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Source rock evaluation of Kharita and Bahariya formations in some wells, North Western Desert, Egypt: Visual palynofacies and organic geochemical approaches
Egyptian Journal of Petroleum xxx (2017) xxx–xxx
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Source rock evaluation of Kharita and Bahariya formations in some wells, North Western Desert, Egypt: Visual palynofacies and organic geochemical approaches Nabil Aboul Ela a, Sameh S. Tahoun a, Tarek Fouad b, Doaa A. Mousa b,⇑, Rehab Saleh b a b
Geology Department, Faculty of Science, Cairo University, P.O. Box 12613, Giza, Egypt Exploration Department, Egyptian Petroleum Research Institute, 1 Ahmed El-Zomor Street, El-Zohour Region, Nasr City, Cairo 11727, Egypt
a r t i c l e
i n f o
Article history: Received 2 April 2017 Revised 14 July 2017 Accepted 26 July 2017 Available online xxxx Keywords: Palynofacies Rock eval pyrolysis Bahariya formation Kharita formation North Western Desert Egypt
a b s t r a c t Palynofacies analyses were applied on ninety-one samples from the subsurface Albian – Cenomanian succession represented by Kharita and Bahariya formations, encountered in El-Noor, and South Sallum wells, located in the North Western Desert, Egypt, to visually characterize the content of dispersed organic matter, as well as, organic geochemical characterization to reveal the depositional paleoenvironments and source rock potentiality. The result recognized of five palynofacies associations in the studied interval. The deposition of Kharita Formation took place mainly in a steady and a relatively stable deltaic to marginal environment continued as well in the lower part of Bahariya Formation with minor changes. The marine influence became more common in the upper part of Bahariya Formation showing the exceptional high hydrocarbon potential recorded in the studied interval. This indicates marine transgression by the end of the early Cenomanian (Upper Bahariya) age. Samples from the Kharita Formation contain abundant brown phytoclasts which suggest gas-prone kerogen type III and IV. While Bahariya Formation includes translucent, brown cuticles and woody tracheid phytoclasts pointing to more promising gasprone kerogen type III. The organic geochemical analysis shows poor to fair gas-prone source rock potential within the study section., Thermally, the color of the spore grains in Kharita and Bahariya formations show that dark yellow to orange, indicates immature besides their general little poor hydrocarbon generation potentiality. Ó 2017 Egyptian Petroleum Research Institute. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction The studied wells El-Noor, and South Sallum are locates in the northern Western Desert between latitude (31° 190 36.91 6700 N, 26° 040 19.25 7700 E), located in the North Western Desert of Egypt (Fig. 1). The Albian- Cenomanian intervals which include Kharita and Bahariya formations are the most important rock successions in the subsurface of the Western Desert of Egypt. These two formations confine the essential petroleum deposits and represent the central target for exploration [1]. In the recent years, many studies were conducted to investigate the paleoenvironment of deposition
Peer review under responsibility of Egyptian Petroleum Research Institute. ⇑ Correspondence to: D.A. Mousa. E-mail addresses: [email protected] (N.A. Ela), [email protected] (S.S. Tahoun), [email protected] (T. Fouad), [email protected] (D.A. Mousa), [email protected] (R. Saleh).
during the Albian Cenomanian with special focus on palynofacies as a reliable tool for analysis [2–10]. Furthermore, the geochemical investigations of Kharita and Bahariya formations in the North Western Desert discussed by many authors [11–16], among of them recognized that the Kharita and Bahariya formations are ranges from immature to mature source rocks. The current investigations represent the additional contribution to the line concerning the applications of palynofacies in outlining the paleoenvironmental conditions and source rock evaluations with compatible results from organic geochemical analysis. This paper is focusing on the palynofacies and the geochemical analysis on the relatively closely spaced El-Noor and South Sallum wells. (Fig. 1). The main target of the present study is the identification of the palynofacies types, interpreting the depositional paleoenvironments, estimating the thermal maturation of the studied formations using the spore coloration. Finally, comprehensive source rock evaluation by integrating the results from palynofacies and geochemical analyses.
http://dx.doi.org/10.1016/j.ejpe.2017.07.009 1110-0621/Ó 2017 Egyptian Petroleum Research Institute. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article in press as: N.A. Ela et al., Source rock evaluation of Kharita and Bahariya formations in some wells, North Western Desert, Egypt: Visual palynofacies and organic geochemical approaches, Egypt. J. Petrol. (2017), http://dx.doi.org/10.1016/j.ejpe.2017.07.009
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N.A. Ela et al. / Egyptian Journal of Petroleum xxx (2017) xxx–xxx
2.1. Kharita formation It overlies conformably with the Dahab Formation and underlies the Bahariya Formation. It is composed mainly of sandstone that shows fining upward sequences, with shale and thin limestone streaks confined in certain areas. Thick sandstone units with minor shale intercalations characterize the lower part of this formation [17–18]. In El-Noor well, the depth interval of the Kharita Formation is between 7790–8590 ft (Fig. 2). This formation consists mainly of colorless, fine to coarse grained, poorly sorted and subrounded sandstone. In South Sallum well, the depth interval of the Kharita Formation is between 7552–8800 ft (Fig. 3). The lithological composition of this formation is colorless, fine to coarse grained, poorly sorted and subrounded sandstone.
2.2. Bahariya formation
Fig. 1. Location map of the studied El – Noor and South Sallum wells.
2. Lithostratigraphy The lithologies, unit thicknesses, and tops of Kharita and Bahariya formations in the studied interval in El Noor and south Sallum wells are discussed below.
It rests conformably or sometimes unconformably on the Kharita Formation and is overlain conformably by Abu-Roash Formation. It dates as late Albian – early Cenomanian and deposited under fluvial to shallow marine environment [17–18]. The described formation is dominated by near shore marine finegrained sandstone, interbeded with shale and siltstones. The basal part of the formation usually includes massive sands, but these sands are more shaley and less uniform than the sands of the underlying Kharita and it is dated as of Cenomanian age. In El-Noor well the depth interval of the Bahariya Formation is
Fig. 2. Lithostratigraphic colum, locations of the studied samples and palynofacies percentage vertical distribution of El Noor well.
Please cite this article in press as: N.A. Ela et al., Source rock evaluation of Kharita and Bahariya formations in some wells, North Western Desert, Egypt: Visual palynofacies and organic geochemical approaches, Egypt. J. Petrol. (2017), http://dx.doi.org/10.1016/j.ejpe.2017.07.009
N.A. Ela et al. / Egyptian Journal of Petroleum xxx (2017) xxx–xxx
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Fig. 3. Lithostratigraphic colum, locations of the studied samples and palynofacies percentage vertical distribution of of South Sallum well.
between 6350–7790 ft (Fig. 2). This formation is composed of greenish to white greenish, fine to very fine sandstone and moderately sorted, with glauconite cement. Shale in this formation is greenish grey to dark grey and firm. In South Sallum well the depth interval of the Bahariya Formation is between 6200–7552 ft (Fig. 3). it consists of interbeded sandstone, which is colorless, yellowish white, and shale, which is grey to greenish grey and flacky. The sandstone is fine to coarse grained, angular to subrounded and poorly sorted. In the upper part, this formation composed of marly limestone. 3. Material and methods Sixty-two (62) representative samples were prepared from El-Noor well, and twenty-nine (29) samples picked from South Sallum well in order to make qualitative as well as quantitative palynofacies analyses for the recovered particulate organic matter (POM), to delineate the different palynofacies assemblages and kerogen types variation throughout the studied formations in the studied intervals.
2. Eighteen (18) representative samples from El Noor Well were analyzed by Rock Eval-6 analyser to obtain the Organic geochemical data represented in Table 3. About 60 mg of washed, dry and fine grained sample is loaded in the crucible of the Rock Eval-6, the programmed run in the Rock Eval-6 to obtain the main screen analysis data for the studied samples, according to a programmed temperature pattern. The released hydrocarbons are monitored by a Flame Ionization Detector (FID), forming the so-called peaks S1 (thermo-vaporized free hydrocarbons) and S2 (hydrocarbons from cracking of organic matter). In addition, CO and CO2 released during pyrolysis can be monitored in real time by means of an Infrared (IR) cell. The method can be completed by oxidation of the rock sample according to a programmed temperature pattern. This complementary stage allows determination of Total Organic Carbon and Mineral Carbon content of the concerned samples. All these analyses were carried out in the Egyptian Petroleum Research Institute [EPRI].
4. Results and discussion 1. Extraction procedures involving dilute HCl and HF, wet sieving using 10m polyester sieves, and mounting by using UV liquid media. Quantitative analysis of the overall kerogen composition was carried out on sieved, unoxidized material. At least two slides of each sample were studied. Each slide was counted for its (POM) content, in which the first 500 particles were counted in terms of abundant (>35%), frequent (16–35%), common (5–15%) and rare (<5%) (Tables 1 and 2).
