Organo-mineralogical insights of shale gas reservoir of Ib-River Mand-Raigarh Basin, India

Accepted Manuscript Organo-mineralogical Insights of Shale Gas Reservoir of Ib-River Mand-Raigarh Basin, India Vinod Atmaram Mendhe, Susheel Kumar, Alka Damodhar Kamble, Subhashree Mishra, Atul Kumar Varma, Mollika Bannerjee, Vivek Kumar Mishra, Sadanand Sharma, John Buragohain, Balram Tiwari PII:

S1875-5100(18)30370-6

DOI:

10.1016/j.jngse.2018.08.026

Reference:

JNGSE 2698

To appear in:

Journal of Natural Gas Science and Engineering

Received Date: 15 April 2018 Revised Date:

17 July 2018

Accepted Date: 25 August 2018

Please cite this article as: Mendhe, V.A., Kumar, S., Kamble, A.D., Mishra, S., Varma, A.K., Bannerjee, M., Mishra, V.K., Sharma, S., Buragohain, J., Tiwari, B., Organo-mineralogical Insights of Shale Gas Reservoir of Ib-River Mand-Raigarh Basin, India, Journal of Natural Gas Science & Engineering (2018), doi: 10.1016/j.jngse.2018.08.026. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED Organo-mineralogical InsightsMANUSCRIPT of Shale Gas Reservoir of Ib-River Mand-Raigarh Basin, India Vinod Atmaram Mendhea, Susheel Kumarb, Alka Damodhar Kamblec, Subhashree Mishraa, Atul Kumar Varmab, Mollika Bannerjeea, Vivek Kumar Mishraa, Sadanand Sharmaa, John Buragohaina, Balram Tiwarib a

CSIR - Central Institute of Mining and Fuel Research, Dhanbad 826015 Dept. of Applied Geology, Indian Institute of Technology (ISM), Dhanbad 826004 c Dept. of Chemical Engineering, Indian Institute of Technology (ISM), Dhanbad 826004

E-mail: [email protected]

Abstract

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b

In the present study, Permian shale beds of Ib-River Mand-Raigarh Basin have been evaluated for insights of depositional conditions, organic, clay and mineral composition allied to

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shale matrix. The shale core samples were obtained during exploratory drilling and analysed for the properties like proximate, petrography, Rock-Eval, Total organic content (TOC), X-ray

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diffraction (XRD) and X-ray fluorescence (XRF). The values of vitrinite content and TOC varies from 2.00 - 16.20 (vol.%) and 1.88 - 6.99 wt. % with an average value of 10.34 (vol.%) and 3.75 (wt.%) respectively, suggesting fair to excellent source rock potential of shale for gas. Whereas, results of the Rock-Eval pyrolysis indicated fair to very good source rock potential (S1: 0.04 0.22 and S2: 0.57 - 39.45). The indicator of thermal maturity parameters like Tmax (423 - 470 ᵒC) and VRo (0.64 - 0.96 %), counsels moderately matured shales. The plot of hydrogen index (HI)

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vs oxygen index (OI), Tmax vs HI and TOC vs HI illustrated the presence of type II and III kerogen in studied shales. The uniformity in carbon conversion elucidates negligible effects of intrusive and basin tectonics on shale reservoir which is validated from the passive stable tectonic setting of Ib-River Mand-Raigarh basin which favours deposition of organic matter. The

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high percentage of quartz (26.30 - 57.60 vol.%) signifying the resistive nature of SiO2 towards erosion and weathering. However, the negligible or typical absence of K-feldspar and a large

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percentage of kaolinite (16.80 - 53.30 vol.%) attributed to the strong weathering process. Consequently, the instantaneous reduction condition supported the preservation and transformation of organic matter. The paper focuses on the significance of various essential parameters like depositional

conditions, organic richness, the degree of maturation, clay types and mineral constituents on the gas genesis and storage. The parameters interpreted through facies and evolution history of the basin to evaluate the prospects of shale gas resource development in Ib-River Mand-Raigarh Basin, India. Keywords: Organic; thermal maturity; mineralogical composition; depositional conditions; kerogen type.

ACCEPTED MANUSCRIPT 1. Introduction Recently, the organic rich shale deposits have emerged as the potential source of hydrocarbons (Mendhe et al., 2017a). The fine grained clastic sediments (mud and clay) were deposited under low oxygen environmental conditions (Mendhe et al., 2017a and b; Mishra et al., 2018a; Varma et al., 2018). Subsequently, the sinking of the basin due to an overload of sediments has favoured the preservation and transformation of organic matter with the increase

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in the depth of burial and thermal gradient (McKenzie, 1978; Mishra et al., 2016; Mendhe et al., 2016, 2017a). The substantial clay content (>65%) makes the shale bed intrinsically impermeable. However, the advancement in exploration, horizontal-multilateral drilling, hydrofrac and recovery technologies in past two decades supported to the enormous potential

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shale gas resource development in the world (Curtis, 2002; Jarvie et al., 2007; Pollastro, 2007; Ross and Bustin, 2009; Mendhe et al., 2017c). Usually, shale have complex mineralogy

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consisting of varieties of clay (kaolinite, Illite, chlorite, smectite and montmorillonite) and minerals (quartz, feldspar, muscovite, siderite, calcite, pyrite, dolomite etc.) which form a porous matrix for storage of methane gas (Jones et al., 1989; Lee and Sidle, 2010). Maceral content help to determine the significance of organic matter and their discrete pattern throughout the horizon of interest (Tissot and Welte, 1984; Vandenbroucke and Largeau, 2007). Additionally, organo-petrographic studies are being used to reconstruct the

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palaeoenvironmental condition of deposition which revolves the facies and evolution history of the basin (Mukhopadhyay and Gormly, 1984; Diessel, 1986; Kalkreuth et al. 1991; Jasper et al., 2010). Total organic carbon (TOC) and Rock-Eval pyrolysis parameters S1, S2, S3, HI, OI, PI and Tmax are used to estimate the organic richness, source rock potentiality, kerogen type and

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thermal maturation of shale beds (Espitaliè et al., 1977; Tissot and Welte, 1984; Peters, 1986; Varma et al., 2015). Similarly, vitrinite reflectance (VRO %), measured on vitrinite macerals in

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shale, is another valued parameter for assessing the thermal maturity which also reflects the depositional pattern of shale rock (Curtis et al., 2012). The mineralogical composition, TOC and kerogen type present in the shale rocks are

directly influenced by the intensity of weathering, transportation mechanisms, rate of sedimentation and post depositional processes (Nesbitt and Young, 1982, 1984; Bhatia, 1983; Roser and Korsch, 1988; McLennan et al., 1993; Nesbitt et al., 1996; Baioumy et al., 2016). The geochemical properties of shale reflect the genesis, weathering and post-depositional history of shale (Pettijohn, 1975; Graver and Scott, 1995). XRD and XRF are the valuable tools to identify and determine the quantitative mineral phases which have a distinct crystal structure. This paper discusses the influence of depositional conditions on organo-mineralogical constituents of shale

MANUSCRIPT in respect to gas genesis and ACCEPTED storage. This study shall help to evaluate critical facets of the shale reservoir for hydrocarbon resource development in Ib-River Mand-Raigarh Basin of India. 2.

