Mineralogy and Organic Petrology of Oil Shales in the Sangkarewang Formation, Ombilin Basin, West Sumatra, Indonesia
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Mineralogy and Organic Petrology of Oil Shales in The Sangkarewang Formation, Ombilin Basin, West Sumatra, Indonesia Fatimah Student no: 3008511 SCHOOL OF BIOLOGICAL EARTH AND ENVIRONMENTAL SCIENCES UNIVERSITY OF NEW SOUTH WALES 2009 ABSTRACT The Ombilin Basin, which lies in Sumatra Island, is one of the Tertiary basins in Indonesia. This basin contains a wide variety of rock units, from pre-Tertiary to Quaternary in age. Significant oil shale deposits occur in the Sangkarewang Formation which was deposited during Paleocene-Eocene time. Several analyses have been carried out namely, XRD, XRF, carbon and sulphur determination, thin section petrology, polished section petrology as well as Fischer assay. These were intended to determine the inorganic and organic constituents of the Sangkarewang oil shale. Inorganic constituents of the Sangkarewang oil shale consist mainly of quartz, feldspar, carbonates and a range of clay minerals, together in some cases with minor proportions of sulphides, evaporites and zeolites. The organic matter in the oil shales of the sequence is dominated by liptinite macerals, particularly alginite (mainly lamalginite) and sporinite. Cutinite also occurs in some samples, along with resinite and traces of bituminite. The dominance of lamalginite in the liptinite components suggests that the material can be described as a lamosite. Samples from the Sangkarewang Formation have vitrinite reflectance values ranging between 0.37% and 0.55%. These are markedly lower than the vitrinite reflectance for coal from the overlying Sawahlunto Formation (0.68%), possibly due to suppression associated with the abundant liptinite in the oil shales. Fischer assay data on outcrop samples indicate that the oil yield is related to the organic carbon content. Correlations with XRD data show that, with one exception, the oil yield and organic carbon can also be correlated directly to the abundance of carbonate (calcite) and inversely to the abundance of quartz plus feldspar. This suggests that the abundance of algal material in the lake sediments was preferentially associated with carbonate deposition. High yields of oil are noted in some samples, as a percentage of the organic carbon content. This may indicate that partial generation of hydrocarbons from the material has already taken place, in association with thermal maturation of the Sangkarewang succession. i CONTENTS Page Abstract i Contents ii List of Tables iv List of Figures v Chapter 1. Introduction 1 1.1. Definition of oil shale 1 1.1.1. Practical definition 1 1.1.2. Petrographic definition 2 1.2. Classification of oil shale 7 1.2.1. Mineralogical classification 8 1.2.2. Petrographic classification 9 1.3. Origin of oil shale 12 1.4. Depositional environment of oil shale 16 1.5. An example of an oil shale deposit 19 1.6. Indonesian oil shale deposits 19 1.7. Objectives of the present study 21 Chapter 2. Geological Setting of the Ombilin Basin 22 2.1. Regional setting 22 2.2. Tectonic setting 26 2.3. Stratigraphy 31 2.3.1. Pre-Tertiary rocks 35 2.3.2. Tertiary rocks 37 2.4. Depositional history 48 2.5. Previous work on Ombilin Basin oil shales 49 Chapter 3. Geology of the Talawi Area 53 3.1. Introduction 53 ii 3.2. Lithologic features 54 3.2.1. Pre-Tertiary rocks 55 3.2.2. Tertiary sedimentary rock units 57 3.2.3. Quaternary deposits 65 3.3. Stratigraphy 65 3.4. Structural geology 66 Chapter 4. Chemistry and Mineralogy of the Sangkarewang Oil Shale 67 Deposit 4.1. Chemical analysis 67 4.1.1. X-ray fluorescence analysis 69 4.1.2. Carbon and sulphur determination 75 4.2. Mineralogy 79 4.2.1. Background 79 4.2.2. XRD analysis techniques 83 4.2.3. Results 90 4.3. Evaluation of chemical and mineralogical data 92 4.3.1. Data from XRF analysis 92 4.3.2. Carbonate carbon and organic carbon 98 4.3.3. Comparison of XRD and XRF data 100 Chapter 5. Organic and Inorganic Petrology of the Sangkarewang Oil Shale 109 Deposit 5.1. Sedimentary petrography 109 5.1.1. Background 109 5.1.2. Analytical methods 111 5.1.3. Results 111 5.2. Organic petrology 114 5.2.1. Background 114 5.2.2. Analytical methods 116 5.2.3. Results 117 5.2.3.1. Organic constituents 117 iii 5.2.3.2. Vitrinite reflectance 121 Chapter 6. Oil Yield and Spent Shale Residues of the Sangkarewang Oil 125 Shale Deposit 6.1. Oil shale assays 125 6.1.1. Background 125 6.1.2. Analytical methods 126 6.1.3. Results 130 6.1.4. Relation of oil yield to other shale properties 130 6.2. Mineralogy of spent oil shale residues 134 Chapter 7. Conclusions 139 References 143 Acknowledgements 151 LISTOFTABLES Page Table 4.1. List of samples analysed 68 Table 4.2. Chemical