4.1. Palynofacies analysis The relative variations in abundances of the different palynofacies classes reveal the depositional environments. In addition the visual examination of the palynofacies indicates the hydrocarbon generation potentiality of the source rocks. Palynofacies is classified into three main classes, which are recognized using the
Please cite this article in press as: N.A. Ela et al., Source rock evaluation of Kharita and Bahariya formations in some wells, North Western Desert, Egypt: Visual palynofacies and organic geochemical approaches, Egypt. J. Petrol. (2017), http://dx.doi.org/10.1016/j.ejpe.2017.07.009
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N.A. Ela et al. / Egyptian Journal of Petroleum xxx (2017) xxx–xxx
translucent, dispersed particles of plant-derived kerogen other than palynomorphs. Tables 1 and 2 show the quantitative distribution of the various particulate organic matters (POM) recorded from El Noor and South Sallum wells respectively. These palynofacies assemblage are described as the following:
classification scheme of [19–20] Palynomorphs is classified into terrestrial (sporomorphs) or marine (dinoflagellates – foraminifera test linings). The Amorphous organic matter (AOM)) refers to all structureless, fluffy dispersed particles of kerogen, whether of marine or non-marine origin. It is derived from phytoplanktons or degradation of bacteria. Phytoclasts are structured, opaque or
Table 1 Quantitative distribution of particulate organic matter in El Noor well. Depth Pollen
Spore
Terr. Palynomorphs
Spore/ pollen
Terrestrial Dinoflagellate palynomorphs
Marine palynomorphs
Marine/ Terrestrial
Op. lath.
Palynomophs
WP
AOM
F.T.L
Phytoclast
6380 6420 6480 6520 6560 6600 6640 6680 6700 6740 6780 6820 6840 6880 6920 6960 7020 7060 7100 7140 7180 7220 7260 7300 7340 7380 7420 7460 7500 7560 7600 7640 7680 7720 7760 7800 7840 7880 7920 7980 8020 8040 8100 8140 8180 8220 8260 8300 8340 8380 8420 8460 8500 8540 8580 8600 8640 8680 8720 8760 8800 8840
2.22 2.11 0.20 1.06 0.15 2.77 1.88 4.59 1.57 1.46 2.78 2.15 1.34 1.41 3.40 1.43 1.78 3.28 1.32 2.46 2.90 1.65 2.13 4.31 4.44 1.41 0.88 1.46 1.70 5.96 2.75 1.66 2.69 0.92 1.50 1.09 0.84 0.58 0.62 1.46 0.63 0.64 1.11 0.84 0.65 0.56 2.30 0.28 0.58 0.66 0.47 0.39 0.15 0.42 0.94 1.06 1.16 0.63 0.32 0.23 0.45 0.46
3.91 3.24 2.78 5.75 0.98 5.70 2.78 5.31 1.90 1.74 3.59 2.70 2.05 1.80 5.71 2.83 2.76 4.35 3.45 5.07 6.75 2.51 3.23 8.37 6.23 1.94 1.21 1.90 2.00 7.38 3.84 2.97 3.83 1.51 2.49 1.60 1.07 0.76 0.78 2.62 0.79 0.90 1.84 1.55 1.03 0.89 3.63 0.38 0.95 1.05 0.73 0.50 0.21 0.61 1.25 1.42 1.57 0.68 0.39 0.29 0.65 0.63
2.09 1.91 0.08 0.25 0.18 0.97 2.09 9.60 5.61 5.94 4.07 4.76 2.00 3.95 2.02 1.12 2.08 4.10 0.66 1.01 0.85 2.13 2.20 1.46 3.47 2.78 2.83 3.77 6.19 5.30 2.85 1.29 2.94 1.61 1.66 2.26 3.99 3.45 4.17 1.86 4.84 2.66 1.59 1.21 1.78 1.76 2.19 2.80 1.61 1.78 1.82 3.56 2.38 2.30 3.28 3.40 3.40 15.14 4.33 3.75 2.39 2.97
3.28 3.21 2.78 5.40 0.98 5.63 2.77 5.06 1.85 1.71 3.46 2.60 2.01 1.76 5.09 2.71 2.63 4.08 3.32 4.89 6.32 2.43 3.10 7.26 5.72 1.92 1.19 1.85 1.98 7.08 3.72 2.94 3.60 1.49 2.40 1.57 1.06 0.75 0.77 2.25 0.77 0.89 1.81 1.53 1.02 0.87 3.35 0.37 0.94 1.03 0.72 0.50 0.21 0.61 1.23 1.37 1.50 0.68 0.39 0.29 0.64 0.62
4.40 0.66 0.13 0.75 0.02 2.83 0.16 0.59 0.06 0.05 0.15 0.13 0.06 0.05 0.67 0.13 0.15 0.44 0.16 0.33 0.49 0.12 0.23 1.37 0.69 0.07 0.03 0.06 0.05 1.14 0.30 0.14 0.40 0.04 0.12 0.05 0.02 0.01 0.02 0.39 0.02 0.02 0.05 0.03 0.03 0.02 0.31 0.00 0.02 0.02 0.01 0.01 0.00 0.01 0.03 0.06 0.11 0.01 0.00 0.00 0.01 0.01
1.34 0.21 0.05 0.14 0.02 0.50 0.06 0.12 0.03 0.03 0.04 0.05 0.03 0.03 0.13 0.05 0.06 0.11 0.05 0.07 0.08 0.05 0.07 0.19 0.12 0.04 0.02 0.03 0.03 0.16 0.08 0.05 0.11 0.03 0.05 0.03 0.02 0.02 0.02 0.17 0.03 0.02 0.03 0.02 0.03 0.02 0.09 0.01 0.02 0.02 0.01 0.01 0.00 0.01 0.03 0.05 0.08 0.02 0.01 0.01 0.01 0.01
11.14 67.92 42.63 40.61 20.63 14.17 63.74 52.55 47.04 40.04 64.92 48.54 37.76 43.64 23.06 32.89 39.36 37.72 38.38 59.44 27.79 37.57 45.79 35.65 34.45 45.24 44.99 36.18 42.68 49.95 57.59 56.92 50.34 57.49 39.61 40.18 48.28 84.02 65.21 63.36 68.48 74.77 54.64 61.45 58.70 67.14 56.62 61.77 70.14 69.62 68.82 39.06 58.60 56.67 57.73 51.64 54.44 69.34 69.55 59.02 64.94 66.53
7.68 3.87 2.91 6.14 1.00 8.46 2.93 5.66 1.91 1.76 3.61 2.73 2.06 1.82 5.76 2.84 2.78 4.52 3.48 5.22 6.81 2.54 3.33 8.64 6.41 1.98 1.22 1.91 2.03 8.22 4.02 3.08 4.00 1.53 2.52 1.62 1.08 0.76 0.78 2.64 0.79 0.90 1.86 1.56 1.04 0.89 3.66 0.38 0.96 1.05 0.73 0.51 0.21 0.62 1.26 1.43 1.61 0.69 0.39 0.29 0.65 0.63
30.38 19.86 51.67 35.44 32.58 27.56 28.94 36.31 46.46 44.86 25.57 43.09 55.46 49.38 67.17 53.69 49.50 49.51 46.28 25.70 50.68 49.32 42.27 34.54 39.62 46.43 51.17 60.30 48.78 28.43 32.52 32.31 38.63 29.97 38.45 44.34 40.04 10.96 28.77 32.10 29.85 22.11 38.73 27.88 34.00 30.20 30.42 32.70 26.14 26.58 26.28 40.28 38.43 38.81 33.22 43.44 43.15 25.86 25.93 36.64 32.90 31.38
50.80 8.34 2.80 17.81 45.79 49.80 4.40 5.47 4.59 13.35 5.90 5.64 4.72 5.17 4.01 10.59 8.35 8.25 11.85 9.64 14.71 10.57 8.61 21.17 19.52 6.35 2.62 1.61 6.50 13.40 5.88 7.69 7.02 11.01 19.42 13.86 10.60 4.26 5.23 1.90 0.88 2.21 4.77 9.10 6.26 1.78 9.30 5.15 2.76 2.74 4.17 20.14 2.76 3.90 7.79 3.48 0.81 4.11 4.13 4.05 1.52 1.46
3.77 0.63 0.13 0.39 0.01 2.77 0.15 0.34 0.01 0.02 0.01 0.03 0.02 0.02 0.06 0.01 0.02 0.17 0.04 0.15 0.06 0.04 0.09 0.27 0.19 0.04 0.01 0.01 0.03 0.84 0.17 0.11 0.17 0.02 0.04 0.02 0.01 0.01 0.01 0.02 0.00 0.00 0.02 0.02 0.01 0.00 0.04 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.04 0.00 0.00 0.00 0.00 0.00
41.52 87.79 94.29 76.05 53.21 41.73 92.67 88.87 93.50 84.89 90.49 91.63 93.22 93.01 90.23 86.58 88.87 87.23 84.67 85.14 78.47 86.89 88.06 70.19 74.07 91.67 96.16 96.48 91.46 78.38 90.11 89.23 88.98 87.46 78.06 84.53 88.32 94.98 93.98 95.46 98.33 96.88 93.37 89.33 92.70 97.34 87.04 94.47 96.28 96.20 95.10 79.35 97.03 95.48 90.95 95.08 97.58 95.20 95.48 95.66 97.84 97.91
1.06 1.10 2.57 4.33 0.83 2.87 0.90 0.48 0.28 0.25 0.68 0.45 0.67 0.36 1.69 1.28 0.85 0.80 1.99 2.43 3.42 0.78 0.97 2.95 1.28 0.51 0.31 0.39 0.28 1.12 0.97 1.28 0.92 0.57 0.90 0.48 0.21 0.17 0.15 0.79 0.13 0.24 0.70 0.69 0.37 0.31 1.05 0.10 0.36 0.37 0.26 0.11 0.06 0.18 0.29 0.31 0.34 0.04 0.07 0.06 0.19 0.16
0.63 0.03 0.00 0.36 0.01 0.07 0.01 0.25 0.05 0.04 0.13 0.10 0.04 0.03 0.61 0.12 0.13 0.27 0.13 0.18 0.43 0.08 0.13 1.11 0.51 0.03 0.02 0.05 0.02 0.30 0.12 0.04 0.22 0.03 0.09 0.03 0.01 0.01 0.01 0.38 0.02 0.02 0.03 0.01 0.01 0.02 0.28 0.00 0.01 0.02 0.01 0.00 0.00 0.00 0.02 0.05 0.07 0.01 0.00 0.00 0.00 0.01
The abbreviations used in these tables are (POM) Particulate Organic Matter – (Tr.) Terrestrial Palynomorph – (Mr.) Marine Palynomorph – (Tr.O) Translucent Organic Matter – (AOM) Amorphous Organic Matter – (Pl.) Pollen – (Sp.) Spore – (Dino.)Dinoflagellate – (OP.) Opaque Organic Matter – (Ph)Phytoclasts – (FTL) Foraminiferal Test Lining - (Paly.) Palynomorph.