Study Site- Ib-River Mand- Raigarh Basin The Ib-River Mand-Raigarh Basin occupies the central part of the upper Mahanadi valley

Gondawana belt and extend over a vast stretch lying between Ib valley in the east, Korba and Hasdo-Anand coalfield in the west lying within the Mahanadi grabens (Fox, 1931; Raja Rao,

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1983), bounded by latitude 21° 45' - 22° 42' and longitude 83° 01' - 83° 44' covering an area about 900 sq. Km. (Raja Rao, 1983; Coal Atlas of India, 1993; Dutt, 2003), in the Chhattisgarh state of India. The geological map of Ib-River Mand-Raigarh Basin marked with the location of investigated borehole samples is presented in Fig. 1. It displays a shallow synclinal structure,

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with axis trending in NW-SE direction and the prominent boundary fault demarcates the southern basin margin. In the central and southern part of the basin, the Barakar and Barren

sediments (Chakraborti et al., 2002).

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Measures has attained thick shale beds lie at a more considerable depth below the younger

The stratigraphic succession of Ib-River Mand-Raigarh Basin is dominated by Lower Gondwana sediments (lower Permian to middle Triassic) and classified into the rock of Talchir, Barakar, Barren Measures, Raniganj and Kamthi Formations, rest unconformably over the Precambrian crystalline basement (Chakraborti et al., 2002; Murthy et al., 2014). Talchir

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formation unconformably overlies the Barakar and Barren Measures mostly by arenaceous and argillaceous facies comprising predominantly of basal boulder bed, stratified tillite in thin beds associated with conglomerate, fine to medium grained interbedded sandstone, siltstone, coal seams and carbonaceous shale having thickness ranges 424.00 - 460.00 m deposited during

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Lower Permian to Upper Carboniferous time. Some basic dykes, sills and flows have been observed in the northern part of the basin (Casshyap and Tewari, 1988, Bose et al., 1992). The

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generalised lithostratigraphy of the Ib-River Mand-Raigarh Basin, Chhattisgarh (modified after Casshyap and Tewari, 1988; Chakraborti et al., 2002) is presented Fig. 2. 3.

Experimental

3.1. Shale core sampling, preparation and proximate analysis Altogether twenty (20) shale core samples were collected from Barakar Formation with the

laterally varying depth of 55.00 - 348.00 m, from four different boreholes namely BH-1, BH-2, BH-3 and BH-4 (Fig. 1 and Table 1). The samples were crushed and sieved to 212µm for proximate, Rock-Eval and TOC, XRD and XRF analysis as suggested by Bureau of Indian Standard (BIS, 2003). The petrographic pellets were made by crushing the sample in size <1 mm and fixed it using epoxy resin in a mould of size 25 mm diameter and 16 mm in height. The fixed pellets were air dried and polished using alumina grade I, II and III as per the procedure laid

ACCEPTED MANUSCRIPT down by International Committee of Organic Petrology (ICCP: 1971, 1973, 1998 and 2001). Standard laboratory procedure as set down by the Bureau of Indian Standard (BIS, 2003) was followed to carry out the proximate analysis. 3.2. TOC and Rock-Eval pyrolysis The Vinci Technologies Rock-Eval 6 system is used to determine TOC content and pyrolysis parameters following the procedure suggested by several researchers (Espitaliè et al.,

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1977; Tissot and Welte, 1984; Peters, 1986; Varma et al., 2015; Mishra et al., 2018b). The RockEval pyrolysis analysis was carried out at Keshava Deva Malaviya Institute of Petroleum Exploration (KDMIPE), Oil and Natural Gas Corporation Limited (ONGC), Dehradun, India. The hydrocarbons released by programmed heating of prepared samples in a stream of helium at

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300 oC for 5 min are recorded as the area under the first peak on the pyrogram (S1; mg HC/g rock), second peak on the pyrogram is composed of pyrolytic hydrocarbons generated by thermal breakdown of kerogen as the sample is heated from 300 to 600 oC (S2: mg HC/g rock) at 25

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o

C/min and CO2 generated by kerogen degradation is retained during the heating from 300 to 390

o

C and is analysed as the third peak (S3: mg CO2/g rock) (Mendhe et al., 2017a, b, c). During

pyrolysis and combustion, the released CO and CO2 are monitored online by means of an infrared cell. This complementary data acquisition is used to determine the TOC content. Moreover, Tmax is maturity parameter and corresponds to the temperature at which maximum

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amount of hydrocarbons are released from the thermal degradation of kerogen. The other pyrolysis indices are calculated like hydrogen index (HI) = 100 × S2/TOC, oxygen index (OI)= 100×S3/TOC and production index (PI)=S1/(S1+S2) (Espitaliè et al., 1977; Tissot and Welte,

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1984; Mendhe et al., 2017a, b, c).

3.3. Maceral and vitrinite reflectance The petrographic analyses were carried out using a “Carl Zeiss Axio Imager M2m”

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microscope under reflected white and fluorescence light in oil immersion lens following standard procedures as prescribed by ICCP (1971, 1998, 2001). More than 1000 maceral points were counted with the help of auto petrolouge stage covering the entire area of the pellet. The random vitrinite reflectance (VRo %) was measured on the collotelinite maceral in monochromatic light using 50x objectives in immersion oil (refractive index: 1.518) over approx 50 grains (Taylor et al., 1998; ICCP: 1998 and 2001; ISO-11760, 2005; ISO 7404-5, 2009). 3.4. X-ray diffraction (XRD) analysis XRD analysis was performed on crushed powdered (~212 µm) shale samples using Bruker XRD-diffractometer. The samples were mounted on a dry slide glass (zero diffraction plate) and placed in a sample holder. The X-ray diffractometer, equipped with Cu-Kα radiation measured

MANUSCRIPT on an incident angle at 0.5ᵒ.ACCEPTED Identified mineral constituents over a range of between 0 to 75o (2
), from their characteristic peak positions and intensities. Quantitative phase analyses were done to determine the relative volume percentage of minerals following the Reitveld method (Chalmers and Bustin, 2008; Ufer et al., 2008; Ji et al., 2017). 3.5. X-Ray fluorescence (XRF) analysis XRF analysis was performed on ash samples. The shale samples were analysed for ash

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content following the procedure suggested by the Bureau of Indian Standards (BIS, 2003). The ash sample pressed into moulds to prepare pellets. The Bruker make “S8 Tiger XRF machine”

Na2O, K2O and P2O5. 4.

Results and Discussion

4.1. Organic richness and depositional environment

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was used to determine the major oxides such as SiO2, TiO2, Al2O3, Fe2O3, Mn3O4, MgO, CaO,

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The studied shale core samples comprise light grey to dark grey colour, dull lustre, fracture mainly along the bedding planes, visible discrete and sub-angular quartz, flecks of mica along the laminae, altered grains of feldspar and irregular slickensides. The litho band by band analyses reveals alternate bands of clay-sericite, siltstone, intercalations, organic rich grey to dark grey carbonaceous shale bands and interbedded shaly siltstone with parallel laminae (Fig. 3). The extensive heterogeneity in litho-bands attributed to irregular sediments supply and

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organic matter due to variation in transport and depositional process under the low energyreducing environment (Mendhe et al., 2017e) (Table 1). Further, the carbonaceous and silty shale implies onshore several transition bedding

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characteristics under palaeosol-restricted limno-terrestrial-fluivial unidirectional currents (Jacob et al., 1958; Mendhe et al., 2017a, e). The abundance of clay (>65%) and the mineral grains of quartz, k-feldspar, mica, siderite, dolomite and carbonates specifying granitic source rock

