagros Thrust, P. G. = Persian Golf; Sh. = Shiraz; T. = Tehran; ZSFB. = Zagros Simply Folded Belt [4].
Figure 3. Intruding natural bitumen along fracture zones with remnant block of gypsum (Left) and concoidal fractures on natural bitumen. Figure 4. Leakage of liquid bitumen from bulk of solid bitumen after explotation. Figure 5. Therogravimetric analysis of a typical high quality bitumen from Kermanshah Province.
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