Please cite this article in press as: N.A. Ela et al., Source rock evaluation of Kharita and Bahariya formations in some wells, North Western Desert, Egypt: Visual palynofacies and organic geochemical approaches, Egypt. J. Petrol. (2017), http://dx.doi.org/10.1016/j.ejpe.2017.07.009
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N.A. Ela et al. / Egyptian Journal of Petroleum xxx (2017) xxx–xxx Table 2 Quantitative distribution of particulate organic matter in South Sallum well. Depth
Pollen
Spore
Spore/ pollen
Terrestrial palynomorphs
Dinoflagellate
F.T.L
Marine palynomorphs
Marine/ Terrestrial
Palynomorphs
Op.lath.
WP
Phytoclast
AOM
6208 6272 6336 6400 6464 6528 6592 6656 6752 6816 6880 6976 7072 7168 7264 7360 7456 7552 7648 7744 7840 7936 8032 8160 8245 8352 8400 8544 8800
0.00 0.18 0.19 0.95 2.15 1.21 1.59 4.70 6.98 5.12 0.34 7.22 0.19 1.21 2.21 2.21 0.00 1.59 0.93 2.50 0.63 2.05 1.85 2.21 1.21 1.10 0.51 0.93 0.71
0.19 0.35 1.69 0.00 2.15 3.98 4.78 5.80 7.61 4.33 3.02 6.19 1.69 3.98 4.71 4.71 0.19 4.78 2.48 3.39 0.95 3.55 12.00 4.71 5.71 7.34 3.00 1.28 2.30
0.00 2.00 9.00 0.00 1.00 3.29 3.00 1.23 1.09 0.85 9.00 0.86 9.00 3.29 2.13 2.13
0.19 0.53 1.88 0.95 4.31 5.19 6.38 10.50 14.59 9.45 3.36 13.40 1.88 5.19 6.92 6.92 0.19 6.38 3.41 5.89 1.58 5.59 13.85 6.92 6.92 8.44 3.50 2.21 3.00
0.93 0.89 0.75 0.95 2.15 3.11 0.48 0.94 1.48 1.57 0.17 1.55 0.75 3.11 0.59 0.59 0.93 0.48 0.16 0.00 0.16 0.00 0.62 0.59 0.69 0.73 0.27 0.16 0.18
0.56 0.89 5.64 2.13 4.31 0.35 0.16 0.00 1.27 0.39 0.17 0.00 5.64 0.35 0.29 0.29 0.56 0.16 0.16 0.18 0.79 0.00 0.00 0.29 0.29 0.18 0.00 0.16 0.00
1.49 1.77 6.39 3.07 6.46 3.46 0.64 0.94 2.75 1.97 0.34 1.55 6.39 3.46 0.88 0.88 1.49 0.64 0.31 0.18 0.95 0.00 0.62 0.88 0.99 0.92 0.27 0.31 0.18
8.00 3.33 3.40 3.25 1.50 0.67 0.10 0.09 0.19 0.21 0.10 0.12 3.40 0.67 0.13 0.13 8.00 0.10 0.09 0.03 0.60 0.00 0.04 0.13 0.14 0.11 0.08 0.14 0.06
1.68 2.30 8.27 4.02 10.77 8.65 7.02 11.44 17.34 11.42 3.69 14.95 8.27 8.65 7.81 7.81 1.68 7.02 3.72 6.07 2.54 5.59 14.46 7.81 7.91 9.36 3.77 2.52 3.18
4.47 8.87 16.92 41.13 10.15 35.29 34.77 31.03 30.44 36.61 44.30 34.02 16.92 35.29 40.65 40.65 4.47 34.77 43.72 37.50 44.69 44.20 34.15 40.65 43.55 37.43 43.40 43.72 42.40
5.59 10.11 19.36 42.08 14.46 42.39 40.03 37.77 39.53 42.52 47.48 41.75 19.36 42.39 45.95 45.95 5.59 40.03 46.36 40.89 45.80 47.75 46.77 45.95 42.55 45.50 44.88 46.36 44.88
10.06 18.97 36.28 83.22 24.62 77.68 74.80 68.81 69.98 79.13 91.78 75.77 36.28 77.68 86.60 86.60 10.06 74.80 90.08 78.39 90.49 91.95 80.92 86.60 86.10 82.94 88.28 90.08 87.28
88.27 78.72 55.26 12.77 64.62 13.49 18.18 19.75 12.68 9.45 4.03 9.28 55.26 13.49 5.30 5.30 88.27 18.18 5.58 15.00 6.66 2.46 4.62 5.30 5.30 7.71 9.54 7.58 9.54
3.00 2.67 1.36 1.50 1.73 6.50 2.13 4.72 6.67 5.91 1.38 3.25
The abbreviations used in these tables are (POM) Particulate Organic Matter – (Tr.) Terrestrial Palynomorph – (Mr.) Marine Palynomorph – (Tr.O) Translucent Organic Matter – (AOM) Amorphous Organic Matter – (Pl.) Pollen – (Sp.) Spore – (Dino.)Dinoflagellate – (OP.) Opaque Organic Matter – (Ph)Phytoclasts – (FTL) Foraminiferal Test Lining - (Paly.) Palynomorph.
Table 3 Rock Eval-6 pyrolysis data for the geochemical analysis of El Noor well. Formation
Depth
TOC Wt%
S1 mg./g.
S2 mg/g
S3 mg/g
T max
HI
OI
PI
Bahariya
6560 6620 6740 7140 7320 7340 7460 7580 7760 7860 7900 8000 8020 8100 8140 8200 8400 8460
0.62 0.55 1.02 0.6 0.84 3.19 1.14 0.43 0.57 0.5 1.1 0.54 0.68 0.66 0.95 1.06 0.81 1.21
0.51 0.38 0.33 0.08 0.07 0.2 0.15 0.14 0.12 0.15 0.29 0.12 0.42 0.11 0.12 0.07 0.39 0.37
0.26 0.85 1.13 0.2 0.23 2.24 0.66 0.24 0.17 0.09 0.69 0.18 0.27 0.39 0.57 0.6 0.4 0.25
0.48 0.04 0.69 0.64 0.63 0.74 0.62 0.18 0.4 0.12 0.47 0.16 0.75 0.2 0.28 0.17 0.79 0.72
432 436 437 434 432 438 433 433 432 431 435 433 435 434 434 435 429 434
42 155 111 33 27 70 58 56 30 19 63 33 40 59 60 57 49 21
77 7 68 107 75 23 54 42 70 25 43 30 110 30 29 16 98 60
0.66 0.31 0.23 0.29 0.24 0.08 0.19 0.37 0.41 0.64 0.3 0.41 0.61 0.22 0.17 0.11 0.49 0.6
Kharita
TOC: Total Organic Carbon (weight percent (wt%) of the whole rock). S1: vaporized hydrocarbon (mg hydrocarbon/g rock). S2: hydrocarbon potentiality (mg hydrocarbon/g rock). S3: CO2 yield during pyrolysis. Tmax: Temperature at which maximum emission of high temperature (S2). hydrocarbon occurs (deg.°C.). HI: Hydrogen index (mg hydrocarbon/g TOC). OI: Oxygen index (mg CO2/g TOC). PI: Production Index (S1/S1 + S2).