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undergone through cyclic weathering, erosion and pre-post diagenetic process (Chandra, 1990 and 1992; Mendhe et al., 2017e and d). Proximate constituents like moisture, ash yield, volatile matter and fixed carbon varies from 1.00 - 4.32, 69.33 - 89.26, 7.16 - 17.16 and 0.42 - 11.58 wt.% (Table 1) respectively. The high ash yield reveals the high sediments input as a result of periodic flooding during deposition, because of change in river course in a shallow flood plain. Moreover, the variation in density of organic matter and inorganic content from a heterogeneous mixture, consequently subjected to low energy depositional conditions (Siavalas et al., 2009; Padhy and Das, 2013). TOC content of the studied shale samples ranges from 1.88 - 6.99 wt.% with average value of 3.75 wt.%; except for the coaly shale sample CG#1438, which has TOC value 21.34 wt.% (Table 2). It may be observed that dark carbonaceous shale contains higher TOC than lighter

ACCEPTED MANUSCRIPT colour shale, although some exceptions found due to heterogeneously distributed dark grey thinlaminae along the bedding plane. TOC content signifies fair to good source rock potential of shale beds for gas genesis (Varma et al., 2015; Mendhe et al., 2016 and 2017a; Mishra et al., 2018a). The excellent positive correlation of fixed carbon and TOC (R2=0.94) (Fig. 4a), suggests the ample amount of organic carbon in shale beds. Therefore, fixed carbon can be used to

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replicate the TOC content of shale beds in the study area. Fig. 4b, exhibits negative relationship of TOC and ash yield (R2=0.78), reflecting sediments cover and influx of surface water in an alternating oxic and anoxic depositional mires to fluvial systems controlled by sediment

2013; Raji et al., 2015; Mendhe et al., 2017a). 4.2. Evaluation of source rock potential

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transport, mixing, and alteration of silicate minerals during diagenesis process (Hakimi et al.,

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The results of Rock-Eval pyrolysis including values of S1, S2, S3, PI, HI, OI and Tmax are presented in Table 2. The low S1 values vary from 0.04 - 0.22 mg HC/g rock stipulates geological controls over the immature to moderately matured source rock potential (poor-fair) (Table 3). The relatively higher values of S2 (0.57 - 11.98 mg HC/g rock; except shaly coal sample CG#1438 - 39.45), point towards less cracking of hydrocarbon compounds (fairexcellent) (Table 3). The values of S3 varies from 0.36 - 2.78, specifying the substantial amount

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of CO2 and CO generation while cracking of hydrocarbon compounds. The HI is used to determine the kerogen type ranges from 30 - 253 mg HC/g TOC, PI gives the collective hydrocarbon production from the organic matter varying from 0.01 - 0.09 and oxygen index (OI) ranges from 11 - 53 mg HC/g CO2. These values are consistent with the requisite standard of the

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source rock which shows fair to very good source rock potential (Espitaliè et al., 1977; Tissot and Welte, 1984; Varma et al., 2015). The kerogen type is an important factor in determining the

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source rocks window (oil or gas) (Tissot and Welte, 1978; Peters et al., 2006). The Type I and Type II kerogen are prone for oil genesis. Whereas, the Types III and IV kerogen are usually characterized by terrigenous organic matter prone to generate wet and dry gases, mainly derived from woody materials (Peters et al., 2006; Hakimi et al., 2013; Mendhe et al., 2017a). The plot of HI vs Tmax shows the III and IV type of kerogen, except sample CG#1439 placed within the II-III kerogen Type. The range value of Tmax of studied shale samples ranges from 423 to 470 oC, elucidating immature to mature hydrocarbon generation potential (fair to excellent) (Fig. 5, Table 3). The variable thermal maturity may be due to the variation in lithology, depth of occurrence and the state of preservation of the organic matter. The Plot of OI and HI on a modified van Krevelen diagram (Fig. 6), illustrates the predominance of type III kerogen. The

MANUSCRIPT majority of the samples fromACCEPTED BH-2, BH-3 and BH-4 have HI Values >50 HC/g TOC displaying type III (gas prone) with lower thermal maturity (Table 2). The shale samples having significant TOC value (1.88 - 6.99 wt.%; except shaly coal sample CG#1438: 21.34 wt.%) with low hydrogen index (<200 mg HC/g rock) are of type III gas-prone kerogen (Jarvie et al., 2007). The HI value >200 mg HC/g rock are an admixture of type II-III kerogen (Fig. 7). The HI values between 82 and 283 mg HC/g TOC and excellent

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TOC (> 4.0 wt.%) have been observed for two sample from BH-2 (CG#1430 and CG#1434), from BH-3 (CG#1437 and CG#1438) and one sample from BH-4 (CG#1440) demonstrating potential gas-prone source rocks (Fig. 7, Table 3). The S2 and TOC content of shale core samples shown excellent positive correlation (Fig. 8; R2=0.92) specifying that hydrocarbon

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compounds are mainly contributing to TOC content (Jarvie et al., 2007). 4.3. Petrographic facies

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The maceral compositions of studied shale samples dominated by vitrinite (2.0 - 16.2 vol.%) and liptinite (0.2 - 22.0 vol.%) with apparently rich in alginite varied from 0.2 - 4.6 vol.% with an average value of 1.6 vol.%. The inertinite maceral ranges from 0.8 - 14.0 vol.%, signifying a low thermal transformation of organic matter to hydrocarbons (Table 4). The maceral distribution in shale bed, describes depositional conditions during sedimentation, pre and post diagenesis process, the input of the type of source materials and kerogen types (Tissot

et al., 2018b).

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and Welte, 1984; Mukhopadhyay et al., 1984; Diessel, 1986; Diessel, 1992; Hunt, 1995; Mendhe

The lath-shaped collotellinite and discrete vitroderinite grains are homogeneous in shape associated with clay minerals (Fig. 9a, d, g and h) (Taylor et al., 1998). The sporinite grains are

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characterised as more or less lensoidal shaped in a section parallel to the bedding cavity appear as a thin line, size of sporinite can vary from 5 to 350µm (Fig. 9b and c). The grains of alginite

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macerals appear to be more or less sponge to lensoidal (Fig. 9e). The larger content of vitrinite and alginite maceral may be considered as good indicator of source rock potential (Taylor et al., 1998; Mendhe et al., 2017a and e). The lath shaped inertinite (semifusinite) with well-preserved cell structure and shape of cavities vary in size and with very high reflectance and numerous thin natural fractures (Fig. 9f). The maceral composition of the shale has been studied in detail, to obtain a microfacies classification and to deduce palaeo-environments during shale deposition. The volumetric percentages of the three maceral groups, vitrinite, inertinite and liptinite are presented in the ternary diagram (Fig. 10a) to provide the fundamental information on thermal maturity. It is substantiated that the shales of Ib-River Mand-Korba Basin are vitrinite rich. The ternary plot of vitrinite+inertinite, liptinite and mineral matter distributions showing all the studied samples

ACCEPTED MANUSCRIPT contains type III kerogen placed in thermal-wet gas prone region (Fig. 10b) (Tissot and Welte, 1978; Hakimi et al., 2013; Mishra et al., 2016 and 2018a; Mendhe et al., 2017e). The distribution of organic content categorised into three categories i) <4 low organic content, ii) between 4 - 8 fair organic content and iii) excellent organic content <8. It may be observed that the wide variation in TOC distribution controlled by weathering, transportation and accumulation conditions (discuss in previous sections) (Mendhe et al., 2017e; Mishra et al.,

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2018a). However, most of the shale samples are placed in a fair, organic content category, implicates very good source rock potential (Fig. 11). The plot of TOC and mineral matter (Fig. 12) has shown the exponential relationship (R2=0.81), validating the observation made in Fig. 3b.

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4.4. Reconstruction of organic matter

The original hydrogen indexes (HIo), total organic carbon (TOCo) and reconstruction of

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organic matter conversion factor were assessed from disseminated maceral contribution, using the following Jarvie et al., (2007) equations. The HIo value can be computed from visual kerogen assessments and assigned kerogen-type HIo average values using the following equation 1. This equation requires the input of maceral percentages from visual kerogen assessment of a source rock.