composition of oil shales (Greensmith, 1978) 69 Table 4.3. Major element oxides from X-ray fluorescence analysis 73 Table 4.4. Minor elements from X-ray fluorescence analysis, expressed 74 as oxides Table 4.5. Results of sulphur and carbon analysis 77 Table 4.6. Sulphur obtained by calculation 78 Table 4.7. Classification of the clay minerals (Grim, 1953) 80 Table 4.8. Classification of phyllosilicates related to clay minerals 81 (Weaver, 1989, modified from Bailey, 1980b) Table 4.9. Classification of phyllosilicates with emphasis on clay 81 minerals (Moore and Reynolds, 1997) Table 4.10. Clay classification of Velde (1992) 82 Table 4.11. Siroquant results for typical oil shale sample (SR 15) 90 iv Table 4.12. Quantitative percentages of minerals identified in samples 91 studied using powder XRD and Siroquant Table 4.13. Calculation of oxide composition from mineral indicated by 101 Siroquant Table 4.14. Example of oxide composition calculation for SR 5 101 Table 5.1. Vitrinite reflectance for samples from the Sangkarewang 122 deposit Table 6.1. Example of modified Fischer assay spreadsheet 129 Table 6.2. Fischer assay data for samples from the Sangkarewang oil 130 shale deposit LISTOFFIGURES Page Figure 1.1. Van Krevelen diagram, showing the respective evolution path 4 of kerogen Figure 1.2. Maceral classification according to the subdivisions of the 5 Stopes-Herleen classification (Ward, 1984) Figure 1.3. Classification of sapropelites and sapropelic coals (Hutton et 10 al., 1980) Figure 1.4. Classification of organic-rich rocks (Hutton, 1987) 10 Figure 1.5. Secondary division of oil shales giving important properties of 13 each oil shale (Hutton, 1987) Figure 1.6. Important properties of oil shales and characteristics of 14 deposits (Hutton, 1987) Figure 2.1. Outline map of Sumatra, showing the location and extent of 23 the Ombilin Basin (de Smet, 1991). Figure 2.2. Geologic map of the Ombilin Basin (Koesoemadinata and 25 Matasak, 1981) v Figure 2.3. Idealised geologic cross section through the northern part of 27 the Ombilin Basin (Koesoemadinata and Matasak, 1981) Figure 2.4. Idealised geologic cross-section through the southern part of 28 the Ombilin Basin (Koesoemadinata and Matasak, 1981) Figure 2.5. Tectonic setting of Indonesia (Koesoemadinata and Matasak, 29 1981) Figure 2.6. Tectonic setting of Sumatra (Koesoemadinata and Matasak, 30 1981) Figure 2.7. Diagrammatic cross-section across Central Sumatra showing 33 the tectonic setting of the Ombilin Basin (Koesoemadinata and Matasak, 1981) Figure 2.8. Stratrigraphic sequence in the Ombilin Basin as defined by 34 different authors (de Smet, 1991) Figure 2.9. Vitrinite reflectance values and spore colour index profiles 43 from Sinamar No.1 (Koning, 1985) Figure 2.10. Stratigraphic units of the Ombilin Basin in the Sinamar No. 1 46 well (Koning, 1985) Figure 2.11. Typical saturate fraction gas chromatograms derived from 51 outcrop samples of the Sangkarewang Formation (Williams et al, 1995) Figure 3.1. Location map of the study area. 54 Figure 3.2. Thin section of granite from Padang Ganting (SR-43) 56 Figure 3.3. Thin section of granite from Ampang Nago (SR-42) 56 Figure 3.4. The Permian Silungkang Formation near Muara Kelaban 57 village Figure 3.5. Breccia of the Brani Formation exposed in the area north of 58 Sawahlunto town Figure 3.6. Thin section of Brani breccias in Sawahlunto town 59 Figure 3.7. Brani breccia with Sangkarewang shale fragment in 60 Malakutan River Figure 3.8. Outcrop of the Sangkarewang shale in Sawahlunto area, close 61 to the Sumpahan River vi Figure 3.9. Turbidite sandstone intercalated Sangkarewang shale in 61 Ampang Nago River Figure 4.1. A calibrated graph for K2O from the Philips PW 2400 72 calibration process Figure 4.2. Sample holder (“boat”) to be analysed by LECO CNS-2000 76 Figure 4.3. Sample on boat being inserted into LECO CNS-2000. 76 Figure 4.4. A powdered sample on an aluminium cavity sample holder in 84 the centre of XRD goniometer chamber Figure 4.5. Philips goniometer with the sample chamber on the centre 84 Figure 4.6. Preparation of oriented aggregates of clay fractions, showing 85 beakers for settling in the background and glass slides with clay concentrates in the foreground Figure 4.7. XRD pattern from SR 37 (powdered, glycolated and heated up 87 to 400oC) Figure 4.8. X-ray diffraction data from SR 15, showing the observed 89 diffractogram, the synthetic diffractogram obtained by Siroquant analysis, and the difference between them Figure 4.9. Correlation between SiO2 and loss on ignition (LOI) for 93 samples from the Sangkarewang Formation Figure 4.10. Correlation between CaO and SiO2 for samples from the 93 Sangkarewang Formation Figure 4.11. Correlation between CaO and LoI for samples from the 93 Sangkarewang Formation Figure 4.12.