4.1.1. Palynofacies association ‘‘A”: (Ph/AOM/Paly) It includes most of the Kharita and part of the Bahariya formations in both wells. In El Noor well, it covers the interval 8580– 8280 ft. 7880 –7280 ft. 7060–6960 ft. and 6900–6600 ft (Figs. 2 and 4). In South Sallum well, it is recorded at depths ranges of
8800–8160 ft., 7936–7552 ft., 7360–7072 ft., 6880-6816 ft. and 6400–6336 ft (Figs. 3 and 5). This palynofacies type is characterized by high enrichment of the phytoclasts group ranging from (90–100%) of the total kerogen material. It is composed mostly of translucent woody tracheids. The
Please cite this article in press as: N.A. Ela et al., Source rock evaluation of Kharita and Bahariya formations in some wells, North Western Desert, Egypt: Visual palynofacies and organic geochemical approaches, Egypt. J. Petrol. (2017), http://dx.doi.org/10.1016/j.ejpe.2017.07.009
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Fig. 4. Tyson ternary diagram for Kharita samples plot from El Noor well. (adapted after Tyson, 1993 [19]).
Fig. 5. Tyson ternary diagram for Kharita and Bahariya samples plot from. South Sallum well (adapted after Tyson [19]).
phytoclasts in this association are generally well to moderate preserved and with variable sizes and shapes. The amorphous organic matter comes in the next importance, reach to average percentage from (0–10%). The palynomorphs are presented in low frequency (0–5%) (Figs. 2–5, 7 and 8) [21,22]. This characteristics reveals that the main type of kerogen is type III (mainly gas – prone type). 4.1.2. Palynofacies association ‘‘B”: (Ph/Paly/AOM) It covers the interval 8280–7880 ft., 6960–6900 ft., 6500–6430 in El Noor well (Figs. 2 and 4). In the South Sallum well, it is recorded throughout the interval of 8160–7936 ft (Figs. 3 and 5) in the Kharita Formation. In this palynofacies assemblage there is
increase in the palynomorphs group that reaches to (15–55%) represented mainly by terrestrial palynomorphs rather than marine palynomorphs. Phytoclasts ranges (45–85%) with nearly equal amounts of opaque and translucent while AOM is still of low concentration ranging from (0–10%) (Figs. 2–5 and 7), indicates Kerogen Type III, gas-prone type as the phytoclasts are still the dominant palynofacies parameter. 4.1.3. Palynofacies association ‘‘C”: (Ph/AOM/Paly) The described palynofacies covers the interval 6976–6880 ft. and from 6816-6464 ft. in South Sallum well (Figs. 3 and 5). It is characterized by abundance of phytoclasts range from (45–85%)
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Fig. 6. Tyson ternary diagram for Bahariya samples plot from El Noor well. (adapted after Tyson [19]).
which is less in concentration than the phytoclasts recorded in the palynofacies association (A). The AOM and the palynomorphs showed an increasing from the palynofacies association ‘‘A” to be (15–55%) and (10–55%) respectively. Type: III/II kerogen, gasprone type is proposed for this palynofacies assemblage based on the dominance of phytoclasts and AOM (Figs. 3, 5, 7 and 8). 4.1.4. Palynofacies association ‘‘D”: (AOM/Ph/Paly) It covers the interval 6620–6520 ft. in El Noor well (Fig. 5). In South Sallum well it is recorded for 7072–6976 ft (Fig. 6). Remarkable increase appeared in the amount of AOM that ranges from (35–65%), in addition, the phytoclasts are significantly lowered
comparing to the previously recorded palynofacies ‘‘B” with abundant amount of translucent phytoclats over opaque phytoclasts. The amounts of palynomorphs did not change (0–10%), the marine palynomorphs are represented mainly by foraminiferal test lining rather than marine dinocysts (Fig. 7). Type: II kerogen, (oilprone) is suggested for this facies based on the common occurrence of (AOM) and frequent phytoclasts. 4.1.5. Palynofacies association ‘‘E”: (AOM/Ph/Paly) It is recorded in El Noor well through 7280–7080 ft., 6460– 6380 ft (Fig. 8). In South Sallum well, it covers the interval 7552– 7456 ft., 6464–6400 ft. and 6336–6208 ft (Fig. 3). It is characterized
Fig. 7. Microplanktons-spore-pollen ternary diagram for Bahariya samples plot from El Noor and South Sallum wells (adapted after Tyson, [20], Federova [21] and Duringer and Dubinger, [22]).
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Fig. 8. Microplanktons-spore-pollen ternary diagram for Kharita samples plot from El Noor and South Sallum wells (adapted after Tyson, [20], Federova [21] and Duringer and Dubinger, [22]).)
by high enrichment of the amount of amorphous organic matter with average percentage (75–100%) that exceeded the concentration of AOM in the palynofacies association ‘‘D” while the phytoclasts show a remarkable decrease from playnofacies association ‘‘D” to be (0–35%) with palynomorphs content ranges from (0– 10%) (Figs. 2, 3, 5–8). Type II kerogen (oil-prone) is suggested for this facies based on the common occurrence of (AOM) and frequent phytoclasts. 4.2. Spore coloration and thermal maturation The color of fresh spore exines in transmitted light ranges from pale yellow to almost colorless and they changed by time and temperature (e.g., by deep burial or proximity to a lava flow), from yellow, orange to brown, dark brown and finally black [23]. In the present work, simple thin-walled psilate palynomorphs (e.g., Cyathidites australis) were chosen to investigate their exines color using Pearson’s [24] color chart and [25] scale of palynomorph colors to estimate approximately the numerical thermal alteration index (TAI), vitrinite reflectance (Ro%) and organic thermal maturity in the studied wells. The change in color of the recovered spores in the successions of both wells is as follows: 1. The samples from the Kharita Formation contain abundant brown phytoclasts. The color of the Cyathidites australis spore grains are immature dark yellow to orange, which indicating a thermal alteration index (TAI) ranges between 2 and 2 and vitrinite reflectance of 0.5% [24]. 2. The samples from the Bahariya Formation display translucent and brown phytoclasts. The color of the Cyathidites australis spore grains did not change from the older samples from Kharita Formation. The color ranged between immature dark yellow and orange, which indicates a thermal alteration index between 2 and 2 and vitrinite reflectance of 0.5% [24].
4.3. Hydrocarbon generation potentiality depending on the palynofacies analysis and spore coloration Depending on the palynofacies analysis, the hydrocarbon generation potentiality is poor in both of these formations (kerogen types range between gas prone III and oil prone II) and they are immature to yield any hydrocarbons. The previous studies in the Western Desert confirm the present conclusion, where the samples from Bahariya and Kharita formations were immature and of poor hydrocarbon generation potentiality [2,5,8–10]. The integrating of the results between these works perhaps means that the conditions during the deposition of both studied formations were uniform through at least the northern part of the Western Desert. This study suggests the increasing of the marine influence in the north, where more AOM accumulations are expected although it depends on other paleoenvironmental conditions (like oxygen content). The higher potentiality to be source rocks or to generate hydrocarbons in Bahariya and Kharita formations should be in the deeper offshore region to the north of the location of the present studied area. 4.4. Organic geochemical analysis It is based on the integration between the palynofacies assessment of the kerogen type and organic geochemical analysis by using the Rock-Eval-6 pyrolysis analyzer. This integration allows simultaneous visual and quantitative control on the hydrocarbon generation potentiality. [26–28]. 4.4.1. Organic richness and hydrocarbon potentiality The organic richness of any source rock is determined by the total organic carbon ‘‘TOC” in the whole rock and pyrolysis derived ‘‘S2”of the rock samples [28]. Eighteen representative ditch samples from El Noor Well were analyzed by Rock Eval-6 to obtain the geochemical pyrolysis data represented in (Table 3).