 =

%  ×) 

% × 

× ×

%   ×) 

×

%  ×) 

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 =

%  × 

×

%  × 

×

×

%  ×) 

%  × 

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 ! "#$% ⁄#&% )() % "#$ ! ⁄#& ! )()

 = 1 − 

./.// ! )×123 ! #5)././/#123 4 ! )6 ! 123 ! )(

(2) (3) (4)

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*+,- = $

(1)

Original total organic carbon (TOCo) is the total organic carbon that gives sign about the

maximum quantitative potentiality of source rock to generate hydrocarbon depending on kerogen type with the support of HIo value (Equation 2; Jarvie et al., 2007). The extent of organic matter conversion (fractional) can be determined by the equations of Claypool and Mancini (1989). The fractional conversion, , is derived from the change in HIo to present-day values (HIPD) (Espitaliè et al., 1984; Peters et al., 2006), where PI is the production index (S1/(S1+S2)) as PIo= 0.02 to PIPD (Peters et al., 2006). The calculated value of total organic carbon (TOCo) and hydrogen index (HIo), ranges from 2.03 - 23.3 wt.% with average 5.39 wt.% and 130.26 - 480.99 mg HC/g TOC with average 248.4 mg HC/g TOC respectively.

ACCEPTED MANUSCRIPT The excellent correlation between TOC o vs TOCPD indicates uniformity in the conversion of organic matter to hydrocarbons (Fig. 13a, R2=0.9866). The plot of S1+S2 vs TOCo illustrated that the studied shale beds have good to excellent gas generation potential (Fig. 13b). The relationship between VRo and hydrocarbon generation (HIo and HIPD) is negatively dependent on the type of kerogen present within the studied shales (Fig. 14a and b). Inconsistencies due to changes in organic facies or the chemistry of the source rock can produce shifts in the HI data

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which are not indicative of maturation trends. HIo and HIPD provide an indication of the primary products that can be generated (e.g., oil, mixed, wet gas, dry gas) as well as tendencies of conversion from original source materials (Fig. 14c). The plot of HIo and S1+S2, represents the hydrocarbon yield of shale sammples from Ib-River Mand-Raigarh Basin (Fig. 14f).

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4.5. Evaluation of mineralogical phases

The mineral composition of the shale is important and promising parameters which

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influence the reservoir property (Ross and Bustin, 2009; Mendhe et al., 2017a, e; Mishra et al., 2018a). Studied shale beds of Ib-River Mand-Korba Basin, comprise mainly composed of clay minerals, quartz, k-feldspar, and carbonates (Table 5).

The XRD patterns of the studied shale (Fig. 15a, b, c and d) reveals that studied shale bed are dominated by mainly clay minerals which include kaolinite and illite ranges from 30.5 - 62.4 wt. %, with an average of 48.92 wt.%. Non-clay minerals include quartz and orthoclase (in few

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samples), ranges from 26.3 - 60.5 wt.% with an average of 41.59 wt.%. Carbonate minerals mainly siderite recorded, ranges from 1.2 - 20.1 wt.% with an average of 7.05, although few samples are devoid of carbonate minerals. Mineral distributions were plotted as a ternary

16a and b).

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diagram with different silicate members and carbonates, clay and silicates as end members (Fig.

4.6. Evaluation of inorganic facies

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Major elemental oxides distribution provides information regarding paleoclimatic depositional condition (Mendhe et al., 2018b). The distribution of major oxide composition obtained through XRF analysis exhibited in Table 6. It may be observed that the shale samples contain SiO2, Al2O3, Fe2O3, value ranges from 45.98 - 65.29, 21.12 - 36.84 and 3.24 - 24.69 wt.% respectively. The other oxides like K2O, CaO, MgO, TiO2, P2O5, Na2O, SO3, BaO and MnO values are varying from 1.76 - 3.92, 0.02 - 1.74, 0.55 - 2.02, 0.87 - 2.14, 0.03 - 1.01 0.05 0.12, 0.01 - 0.25, 0.05 - 0.12 and 0.02 - 0.70 wt.% respectively. The degree of weathering and alteration of source materials can be assessed by the amount of clay minerals comparative to non-clay phases in the shale beds. Evaluated the indices considering the ratio of the volumetric concentrations of aluminium oxides with respect to calcium, sodium and potassium oxides. The chemical index of alteration (CIA) suggested by

ACCEPTED Nesbitt and Young, 1982, McLennan et al.,MANUSCRIPT 1993 and the chemical index of weathering (CIW) estimated following Harnois, 1988. The CIA and CIW calculated using equation 5 and 6 respectively as below. ,7 = 89

9: 2;

: 2; 63<26=<: 26>: 2

9: 2;

9: 2; 63<26=<: 2

(5)

? × 100

(6)

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,A = 8

? × 100

The values of CIA and CIW ranged from 82.24 - 94.99 % and 91.99 - 99.65 % respectively and have been considered as crucial parameters used to identify the climatic condition. Usually, the CIA has been applied to the study of the climatic condition during deposition of sediments

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(Wu et al., 2005; Kim et al., 2014; Varma et al., 2018). The high values of CIA indicate tropical warm and humid climate conditions leading to strong chemical weathering during shale deposits. The main source of the fluvio-lacustrine sediments in the Ib-River Mand-Raigarh Basin was k-

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feldspar (granitic). The CIA plot of rock, minerals and clays displays sediments passed through strong chemical weathering resulting formation of kaolinite, illite and chlorite (Fig. 17) (Nesbitt et al., 1996; Young, 2002). Similarly, the composition of non-quartz components of the shale samples were evaluated by calculating the Index of Compositional Variation (ICV) suggested by Cox et al., (1995) as:

C : 2; 6>: 26=<: 263<26DE26DF261G2: 1G2:

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,B =

(7)

The ICV values observed in the range from 0.23 - 1.01 (Table 6). According to Cox et al., 1995, the ICV value <1 indicates the dominance of clay minerals whereas its value >1 indicates

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more rock-forming minerals like muscovite, K-feldspar, plagioclase, pyroxenes etc. Most of the studied shale has ICV values <1 point towards the presence of more clay minerals and less rock-

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forming minerals (Saikia et al., 2015). Another index of mudrock composition is the ratio of K2O/Al2O3 (Cox et al., 1995), which is excluding the influence of Fe from pyrite and Ca from carbonate minerals. The lower values of K2O/Al2O3 varying narrowly from 0.05 - 0.16 (average = 0.11) also suggests a predominance of clay minerals like kaolinite, illite and chlorite over the K-bearing minerals like feldspars and muscovites (Cox et al., 1995) (Table 6). The decrease in values of ICV with an increase in CIA indicates silicate minerals alteration containing Fe2O3, CaO and MgO and enrichment of non-silicate minerals like carbonates and sulphides derived from the secondary process (Fig. 18) (Cox et al., 1995). Similarly, the inverse relationship of Al2O3 with CaO suggests relative interdependency of silicates and carbonates alteration (Fig. 19a). The presence of Al2O3 leached out from the Fe2O3 iron-rich minerals like hematite and goethite, which likely formed under dry to temperate-tropical environment reveals

ACCEPTED MANUSCRIPT moderate to strong weathering process supporting formation of kaolinite, illite and other clay, which builds a porous matrix for gas storage (Fig. 19b) (Aleva, 1994). The strong positive correlation between Al2O3 and TiO2 exhibited in Fig. 19c (R2=0.78). It suggests that Ti and Al in Ib-River Mand-Raigarh shale deposits were associated with the carbonates and were concentrated in strongly weathered horizons. The reduction of K2O percentage with increasing concentration of Al2O3 signifies the intensive leaching and alteration of potash containing

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minerals to the depositional site and consequently subjected to diagenesis results in kaolinite formation (Fig. 19d) (R2=0.65). Similarly, the very good linear relationship between MgO and Al2O3, indicates the dissolution of carbonates (dolomite, limestone, calcite etc.) due to change in pH values of water (flood) transported the sediments to the basin, which subsequently acts as

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cementing material to the sandstone, shale and intercalations (Kim et al., 2014) (Fig. 19e). The sodium oxides mainly derived from the sediments deposited during marine transgression in post depositional conditions supported by Na ions for alteration of K-feldspar, biotite and serpentines

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initiating the formation of smectites and chlorite clays (Fig. 19f) (Churchman and Lowe, 2012; Mendhe et al., 2018a; Mishra et al., 2018b; Varma et al., 2018). Finally, it is interpreted from the relationships between the different oxides that leaching, dissolution, cementation and alteration of minerals like dolomite, serpentines, biotite, limestone, calcite etc. which may have blocked the pore openings, fractures and cracks causing poor pore connectivity (Mendhe et al., 2018a). The ternary plot of oxides like SiO2, Al2O3 and Fe2O3+MgO+CaO+K2O+Na2O+TiO2 is

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exhibited in Fig. 20a. The abundance of silicates in shales followed by aluminium oxides indicates the source of sediments as a function of chemical and physical weathering derived from K-feldspar, quartz and gneissic rocks. The chemical index of alteration (CIA) of siliciclastic

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rocks is one the technique to estimate the paleo-weathering intensity of the source rocks (Nesbitt and Young, 1982). The absence of K-feldspar in most of the samples illustrates extensive cyclic weathering of silicates except sample CG#1437 and CG#1438 (Table 5). However, the large

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amount of quartz content (26.00-57.60 %) and minerals like siderite formed during post depositional conditions (1.20 - 20.10 %) indicating leaching and residual effect on the sediments. Because, during the weathering of parent rocks, the elements like Na, K, Ca, and Mg are mainly leached out (Wu et al., 2005). The little Fe2O3 content in shales may be possibly contributed by the oxidative weathering of the outcrop. Consequently, the oxidative weathering of the sulfides associated with the organic matter and hydrocarbon accumulations supports the formation of large amounts of iron-rich secondary minerals such as iron oxides and carbonates (Mishra et al., 2018b). In advancement of chemical weathering, the clay minerals are produced with the alteration and disintegration of feldspars and other minerals, as a function of loss in Na and K (Nesbitt and Young, 1982; Rollinson, 1993). The abundance of clays like kaolinite and illite

MANUSCRIPT resulting from the siliciclasticACCEPTED sequences have gone through the diagenetic process by addition of potash containing minerals (Fedo et al., 1995). The CN–K–A diagram (CaO+Na2O, K2O, Al2O3) and CIA show the trend of weathering tending towards the Al2O3 peak (Fig. 20b). The studied shales values of CIA ranging between 82 and 95, placed in moderate to strong weathering (Fig. 20b; Table 6), similar observations also recorded by Mani et al., (2016). According to Roser and Korsch, 1988, the tectonic discrimination plot of K2O/Na2O and

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SiO2 may be used to mark the active or passive margin of the basin (Fig. 21). The passive stable tectonic setting of Ib-River Mand-Raigarh Basin favours organic deposition and their preservation to form a potential gas reservoir. The high range of silicates depicts relatively dry forest swamp condition of deposition supported by geochemical indices (CIA, CIW and ICV)

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(Warbrooke, 1987). Also, a variation in the chemical composition is in response to the relative abundance of mineral quartz in the coarse-grained fraction and clay minerals in the finegrained/clay fraction.

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The relationships of SiO2/Al2O3 and Fe2O3/K2O ratios showing major oxides can be used to identify mineral phases, and the sedimentation is resulting supportive reservoir properties (Fig. 22). It may be observed that the redox sensitive minerals reflect variations in lithology and preservation of organic material. The sedimentary facies boundaries tend to correspond with changes in major mineral concentrations during formation of clays containing shales. It is emphasized that the slowly accumulating sediments might have supported deposition of organic

generation and storage. 5.

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matter under reducing environment acted by anaerobic bacteria, favourable for rapid methane

Summary and Conclusions

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A thorough investigation has been carried out for shale beds of Ib-River Mand-Raigarh Basin, India considering organo-mineralogical assemblages and their significance to gas

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reservoir. Following conclusions have been drawn from this study. i. The moderate to high vitrinite and TOC content of shales suggests fair to excellent source rock potential for gas. Whereas, S1 and S2 indicated fair to very good source rock potential The plot of HI and OI, Tmax and HI and TOC and HI illustrated the presence of type II and III kerogen in studied shales prone for wet to dry gas generation. ii. The larger content of vitrinite and alginite maceral may be considered as a good indicator of source rock potential. iii. The uniformity in carbon conversion elucidates negligible effects of intrusive and basin tectonics on shale reservoir which is validated from the passive stable tectonic setting of IbRiver Mand-Raigarh Basin which favours deposition of organic matter.

ACCEPTED MANUSCRIPT iv. The high range of silicates depicts relatively dry forest swamp condition of deposition supported by geochemical indices like CIA, CIW and ICV. v. The decrease in values of ICV with an increase in CIA indicates silicate minerals alteration containing Fe2O3, CaO and MgO and enrichment of non-silicate minerals like carbonates and sulphides derived from the secondary process. vi. The presence of Al2O3 leached out from the Fe2O3 iron-rich minerals like hematite and

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goethite, which likely formed under dry to the temperate-tropical environment reveals moderate to strong weathering process supporting formation of kaolinite, illite and other clay, which builds a porous matrix for gas storage.

vii. The high percentage of quartz signifying the resistive nature of SiO2 towards erosion and

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weathering. However, non-occurrence or low percentage of K-feldspar and a large percentage of kaolinite attributed to the strong weathering conditions.

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Acknowledgement

Authors are thankful to the Dr P. K. Singh, Director, CSIR-CIMFR Dhanbad and Prof Rajiv Shekhar, Director, IIT(ISM), Dhanbad, for granting permission to publish this paper. We are also grateful to Ministry of Coal, Govt. of India Grant No. CE(EoI)/30 for funding Grant-inAid S & T [CE(EoI)/30] project of “Shale gas potentiality evaluation of Damodar Basin of India” under which this research has been carried out.

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Authors are also thankful to the learned Executive editor Dr Omer Inanc Tureyen and four

manuscript.