Please cite this article in press as: N.A. Ela et al., Source rock evaluation of Kharita and Bahariya formations in some wells, North Western Desert, Egypt: Visual palynofacies and organic geochemical approaches, Egypt. J. Petrol. (2017), http://dx.doi.org/10.1016/j.ejpe.2017.07.009
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Fig. 9. Rock Eval pyrolysis data of El Noor well. (a) TOC (b) S2 (C) Tmax.
In the study samples of Kharita Formation the TOC values range from 0.50 to 1.21 wt% (Table 3), which represents Fair to good organic richness (Fig. 9). The S2 values ranges from 0.09 to 0.69 mg./g. which represent poor generating source, (Fig. 9b). In the Bahariya Formation, the total organic carbon content ‘‘TOC” values ranging from 0.43 wt% to 3.19 wt% which represent fair to good total organic carbon content with one sample lies in the very good zone (Fig. 9a). The generating source potential ‘‘S2” ranges from 0.17 to 2.24 mg/g (Table 3), indicating poor S2 content (Fig. 9b).
4.4.2. Genetic type of organic matter The type of organic matter completes the organic richness in evaluating the generating potential of a source rock. Its origin may be terrestrial, as in case of peats, lignites and coal seams or aquatic, as in case of animal and fungal remains, or mixture of both, as in case of many oil shales and presumed oil-source rocks [20]. In the present study we use the pyrolysis method, the hydrogen index ‘‘HI” values of the Kharita Formation in El Noor well ranges from 19 to 63 (mg./g.) and the ‘‘OI’ values ranges from 16 to 110 (mg./g.) respectively, while Bahariya Formation in El Noor well
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inated with terrestrial phytoclastic materials in both studied formations (Figs. 2–8) [30]. 4.5. Organic thermal maturation In the present study various parameters used to estimate source rock maturation. as vitrinite reflectance (Ro), the temperature at which the kerogen yields maximum hydrocarbons (Tmax.) [31]. Espitalie et al. [32] and Peters [33] reported that oil generation from source rocks began at ‘‘Tmax.” 435–465 °C, vitrinite reflectance ‘‘Ro%” between 0.5% and 1.35% and production index ‘‘Pl” between 0.1 and 0.4. ‘‘Tmax.” has a value less than 435 °C, ‘‘Ro”% less than 0.5% and ‘‘Pl” less than 0.1; represents organic matters in the immature stage. Gas generation from source rocks began at ‘‘Tmax.” 470 °C, vitrinite reflectance is more than 1.35% and production index ‘‘Pl” more than 0.4. In the study samples the Tmax.values for the Kharita Formation ranges from 429 to 435 °C (Table 3) which represents immature to marginally mature samples to yield hydrocarbons (Fig. 9c), the Tmax. values for Bahariya Formation ranges from 432 to 438 °C (Table 3) which represent immature to marginally mature rock (Fig. 9c), and the expected hydrocarbon to be generated from the samples in case of maturation can be obtained by plotting the TOC vs. HI [26].The study samples in case of maturation are capable of generating mainly gas hydrocarbon (Fig. 11) [34] Fig. 10. Modified Van Krevelen type diagram showing kerogen type of the studied. samples of El Noor well (after Waples [28]).
5. Conclusions The present palynofacies analysis carried on the subsurface Albian – Cenomanian Kharita and Bahariya formations, encountered in El-Noor and South Sallum wells are illustrating potential results concerning with their depositional paleoenvironments and source rock probability in the northern Western Desert. Five palynofacies associations were recognized. Kharita Formation took place mainly in a steady and a relatively stable deltaic to marginal environment. The marine influence became more common in the upper part of Bahariya Formation showing the exceptional high hydrocarbon potential. Such rising in the marine influence indicates marine transgression by the end of the early Cenomanian time. Kharita Formation indicates possibility to gas-prone kerogen type III and IV, while most of Bahariya Formation points to more promising gas-prone kerogen type III. This study demonstrates poor to fair gas-prone source rock potential within the Albian Cenomanian section. Thermally, the color of the spore grains Cyathidites australis in Kharita and Bahariya formations illustrates immature dark yellow to orange, according to Thermal Maturation Index (TAI). Acknowledgment
Fig. 11. Source Rock characterization using plot of HI vs. TOC. (Jackson et al., 1985) [34].
range from 27 to 155 (mg./g.) and oxygen index ‘‘Ol” from 7 to 107 (mg./g.), (Table 3). These data reflect that the main expected kerogen type is type (III) for producing (gas) as shown in the modified Van Krevelen diagram (Fig. 10). This conclusion reflects that the main organic source material is terrestrial organic matter [29]. It is well integrated and supported with the palynofacies examinations, which revealed almost the same kerogen types that are dom-
The authors are indebted to the authority of EGPC for providing the samples for this study, and are grateful to the Egyptian Petroleum Research Institute (EPRI) for supporting the staff and the micropaleontology and organic geochemistry laboratory facilities. We are very particularly grateful for helpful and constructive comments provided by the reviewers. References [1] M.K. Ayouty, Petroleum geology, in: R. Said (Ed.), The Geology of Egypt, Balkema, 1990, p. 567. [2] S.Y. El Beialy, Aptian to Cenomanian palynomorphs from the Qarun 2-1 borehole, Western Desert, Egypt, Qatar Univ. Sci. J. 13 (1) (1993) 152–160. [3] M.I.A. Ibrahim, E. Schrank, Palynological studies on the Late Jurassic-Early Cretaceous of the Kahraman-1 well, northern Western Desert, Egypt, Actes Colloques Angers 1994 (1996), 1996-629. [4] M.I.A. Ibrahim, N.M. Aboul Ela, S.E. Kholeif, Palaeoecology, palynofacies, thermal maturation and hydrocarbon source-rock potential of the Jurassic–
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Source rock evaluation of Kharita and Bahariya formations in some wells, North Western Desert, Egypt: Visual palynofacies and organic geochemical approaches Nabil Aboul Ela a, Sameh S. Tahoun a, Tarek Fouad b, Doaa A. Mousa b,⇑, Rehab Saleh b a b
Geology Department, Faculty of Science, Cairo University, P.O. Box 12613, Giza, Egypt Exploration Department, Egyptian Petroleum Research Institute, 1 Ahmed El-Zomor Street, El-Zohour Region, Nasr City, Cairo 11727, Egypt
a r t i c l e
i n f o
Article history: Received 2 April 2017 Revised 14 July 2017 Accepted 26 July 2017 Available online xxxx Keywords: Palynofacies Rock eval pyrolysis Bahariya formation Kharita formation North Western Desert Egypt
a b s t r a c t Palynofacies analyses were applied on ninety-one samples from the subsurface Albian – Cenomanian succession represented by Kharita and Bahariya formations, encountered in El-Noor, and South Sallum wells, located in the North Western Desert, Egypt, to visually characterize the content of dispersed organic matter, as well as, organic geochemical characterization to reveal the depositional paleoenvironments and source rock potentiality. The result recognized of five palynofacies associations in the studied interval. The deposition of Kharita Formation took place mainly in a steady and a relatively stable deltaic to marginal environment continued as well in the lower part of Bahariya Formation with minor changes. The marine influence became more common in the upper part of Bahariya Formation showing the exceptional high hydrocarbon potential recorded in the studied interval. This indicates marine transgression by the end of the early Cenomanian (Upper Bahariya) age. Samples from the Kharita Formation contain abundant brown phytoclasts which suggest gas-prone kerogen type III and IV. While Bahariya Formation includes translucent, brown cuticles and woody tracheid phytoclasts pointing to more promising gasprone kerogen type III. The organic geochemical analysis shows poor to fair gas-prone source rock potential within the study section., Thermally, the color of the spore grains in Kharita and Bahariya formations show that dark yellow to orange, indicates immature besides their general little poor hydrocarbon generation potentiality. Ó 2017 Egyptian Petroleum Research Institute. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction The studied wells El-Noor, and South Sallum are locates in the northern Western Desert between latitude (31° 190 36.91 6700 N, 26° 040 19.25 7700 E), located in the North Western Desert of Egypt (Fig. 1). The Albian- Cenomanian intervals which include Kharita and Bahariya formations are the most important rock successions in the subsurface of the Western Desert of Egypt. These two formations confine the essential petroleum deposits and represent the central target for exploration [1]. In the recent years, many studies were conducted to investigate the paleoenvironment of deposition
Peer review under responsibility of Egyptian Petroleum Research Institute. ⇑ Correspondence to: D.A. Mousa. E-mail addresses: [email protected] (N.A. Ela), [email protected] (S.S. Tahoun), [email protected] (T. Fouad), [email protected] (D.A. Mousa), [email protected] (R. Saleh).