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anonymous reviewers for their constructive comments and suggestions to improve the

List of Abbreviations and Symbols - borehole - moisture content - volatile matter - fixed carbon - total organic carbon - carbon dioxide - carbon monoxide - Maximum temperature - hydrogen index - oxygen index - production index - original hydrogen index - original production index - original TOC content - present-day hydrogen index - present-day production index - present-day total organic carbon

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BH Moist VM FC TOC CO2 CO Tmax HI OI PI HIo PIo TOCo HIPD PIPD TOCPD

References

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- alginite on mineral ACCEPTED matter free basis MANUSCRIPT - liptinite on mineral matter free basis - vitrinite on mineral matter free basis - inertinite on mineral matter free basis - fractional conversion - chemical index of alteration - chemical index of weathering - index of compositional variation - mudrock composition - X-ray diffraction - X-ray fluorescence - telinite - collotelinite, - vitrodetrinite - collodetrinite - corpogelinite - perhydrous vitrinite - fusinite - semifusinite - micrinite - inertodetrinite - resinite - brown resinite - alginate - suberinite - cutinite - sporinite - mineral matter - vitrinite reflectance

Ammf Lmmf Vmmf Immf f CIA CIW ICV MC XRD XRF Te Co Vd CoD Cg PhV Fu Sf Mic Id Re Bre Alg Sub Cut Sp MM VRo

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Table 1: Megascopic and proximate properties of studied shales. Depth (m)

CG#1427

230

CG#1428

240

CG#1429

219

CG#1430

254

CG#1431

296

CG#1432

234

BH-1

BH-2

BH-3

CG#1433

348

CG#1434

104

CG#1435 CG#1436 CG#1437

176 272 158

CG#1438

185

CG#1439 CG#1440

84 101

CG#1441

140

CG#1442

218

BH-4

FC

Homogeneous dark grey shale with thin silt bands, dull lusture, fractures along the bedding planes. Grey to dark grey shale with unparalleled siltstone laminae, dull lusture, even fracture, visible minerals like quartz, feldspar and mica Banded shale of grey to dark grey contains alternate bands of clay and silts, disseminated black fragments of vegetal materials, conchoidal fracture

1.54

85.85

10.86

1.75

1.21

87.34

10.38

1.07

2.03

87.32

8.33

2.32

Light grey silty shale, uneven fracture, small rounded altered grains of quartz and mica Banded shale contains mainly silts and thin laminae of organic matter, dull lusture, subrounded quartz and flecks of mica Homogeneous dark grey shale mainly consist of clays, thins bands of silts, dull lustre, uneven fracture

1.73

87.72

9.43

1.12

1.69

86.74

10.17

1.4

1.41

83.08

12.81

2.7

Partially tilted intermixed silt bands indicating variations in river currents, dull lusture, uneven fracture and small flecks of mica

1.00

87.55

9.99

1.46

1.42

84.59

10.47

3.52

1.63

88.34

9.09

0.94

2.81

81.83

11.34

4.02

4.32 2.20 1.95

85.05 84.98 83.96

9.13 9.88 10.45

1.50 2.94 3.64

2.57

69.33

16.52

11.58

3.27 2.67

85.10 82.42

10.45 10.82

1.18 4.09

2.46

89.26

7.16

1.12

2.32

79.29

17.16

1.23

4.25

82.35

11.74

1.66

2.35

88.81

8.42

0.42

RI PT

155

VM

SC

CG#1426

Ash

M AN U

55

Moist.

Dark grey shale intermixed with silt sediments, visible dispersed organic matter, dull lusture, slickensides, irregular fractures and flecks of mica Banded shale with alternate bands of siltstone-mudstone and organic rich clay, dull lusture, uneven fracture, visible grains of quartz and mica

TE D

CG#1425

Proximate analysis (wt.%)

Megascopic descriptions

Homogeneous carbonaceous dark grey shale, dull lusture and uneven fracture Dark grey to black shale with cavities of silts, dull lusture disseminated vegetal materials presents, imprints of fossils, visible ferruginous and xylitic material Light grey shale with uniform thin layers of white clay, massive compact, dull lusture and uneven fracture

EP

Sample No.

Dark grey shale with siltstone-mudstone tilted lamination indicating variations in flood currents, dull lusture and uneven fracture

AC C

BH. No

Homogenous carbonaceous dark grey shale, dull lusture, even fracture, disseminated fragments of vegetal materials. CG#1444 Light grey shale with massive siltstone wavy laminae, disseminated fragments of vegetal materials, uneven 321 fracture and small flecks of quartz and mica Explanations: BH - borehole, Moist. - moisture content, VM - volatile matter, FC - fixed carbon. CG#1443

289

ACCEPTED MANUSCRIPT

Table 2: Results of TOC, Rock-Eval pyrolysis, reconstruction of organic matter and carbon conversion of shale core samples.

Sample No.

S1 (mg HC/g rock)

S2 (mg HC/g rock)

S3 (mg CO2/g rock)

PI (%)

HI (mg HC/g TOC)

OI (mg CO2/g TOC)

Tmax (0C)

TOC (wt.%)

CG#1425

0.08

0.88

0.66

0.08

33

25

431

CG#1426

0.05

0.57

0.36

0.08

30

19

CG#1427

0.06

1.43

0.44

0.04

37

11

CG#1428

0.05

0.87

0.38

0.06

46

20

CG#1429

0.11

1.96

0.72

0.05

68

25

CG#1430

0.12

4.04

2.61

0.03

82

53

CG#1431

0.10

1.16

0.44

0.08

46

17

CG#1432

0.10

1.65

0.89

0.06

40

CG#1433

0.10

0.98

0.45

0.09

37

CG#1434

0.15

8.11

1.14

0.02

128

CG#1435

0.11

5.38

0.96

0.02

160

CG#1436

0.12

2.88

1.18

0.04

65

CG#1437

0.05

3.11

1.42

0.01

CG#1438

0.22

39.45

2.78

0.01

CG#1439

0.09

11.98

1.11

0.01

CG#1440

0.08

7.43

1.31

0.01

CG#1441

0.06

4.93

0.75

0.01

CG#1442

0.05

2.49

1.38

CG#1443

0.07

5.31

CG#1444

0.04

0.85

Reconstruction of organic matter HIo (mg HC/g

f-conversion factor (in fraction)

2.64

2.90

139.81

0.79

453

1.90

2.15

167.18

0.84

431

3.83

4.48

211.80

0.85

454

1.91

2.07

136.22

0.69

428

2.88

3.65

311.54

0.83

423

4.94

6.44

353.61

0.83

436

2.52

2.73

139.09

0.70

21

433

4.16

4.80

200.90

0.83

17

470

2.67

2.92

141.41

0.76

18

428

6.35

9.22

480.99

0.82

29

434

3.36

3.94

316.18

0.57

27

427

4.40

5.26

257.47

0.79

52

24

430

5.99

6.68

177.11

0.74

185

13

427

21.34

23.30

295.21

0.44

253

23

428

4.73

5.10

321.26

0.27

106

19

429

6.99

7.85

232.80

0.60

174

26

432

2.84

3.28

310.54

0.52

0.02

91

50

426

2.75

3.39

302.15

0.76

1.16

0.01

118

26

430

4.50

5.64

343.04

0.73

0.87

0.04

45

46

432

1.88

2.03

130.26

0.68

SC

M AN U

TE D

EP

AC C

RI PT

TOC0 (wt.%)

Explanations: S1 - free hydrocarbons present in the rock (mg HC/g of rock), S2 - remaining generation potential (mg HC/g of rock), S3 - oxidizable carbon (mg CO2/g rock), PI Production index denoting ratio of free hydrocarbon to total hydrocarbon [S1/(S1+S2)], Tmax (°C) - maturity parameter based on the temperature at which the maximum amount of pyrolyzate (S2) is generated from the kerogen in a rock sample, TOC (wt.%) - total organic carbon, HI - hydrogen Index [(S2/TOC) × 100 mg HC/g TOC], OI - oxygen index [(S3/TOC) × 100 mg CO2/g TOC], TOCO - original TOC content present in shale samples, HIO - original hydrogen index present in shale samples.

ACCEPTED MANUSCRIPT

SC

Excellent >1.00 >5.00 >300 >460 >5.00

M AN U

Very good 0.50-1.00 3.00-5.00 200-300 440-460 3.00-5.00

TE D

Fair 0.10-0.50 0.50-3.00 100-200 420-440 1.00-3.00

EP

Poor <0.10 <0.50 <100 <420 <1.00

AC C

Parameters S1 S2 HI Tmax TOC

RI PT

Table 3: Shale gas genesis potential categorisation using pyrolysis and TOC properties.