during the Albian Cenomanian with special focus on palynofacies as a reliable tool for analysis [2–10]. Furthermore, the geochemical investigations of Kharita and Bahariya formations in the North Western Desert discussed by many authors [11–16], among of them recognized that the Kharita and Bahariya formations are ranges from immature to mature source rocks. The current investigations represent the additional contribution to the line concerning the applications of palynofacies in outlining the paleoenvironmental conditions and source rock evaluations with compatible results from organic geochemical analysis. This paper is focusing on the palynofacies and the geochemical analysis on the relatively closely spaced El-Noor and South Sallum wells. (Fig. 1). The main target of the present study is the identification of the palynofacies types, interpreting the depositional paleoenvironments, estimating the thermal maturation of the studied formations using the spore coloration. Finally, comprehensive source rock evaluation by integrating the results from palynofacies and geochemical analyses.
http://dx.doi.org/10.1016/j.ejpe.2017.07.009 1110-0621/Ó 2017 Egyptian Petroleum Research Institute. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article in press as: N.A. Ela et al., Source rock evaluation of Kharita and Bahariya formations in some wells, North Western Desert, Egypt: Visual palynofacies and organic geochemical approaches, Egypt. J. Petrol. (2017), http://dx.doi.org/10.1016/j.ejpe.2017.07.009
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2.1. Kharita formation It overlies conformably with the Dahab Formation and underlies the Bahariya Formation. It is composed mainly of sandstone that shows fining upward sequences, with shale and thin limestone streaks confined in certain areas. Thick sandstone units with minor shale intercalations characterize the lower part of this formation [17–18]. In El-Noor well, the depth interval of the Kharita Formation is between 7790–8590 ft (Fig. 2). This formation consists mainly of colorless, fine to coarse grained, poorly sorted and subrounded sandstone. In South Sallum well, the depth interval of the Kharita Formation is between 7552–8800 ft (Fig. 3). The lithological composition of this formation is colorless, fine to coarse grained, poorly sorted and subrounded sandstone.
2.2. Bahariya formation
Fig. 1. Location map of the studied El – Noor and South Sallum wells.
2. Lithostratigraphy The lithologies, unit thicknesses, and tops of Kharita and Bahariya formations in the studied interval in El Noor and south Sallum wells are discussed below.
It rests conformably or sometimes unconformably on the Kharita Formation and is overlain conformably by Abu-Roash Formation. It dates as late Albian – early Cenomanian and deposited under fluvial to shallow marine environment [17–18]. The described formation is dominated by near shore marine finegrained sandstone, interbeded with shale and siltstones. The basal part of the formation usually includes massive sands, but these sands are more shaley and less uniform than the sands of the underlying Kharita and it is dated as of Cenomanian age. In El-Noor well the depth interval of the Bahariya Formation is
Fig. 2. Lithostratigraphic colum, locations of the studied samples and palynofacies percentage vertical distribution of El Noor well.
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Fig. 3. Lithostratigraphic colum, locations of the studied samples and palynofacies percentage vertical distribution of of South Sallum well.
between 6350–7790 ft (Fig. 2). This formation is composed of greenish to white greenish, fine to very fine sandstone and moderately sorted, with glauconite cement. Shale in this formation is greenish grey to dark grey and firm. In South Sallum well the depth interval of the Bahariya Formation is between 6200–7552 ft (Fig. 3). it consists of interbeded sandstone, which is colorless, yellowish white, and shale, which is grey to greenish grey and flacky. The sandstone is fine to coarse grained, angular to subrounded and poorly sorted. In the upper part, this formation composed of marly limestone. 3. Material and methods Sixty-two (62) representative samples were prepared from El-Noor well, and twenty-nine (29) samples picked from South Sallum well in order to make qualitative as well as quantitative palynofacies analyses for the recovered particulate organic matter (POM), to delineate the different palynofacies assemblages and kerogen types variation throughout the studied formations in the studied intervals.
2. Eighteen (18) representative samples from El Noor Well were analyzed by Rock Eval-6 analyser to obtain the Organic geochemical data represented in Table 3. About 60 mg of washed, dry and fine grained sample is loaded in the crucible of the Rock Eval-6, the programmed run in the Rock Eval-6 to obtain the main screen analysis data for the studied samples, according to a programmed temperature pattern. The released hydrocarbons are monitored by a Flame Ionization Detector (FID), forming the so-called peaks S1 (thermo-vaporized free hydrocarbons) and S2 (hydrocarbons from cracking of organic matter). In addition, CO and CO2 released during pyrolysis can be monitored in real time by means of an Infrared (IR) cell. The method can be completed by oxidation of the rock sample according to a programmed temperature pattern. This complementary stage allows determination of Total Organic Carbon and Mineral Carbon content of the concerned samples. All these analyses were carried out in the Egyptian Petroleum Research Institute [EPRI].
4. Results and discussion 1. Extraction procedures involving dilute HCl and HF, wet sieving using 10m polyester sieves, and mounting by using UV liquid media. Quantitative analysis of the overall kerogen composition was carried out on sieved, unoxidized material. At least two slides of each sample were studied. Each slide was counted for its (POM) content, in which the first 500 particles were counted in terms of abundant (>35%), frequent (16–35%), common (5–15%) and rare (<5%) (Tables 1 and 2).
4.1. Palynofacies analysis The relative variations in abundances of the different palynofacies classes reveal the depositional environments. In addition the visual examination of the palynofacies indicates the hydrocarbon generation potentiality of the source rocks. Palynofacies is classified into three main classes, which are recognized using the
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N.A. Ela et al. / Egyptian Journal of Petroleum xxx (2017) xxx–xxx
translucent, dispersed particles of plant-derived kerogen other than palynomorphs. Tables 1 and 2 show the quantitative distribution of the various particulate organic matters (POM) recorded from El Noor and South Sallum wells respectively. These palynofacies assemblage are described as the following:
classification scheme of [19–20] Palynomorphs is classified into terrestrial (sporomorphs) or marine (dinoflagellates – foraminifera test linings). The Amorphous organic matter (AOM)) refers to all structureless, fluffy dispersed particles of kerogen, whether of marine or non-marine origin. It is derived from phytoplanktons or degradation of bacteria. Phytoclasts are structured, opaque or
Table 1 Quantitative distribution of particulate organic matter in El Noor well. Depth Pollen
Spore
Terr. Palynomorphs
Spore/ pollen
Terrestrial Dinoflagellate palynomorphs
Marine palynomorphs
Marine/ Terrestrial
Op. lath.
Palynomophs
WP
AOM
F.T.L
Phytoclast
6380 6420 6480 6520 6560 6600 6640 6680 6700 6740 6780 6820 6840 6880 6920 6960 7020 7060 7100 7140 7180 7220 7260 7300 7340 7380 7420 7460 7500 7560 7600 7640 7680 7720 7760 7800 7840 7880 7920 7980 8020 8040 8100 8140 8180 8220 8260 8300 8340 8380 8420 8460 8500 8540 8580 8600 8640 8680 8720 8760 8800 8840
2.22 2.11 0.20 1.06 0.15 2.77 1.88 4.59 1.57 1.46 2.78 2.15 1.34 1.41 3.40 1.43 1.78 3.28 1.32 2.46 2.90 1.65 2.13 4.31 4.44 1.41 0.88 1.46 1.70 5.96 2.75 1.66 2.69 0.92 1.50 1.09 0.84 0.58 0.62 1.46 0.63 0.64 1.11 0.84 0.65 0.56 2.30 0.28 0.58 0.66 0.47 0.39 0.15 0.42 0.94 1.06 1.16 0.63 0.32 0.23 0.45 0.46
3.91 3.24 2.78 5.75 0.98 5.70 2.78 5.31 1.90 1.74 3.59 2.70 2.05 1.80 5.71 2.83 2.76 4.35 3.45 5.07 6.75 2.51 3.23 8.37 6.23 1.94 1.21 1.90 2.00 7.38 3.84 2.97 3.83 1.51 2.49 1.60 1.07 0.76 0.78 2.62 0.79 0.90 1.84 1.55 1.03 0.89 3.63 0.38 0.95 1.05 0.73 0.50 0.21 0.61 1.25 1.42 1.57 0.68 0.39 0.29 0.65 0.63
2.09 1.91 0.08 0.25 0.18 0.97 2.09 9.60 5.61 5.94 4.07 4.76 2.00 3.95 2.02 1.12 2.08 4.10 0.66 1.01 0.85 2.13 2.20 1.46 3.47 2.78 2.83 3.77 6.19 5.30 2.85 1.29 2.94 1.61 1.66 2.26 3.99 3.45 4.17 1.86 4.84 2.66 1.59 1.21 1.78 1.76 2.19 2.80 1.61 1.78 1.82 3.56 2.38 2.30 3.28 3.40 3.40 15.14 4.33 3.75 2.39 2.97
3.28 3.21 2.78 5.40 0.98 5.63 2.77 5.06 1.85 1.71 3.46 2.60 2.01 1.76 5.09 2.71 2.63 4.08 3.32 4.89 6.32 2.43 3.10 7.26 5.72 1.92 1.19 1.85 1.98 7.08 3.72 2.94 3.60 1.49 2.40 1.57 1.06 0.75 0.77 2.25 0.77 0.89 1.81 1.53 1.02 0.87 3.35 0.37 0.94 1.03 0.72 0.50 0.21 0.61 1.23 1.37 1.50 0.68 0.39 0.29 0.64 0.62
4.40 0.66 0.13 0.75 0.02 2.83 0.16 0.59 0.06 0.05 0.15 0.13 0.06 0.05 0.67 0.13 0.15 0.44 0.16 0.33 0.49 0.12 0.23 1.37 0.69 0.07 0.03 0.06 0.05 1.14 0.30 0.14 0.40 0.04 0.12 0.05 0.02 0.01 0.02 0.39 0.02 0.02 0.05 0.03 0.03 0.02 0.31 0.00 0.02 0.02 0.01 0.01 0.00 0.01 0.03 0.06 0.11 0.01 0.00 0.00 0.01 0.01
1.34 0.21 0.05 0.14 0.02 0.50 0.06 0.12 0.03 0.03 0.04 0.05 0.03 0.03 0.13 0.05 0.06 0.11 0.05 0.07 0.08 0.05 0.07 0.19 0.12 0.04 0.02 0.03 0.03 0.16 0.08 0.05 0.11 0.03 0.05 0.03 0.02 0.02 0.02 0.17 0.03 0.02 0.03 0.02 0.03 0.02 0.09 0.01 0.02 0.02 0.01 0.01 0.00 0.01 0.03 0.05 0.08 0.02 0.01 0.01 0.01 0.01
11.14 67.92 42.63 40.61 20.63 14.17 63.74 52.55 47.04 40.04 64.92 48.54 37.76 43.64 23.06 32.89 39.36 37.72 38.38 59.44 27.79 37.57 45.79 35.65 34.45 45.24 44.99 36.18 42.68 49.95 57.59 56.92 50.34 57.49 39.61 40.18 48.28 84.02 65.21 63.36 68.48 74.77 54.64 61.45 58.70 67.14 56.62 61.77 70.14 69.62 68.82 39.06 58.60 56.67 57.73 51.64 54.44 69.34 69.55 59.02 64.94 66.53
7.68 3.87 2.91 6.14 1.00 8.46 2.93 5.66 1.91 1.76 3.61 2.73 2.06 1.82 5.76 2.84 2.78 4.52 3.48 5.22 6.81 2.54 3.33 8.64 6.41 1.98 1.22 1.91 2.03 8.22 4.02 3.08 4.00 1.53 2.52 1.62 1.08 0.76 0.78 2.64 0.79 0.90 1.86 1.56 1.04 0.89 3.66 0.38 0.96 1.05 0.73 0.51 0.21 0.62 1.26 1.43 1.61 0.69 0.39 0.29 0.65 0.63
30.38 19.86 51.67 35.44 32.58 27.56 28.94 36.31 46.46 44.86 25.57 43.09 55.46 49.38 67.17 53.69 49.50 49.51 46.28 25.70 50.68 49.32 42.27 34.54 39.62 46.43 51.17 60.30 48.78 28.43 32.52 32.31 38.63 29.97 38.45 44.34 40.04 10.96 28.77 32.10 29.85 22.11 38.73 27.88 34.00 30.20 30.42 32.70 26.14 26.58 26.28 40.28 38.43 38.81 33.22 43.44 43.15 25.86 25.93 36.64 32.90 31.38
50.80 8.34 2.80 17.81 45.79 49.80 4.40 5.47 4.59 13.35 5.90 5.64 4.72 5.17 4.01 10.59 8.35 8.25 11.85 9.64 14.71 10.57 8.61 21.17 19.52 6.35 2.62 1.61 6.50 13.40 5.88 7.69 7.02 11.01 19.42 13.86 10.60 4.26 5.23 1.90 0.88 2.21 4.77 9.10 6.26 1.78 9.30 5.15 2.76 2.74 4.17 20.14 2.76 3.90 7.79 3.48 0.81 4.11 4.13 4.05 1.52 1.46
3.77 0.63 0.13 0.39 0.01 2.77 0.15 0.34 0.01 0.02 0.01 0.03 0.02 0.02 0.06 0.01 0.02 0.17 0.04 0.15 0.06 0.04 0.09 0.27 0.19 0.04 0.01 0.01 0.03 0.84 0.17 0.11 0.17 0.02 0.04 0.02 0.01 0.01 0.01 0.02 0.00 0.00 0.02 0.02 0.01 0.00 0.04 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.04 0.00 0.00 0.00 0.00 0.00
41.52 87.79 94.29 76.05 53.21 41.73 92.67 88.87 93.50 84.89 90.49 91.63 93.22 93.01 90.23 86.58 88.87 87.23 84.67 85.14 78.47 86.89 88.06 70.19 74.07 91.67 96.16 96.48 91.46 78.38 90.11 89.23 88.98 87.46 78.06 84.53 88.32 94.98 93.98 95.46 98.33 96.88 93.37 89.33 92.70 97.34 87.04 94.47 96.28 96.20 95.10 79.35 97.03 95.48 90.95 95.08 97.58 95.20 95.48 95.66 97.84 97.91
1.06 1.10 2.57 4.33 0.83 2.87 0.90 0.48 0.28 0.25 0.68 0.45 0.67 0.36 1.69 1.28 0.85 0.80 1.99 2.43 3.42 0.78 0.97 2.95 1.28 0.51 0.31 0.39 0.28 1.12 0.97 1.28 0.92 0.57 0.90 0.48 0.21 0.17 0.15 0.79 0.13 0.24 0.70 0.69 0.37 0.31 1.05 0.10 0.36 0.37 0.26 0.11 0.06 0.18 0.29 0.31 0.34 0.04 0.07 0.06 0.19 0.16
0.63 0.03 0.00 0.36 0.01 0.07 0.01 0.25 0.05 0.04 0.13 0.10 0.04 0.03 0.61 0.12 0.13 0.27 0.13 0.18 0.43 0.08 0.13 1.11 0.51 0.03 0.02 0.05 0.02 0.30 0.12 0.04 0.22 0.03 0.09 0.03 0.01 0.01 0.01 0.38 0.02 0.02 0.03 0.01 0.01 0.02 0.28 0.00 0.01 0.02 0.01 0.00 0.00 0.00 0.02 0.05 0.07 0.01 0.00 0.00 0.00 0.01
The abbreviations used in these tables are (POM) Particulate Organic Matter – (Tr.) Terrestrial Palynomorph – (Mr.) Marine Palynomorph – (Tr.O) Translucent Organic Matter – (AOM) Amorphous Organic Matter – (Pl.) Pollen – (Sp.) Spore – (Dino.)Dinoflagellate – (OP.) Opaque Organic Matter – (Ph)Phytoclasts – (FTL) Foraminiferal Test Lining - (Paly.) Palynomorph.
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N.A. Ela et al. / Egyptian Journal of Petroleum xxx (2017) xxx–xxx Table 2 Quantitative distribution of particulate organic matter in South Sallum well. Depth
Pollen
Spore
Spore/ pollen
Terrestrial palynomorphs
Dinoflagellate
F.T.L
Marine palynomorphs
Marine/ Terrestrial
Palynomorphs
Op.lath.