ACCEPTED MANUSCRIPT

Table 4: Results of petrographic analysis and vitrinite reflectance of shale core samples.

-

Total vitrinite (vol. %.) 8.7

0.4

0.8

-

-

-

11.9

1.2

1.0

-

-

1.8

11.8

0.8

-

-

-

8.2

-

-

-

1.0

8.0

0.8

2.9

-

-

-

10.4

2.2

2.8

0.2

-

-

0.8

5.6

5.8

0.8

1.4

CG#1433

1.4

6.2

4.6

0.2

CG#1434

0.0

0.4

1.6

CG#1435

0.8

3.6

4.2

CG#1436

1.2

4.8

4.8

-

CG#1437

2.2

7.6

4.2

0.8

CG#1438

3.4

6.8

2.0

2.0

CG#1439

1.8

2.4

3.6

CG#1440

0.8

3.4

CG#1441

0.2

CG#1442

Cg

PhV

CG#1425

0.8

4.7

3.2

-

-

CG#1426

1.4

5.7

3.4

1.4

CG#1427

1.2

3.6

5.2

CG#1428

3.6

2.4

2.2

CG#1429

1.2

3.4

2.4

CG#1430

3.2

4.3

CG#1431

4.8

CG#1432

Inertinite (vol.%.) Fu Sf Mic Id

Liptinite (vol.%.) Alg Sub Cut

Total inertinite (vol. %)

Re

Bre

2.2

3.4

0.6

-

-

0.2

0.8

3.0

6.0

1.6

-

0.4

0.6

2.0

1.6

2.4

6.8

1.2

0.2

-

1.4

1.0

1.4

1.4

4.6

RI PT

Te

Vitrinite (vol.%.) Co Vd CoD

0.2

0.8

0.8

1.8

10.0

-

0.4

-

0.4

1.8

16.2

0.6

1.4

1.4

3.0

-

-

12.4

0.8

0.8

1.0

-

-

-

2.0

-

0.2

-

-

-

8.6

1.4

1.8

-

-

10.8

1.6

3.0

-

0.2

15.0

1.2

2.0

-

0.2

14.4

2.8

7.2

0.6

-

-

4.0

11.8

0.8

1.2

5.8

2.2

0.2

-

12.4

2.4

4.4

2.4

-

-

-

7.0

0.8

0.2

1.8

2.2

-

-

8.4

12.6

0.6

CG#1443

1.2

4.2

3.2

-

-

-

8.6

0.8

CG#1444

2.2

0.6

3.0

0.2

-

-

6.0

Total liptinite (vol. %)

MM (vol.%.)

VRo (%)

-

0.6

1.4

86.5

0.73

-

0.6

3.2

78.9

0.78

-

0.8

1.8

-

2.4

6.4

75.0

0.83

-

-

0.2

-

-

-

0.2

90.2

0.96

3.6

-

1.6

2.8

-

2.8

10.8

76.6

0.85

3.6

3.2

13.6

1.8

1.4

0.2

1.8

22.0

64.0

0.87

0.8

-

-

0.2

-

-

-

0.2

89.0

0.86

6.4

0.8

1.8

1.2

-

-

1.4

5.2

72.2

0.87

2.6

5.2

1.0

-

-

0.2

0.2

0.8

2.2

80.2

0.95

-

4.6

4.8

3.4

-

4.6

5.0

0.8

7.8

21.6

71.6

0.83

-

3.8

7.0

3.2

2.0

2.0

4.0

-

3.8

15.0

69.4

0.69

M AN U

SC

1.4

-

2.4

7.0

3.1

1.2

1.2

2.0

-

2.8

10.3

71.9

0.81

5.0

9.2

1.4

3.8

0.2

-

-

1.2

6.6

69.2

0.76

3.4

14.0

0.8

-

3.8

5.2

-

9.8

19.6

52.0

0.71

0.2

2.4

4.6

3.8

-

2.4

3.2

-

4.3

13.7

69.9

0.67

1.6

-

5.6

9.6

2.2

-

1.4

2.8

-

3.0

9.4

68.6

0.78

1.4

0.4

2.4

5.0

5.0

0.4

1.2

2.4

-

3.2

12.2

75.8

0.68

-

0.8

1.2

2.6

2.8

--

1.8

2.6

-

3.2

10.4

74.4

0.70

1.6

-

2.6

5.0

-

-

2.4

5.6

6.4

14.4

72.0

0.64

0.6

-

0.4

1.2

-

0.4

-

-

-

0.4

92.4

0.86

TE D

0.2

Sp

1.0

EP

AC C

Sample No.

-

Explanations: Te – telinite, Co – collotelinite, Vd – vitrodetrinite, CoD – collodetrinite, Cg – corpogelinite, PhV - perhydrous vitrinite, Fu – fusinite, Sf – semifusinite, Mic – micrinite, Id – inertodetrinite, Re – resinite, Bre - brown resinite, Alg – alginate, Sub – Suberinite, Cut – cutinite, Sp – sporinite, MM - mineral matter, VRo – vitrinite reflectance

ACCEPTED MANUSCRIPT

Table 5: Minerals and clay identified through XRD and their relative percentage calculated by Rietveld method. Non clay mineral (%) Orthoclase

Biotite

Siderite

CG#1425

32.4

-

-

-

32.4

CG#1428

37.6

-

-

-

37.6

CG#1430

26.3

-

-

2.6

26.3

CG#1433

35.4

-

-

-

35.4

CG#1434

45.1

-

-

1.2

45.1

CG#1437

42.4

18.1

-

1.8

60.5

CG#1438

26.0

8.9

-

-

CG#1439

57.6

-

-

3.7

CG#1442

41.1

-

8.3

20.1

CG#1444

45.0

-

3.2

12.9

Kaolinite

Illite

Total clay (%)

53.3

14.3

67.6

48.6

13.8

62.4

40.6

30.5

71.1

42.8

21.8

64.6

36.7

17.0

53.7

32.8

4.9

37.7

34.9

52.7

12.4

65.1

57.6

22.9

15.8

38.7

49.4

16.8

13.7

30.5

48.2

26.3

12.6

38.9

SC

M AN U

TE D EP AC C

Clay mineral (%)

RI PT

Quartz

Total non-clay (%)

Sample No.

ACCEPTED MANUSCRIPT

Table 6: Results of XRF analysis of shale core samples. Oxides (wt.%) SiO2

Al2O3

Fe2O3

K2O

CaO

MgO

TiO2

P2O5

Na2O

SO3

BaO

MnO

CG#1425

54.35

36.55

3.24

2.47

0.22

0.91

1.65

0.22

0.10

0.02

0.06

0.02

CG#1426

54.34

35.30

5.13

2.29

0.08

1.03

1.48

0.06

0.05

0.02

CG#1427

55.43

28.99

8.39

3.67

0.11

1.45

1.50

0.06

0.08

0.01

CG#1428

56.32

32.46

4.87

3.05

0.10

1.11

1.70

0.05

0.08

0.01

CG#1429

56.60

33.20

4.24

2.48

0.12

1.14

1.61

0.07

0.08

0.10

CG#1430

51.92

34.39

8.14

2.40

0.19

0.81

1.57

0.19

0.07

0.04

CG#1431

55.21

35.09

3.60

2.98

0.08

0.76

1.65

0.07

0.12

CG#1432

57.46

31.91

4.96

2.24

0.13

0.87

1.73

0.17

CG#1433

56.78

31.50

4.78

3.79

0.10

1.00

1.60

CG#1434

57.54

30.89

4.79

3.33

0.28

1.18

CG#1435

59.50

23.74

7.84

3.92

1.00

CG#1436

56.81

29.12

5.24

3.49

CG#1437

55.93

27.42

7.67

CG#1438

54.12

36.84

CG#1439

59.36

CG#1440

Total 99.80

Indexes

MC

CIA

CIW

ICV

92.92

99.13

0.24

0.07

0.03

99.85

93.59

99.65

0.29

0.06

0.08

0.06

99.82

88.23

99.34

0.53

0.13

0.06

0.03

99.84

90.96

99.46

0.34

0.09

0.06

0.03

99.72

92.54

99.40

0.29

0.07

-

0.12

99.83

92.82

99.25

0.39

0.07

0.02

0.05

0.22

99.83

91.71

99.44

0.27

0.08

0.08

0.04

0.05

0.09

99.72

92.87

99.34

0.32

0.07

0.05

0.09

0.01

0.09

0.03

99.83

88.77

99.4

0.36

0.12

1.44

0.07

0.08

0.03

0.08

0.11

99.83

89.33

98.85

0.36

0.11

2.00

1.06

0.44

0.12

0.04

0.07

0.11

99.84

82.49

95.48

0.68

0.16

1.34

1.20

1.29

1.01

0.08

0.02

0.11

0.08

99.80

85.56

95.33

0.44

0.12

3.91

1.08

1.47

1.12

0.80

0.10

0.08

0.07

0.15

99.81

84.34

95.88

0.57

0.14

3.69

1.76

0.13

0.55

2.14

0.31

0.05

0.04

0.07

0.02

99.72

94.99

99.51

0.23

0.05

23.48

7.93

3.68

1.18

1.85

1.15

0.71

0.11

0.05

0.12

0.24

99.83

82.55

94.80

0.69

0.16

57.23

29.65

5.21

3.64

0.48

1.45

1.32

0.03

0.09

0.22

0.12

0.04

99.46

87.58

98.14

0.41

0.12

CG#1441

65.29

23.58

3.99

3.70

0.33

1.36

1.19

0.11

0.12

0.02

0.12

0.04

99.84

85.05

98.16

0.45

0.16

CG#1442

45.98

21.12

14.69

2.26

1.74

CG#1443

54.16

23.59

12.82

3.63

1.35

CG#1444

61.73

27.69

4.16

3.21

0.02

TE D

M AN U

SC

0.06

EP

RI PT

Sample No.

0.87

0.52

0.10

0.02

0.09

0.70

99.88

83.75

91.99

1.01

0.11

2.02

1.02

0.56

0.12

0.25

0.08

0.22

99.82

82.24

94.16

0.90

0.15

1.02

1.46

0.06

0.08

0.02

0.09

0.02

99.57

89.32

99.64

0.36

0.12

AC C

1.78

Explanations: CIA - chemical index of alteration [Al2O3 /(Al2O3 + CaO + Na2O + K2O)] × 100, CIW - chemical index of weathering [Al2O3 /( Al2O3 + CaO + Na2O)] × 100, ICV - index of compositional variation, MC- mudrock composition (K2O/Al2O3).

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

Fig. 1: The geological map of Ib River-Mand-Korba basin showing the location of investigated boreholes (modified after Raja Rao, 1983; Coal Atlas of India, 1993).

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

Fig. 2: The generalized lithostratigraphy of the Ib-River Mand-Raigarh basin, Chhattisgarh (modified after Casshyap et al., 1988; Chakraborti et al., 2002).

Fig. 3: Megascopic photographs of shale core samples from the Ib-River Mand-Raigarh basin.

ACCEPTED MANUSCRIPT a

RI PT

b

AC C

EP

TE D

M AN U

SC

Fig. 4: Relationship of TOC with a) fixed carbon and b) ash yield.

Fig. 5: Plot of Tmax and hydrogen index showing kerogen type in shale samples.

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

Fig. 6: Plot of oxygen index and hydrogen index reflecting kerogen type (modified after van Krevelen diagram).

Fig. 7: Plot of TOC and HI showing shale samples placed in oil and gas window.

AC C

EP

TE D

M AN U

Fig. 8: Relationship of S2 and TOC of shale samples.

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

Fig. 9: Microscopic photographs of Barakar shale core samples showing variation in maceral distribution: a) lath shaped grain of collotelinite (CG#1429), b) elongated and lensoidal grain of sporinite (CG#1430), c) dispersed sporinite (CG#1434), d) pyrite grains filled in pores, dispersed grains of vitrodetrinite and clay (CG#1434), e) alginite (CG#1435), f) semifusinite lath along with clays (CG#1438), g) collotelinite, dispersed vitrodetrinite and clays (CG#1438) h) Macrinite and collotelinite (CG#1438).

ACCEPTED MANUSCRIPT

b

SC

RI PT

a

AC C

EP

TE D

M AN U

Fig. 10: Ternary diagram of petrographic facies a) vitrinite, liptinite and inertinite showing trend of maturation and b) maceral and mineral distribution illustrating kerogen type.

Fig. 11: Plot of TOC and total maceral showing the distribution of organic content.

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

Fig. 12: Plot of TOC and mineral matter content of studied shale samples.

b

AC C

EP

TE D

a

Fig. 13: Plot of (a) TOCo with TOCPD and (b) S1+S2 with TOCo.

b

c

RI PT

a

SC

ACCEPTED MANUSCRIPT

f

AC C

EP

e

TE D

M AN U

d

Fig. 14: Relationship of a) VRo vs HIPD, b) VRo vs HIo, c) HIo vs HIPD, d) total maceral vs HIo, e) TOCo vs HIo and f) S1+S2 vs HIo.

ACCEPTED MANUSCRIPT a

d

TE D

M AN U

SC

c

RI PT

b

AC C

EP

Fig. 15: XRD peaks showing the presence of clays and different minerals in studied shales, a) sample CG-1430, b) sample CG-1437, c) sample CG-1442 and d) sample CG-1444.

ACCEPTED MANUSCRIPT b

SC

RI PT

a

AC C

EP

TE D

M AN U

Fig. 16: Ternary facies diagram of mineral and clay content showing a) trend of mineral weathering and clay formation, b) alteration of silicates to form clay and carbonates.

Fig. 17: Position of Ib-River Mand-Raigarh Basin sediments on CIA plot of rock, minerals and clays (after Nesbitt et al., 1996; Young 2002).

M AN U

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Fig. 18: Relationship of CIA and ICV showing trend of silicate to non-silicate minerals alteration.

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Fig. 19: Relationship of different oxides in shale samples, a) Al2O3 vs CaO; b) Al2O3 vs Fe2O3; c) Al2O3 vs TiO2; d) Al2O3 vs K2O; e) Al2O3 vs MgO; f) Al2O3 vs Na2O.

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Fig. 20: Ternary diagrams showing intensity of chemical alteration (after Taylor and McLennan, 1985; Condie et al., 1992; Nesbitt et al., 1996).

Fig. 21: Tectonic discrimination plot of K2O/Na2O and SiO2 showing passive margin for Ib-River Mand-Raigarh Basin (after Roser and Korsch, 1986 and 1988).

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Fig. 22: Plot of SiO2/Al2O3 and Fe2O3/K2O showing terrigeneous sediments placed in shale and Fe-shale region (after Herron, 1988; Mani et al., 2016).

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Investigated organo-mineralogical constituents of shale beds of Ib-River MandRaigarh Basin, India.
The values of Tmax and VRo counsels moderately matured shales having type II/III kerogen prone for wet to dry gas genesis.
The uniformity in carbon conversion elucidates negligible effects of intrusive and basin tectonics.
The passive stable tectonic setting favours organic deposition and their preservation to form a potential gas reservoir.
High range of silicates depicts relatively dry forest swamp condition supported by geochemical indices (CIA, CIW and ICV).