WP
Phytoclast
AOM
6208 6272 6336 6400 6464 6528 6592 6656 6752 6816 6880 6976 7072 7168 7264 7360 7456 7552 7648 7744 7840 7936 8032 8160 8245 8352 8400 8544 8800
0.00 0.18 0.19 0.95 2.15 1.21 1.59 4.70 6.98 5.12 0.34 7.22 0.19 1.21 2.21 2.21 0.00 1.59 0.93 2.50 0.63 2.05 1.85 2.21 1.21 1.10 0.51 0.93 0.71
0.19 0.35 1.69 0.00 2.15 3.98 4.78 5.80 7.61 4.33 3.02 6.19 1.69 3.98 4.71 4.71 0.19 4.78 2.48 3.39 0.95 3.55 12.00 4.71 5.71 7.34 3.00 1.28 2.30
0.00 2.00 9.00 0.00 1.00 3.29 3.00 1.23 1.09 0.85 9.00 0.86 9.00 3.29 2.13 2.13
0.19 0.53 1.88 0.95 4.31 5.19 6.38 10.50 14.59 9.45 3.36 13.40 1.88 5.19 6.92 6.92 0.19 6.38 3.41 5.89 1.58 5.59 13.85 6.92 6.92 8.44 3.50 2.21 3.00
0.93 0.89 0.75 0.95 2.15 3.11 0.48 0.94 1.48 1.57 0.17 1.55 0.75 3.11 0.59 0.59 0.93 0.48 0.16 0.00 0.16 0.00 0.62 0.59 0.69 0.73 0.27 0.16 0.18
0.56 0.89 5.64 2.13 4.31 0.35 0.16 0.00 1.27 0.39 0.17 0.00 5.64 0.35 0.29 0.29 0.56 0.16 0.16 0.18 0.79 0.00 0.00 0.29 0.29 0.18 0.00 0.16 0.00
1.49 1.77 6.39 3.07 6.46 3.46 0.64 0.94 2.75 1.97 0.34 1.55 6.39 3.46 0.88 0.88 1.49 0.64 0.31 0.18 0.95 0.00 0.62 0.88 0.99 0.92 0.27 0.31 0.18
8.00 3.33 3.40 3.25 1.50 0.67 0.10 0.09 0.19 0.21 0.10 0.12 3.40 0.67 0.13 0.13 8.00 0.10 0.09 0.03 0.60 0.00 0.04 0.13 0.14 0.11 0.08 0.14 0.06
1.68 2.30 8.27 4.02 10.77 8.65 7.02 11.44 17.34 11.42 3.69 14.95 8.27 8.65 7.81 7.81 1.68 7.02 3.72 6.07 2.54 5.59 14.46 7.81 7.91 9.36 3.77 2.52 3.18
4.47 8.87 16.92 41.13 10.15 35.29 34.77 31.03 30.44 36.61 44.30 34.02 16.92 35.29 40.65 40.65 4.47 34.77 43.72 37.50 44.69 44.20 34.15 40.65 43.55 37.43 43.40 43.72 42.40
5.59 10.11 19.36 42.08 14.46 42.39 40.03 37.77 39.53 42.52 47.48 41.75 19.36 42.39 45.95 45.95 5.59 40.03 46.36 40.89 45.80 47.75 46.77 45.95 42.55 45.50 44.88 46.36 44.88
10.06 18.97 36.28 83.22 24.62 77.68 74.80 68.81 69.98 79.13 91.78 75.77 36.28 77.68 86.60 86.60 10.06 74.80 90.08 78.39 90.49 91.95 80.92 86.60 86.10 82.94 88.28 90.08 87.28
88.27 78.72 55.26 12.77 64.62 13.49 18.18 19.75 12.68 9.45 4.03 9.28 55.26 13.49 5.30 5.30 88.27 18.18 5.58 15.00 6.66 2.46 4.62 5.30 5.30 7.71 9.54 7.58 9.54
3.00 2.67 1.36 1.50 1.73 6.50 2.13 4.72 6.67 5.91 1.38 3.25
The abbreviations used in these tables are (POM) Particulate Organic Matter – (Tr.) Terrestrial Palynomorph – (Mr.) Marine Palynomorph – (Tr.O) Translucent Organic Matter – (AOM) Amorphous Organic Matter – (Pl.) Pollen – (Sp.) Spore – (Dino.)Dinoflagellate – (OP.) Opaque Organic Matter – (Ph)Phytoclasts – (FTL) Foraminiferal Test Lining - (Paly.) Palynomorph.
Table 3 Rock Eval-6 pyrolysis data for the geochemical analysis of El Noor well. Formation
Depth
TOC Wt%
S1 mg./g.
S2 mg/g
S3 mg/g
T max
HI
OI
PI
Bahariya
6560 6620 6740 7140 7320 7340 7460 7580 7760 7860 7900 8000 8020 8100 8140 8200 8400 8460
0.62 0.55 1.02 0.6 0.84 3.19 1.14 0.43 0.57 0.5 1.1 0.54 0.68 0.66 0.95 1.06 0.81 1.21
0.51 0.38 0.33 0.08 0.07 0.2 0.15 0.14 0.12 0.15 0.29 0.12 0.42 0.11 0.12 0.07 0.39 0.37
0.26 0.85 1.13 0.2 0.23 2.24 0.66 0.24 0.17 0.09 0.69 0.18 0.27 0.39 0.57 0.6 0.4 0.25
0.48 0.04 0.69 0.64 0.63 0.74 0.62 0.18 0.4 0.12 0.47 0.16 0.75 0.2 0.28 0.17 0.79 0.72
432 436 437 434 432 438 433 433 432 431 435 433 435 434 434 435 429 434
42 155 111 33 27 70 58 56 30 19 63 33 40 59 60 57 49 21
77 7 68 107 75 23 54 42 70 25 43 30 110 30 29 16 98 60
0.66 0.31 0.23 0.29 0.24 0.08 0.19 0.37 0.41 0.64 0.3 0.41 0.61 0.22 0.17 0.11 0.49 0.6
Kharita
TOC: Total Organic Carbon (weight percent (wt%) of the whole rock). S1: vaporized hydrocarbon (mg hydrocarbon/g rock). S2: hydrocarbon potentiality (mg hydrocarbon/g rock). S3: CO2 yield during pyrolysis. Tmax: Temperature at which maximum emission of high temperature (S2). hydrocarbon occurs (deg.°C.). HI: Hydrogen index (mg hydrocarbon/g TOC). OI: Oxygen index (mg CO2/g TOC). PI: Production Index (S1/S1 + S2).
4.1.1. Palynofacies association ‘‘A”: (Ph/AOM/Paly) It includes most of the Kharita and part of the Bahariya formations in both wells. In El Noor well, it covers the interval 8580– 8280 ft. 7880 –7280 ft. 7060–6960 ft. and 6900–6600 ft (Figs. 2 and 4). In South Sallum well, it is recorded at depths ranges of
8800–8160 ft., 7936–7552 ft., 7360–7072 ft., 6880-6816 ft. and 6400–6336 ft (Figs. 3 and 5). This palynofacies type is characterized by high enrichment of the phytoclasts group ranging from (90–100%) of the total kerogen material. It is composed mostly of translucent woody tracheids. The
Please cite this article in press as: N.A. Ela et al., Source rock evaluation of Kharita and Bahariya formations in some wells, North Western Desert, Egypt: Visual palynofacies and organic geochemical approaches, Egypt. J. Petrol. (2017), http://dx.doi.org/10.1016/j.ejpe.2017.07.009
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N.A. Ela et al. / Egyptian Journal of Petroleum xxx (2017) xxx–xxx
Fig. 4. Tyson ternary diagram for Kharita samples plot from El Noor well. (adapted after Tyson, 1993 [19]).
Fig. 5. Tyson ternary diagram for Kharita and Bahariya samples plot from. South Sallum well (adapted after Tyson [19]).
phytoclasts in this association are generally well to moderate preserved and with variable sizes and shapes. The amorphous organic matter comes in the next importance, reach to average percentage from (0–10%). The palynomorphs are presented in low frequency (0–5%) (Figs. 2–5, 7 and 8) [21,22]. This characteristics reveals that the main type of kerogen is type III (mainly gas – prone type). 4.1.2. Palynofacies association ‘‘B”: (Ph/Paly/AOM) It covers the interval 8280–7880 ft., 6960–6900 ft., 6500–6430 in El Noor well (Figs. 2 and 4). In the South Sallum well, it is recorded throughout the interval of 8160–7936 ft (Figs. 3 and 5) in the Kharita Formation. In this palynofacies assemblage there is
increase in the palynomorphs group that reaches to (15–55%) represented mainly by terrestrial palynomorphs rather than marine palynomorphs. Phytoclasts ranges (45–85%) with nearly equal amounts of opaque and translucent while AOM is still of low concentration ranging from (0–10%) (Figs. 2–5 and 7), indicates Kerogen Type III, gas-prone type as the phytoclasts are still the dominant palynofacies parameter. 4.1.3. Palynofacies association ‘‘C”: (Ph/AOM/Paly) The described palynofacies covers the interval 6976–6880 ft. and from 6816-6464 ft. in South Sallum well (Figs. 3 and 5). It is characterized by abundance of phytoclasts range from (45–85%)
Please cite this article in press as: N.A. Ela et al., Source rock evaluation of Kharita and Bahariya formations in some wells, North Western Desert, Egypt: Visual palynofacies and organic geochemical approaches, Egypt. J. Petrol. (2017), http://dx.doi.org/10.1016/j.ejpe.2017.07.009
N.A. Ela et al. / Egyptian Journal of Petroleum xxx (2017) xxx–xxx
7
Fig. 6. Tyson ternary diagram for Bahariya samples plot from El Noor well. (adapted after Tyson [19]).
which is less in concentration than the phytoclasts recorded in the palynofacies association (A). The AOM and the palynomorphs showed an increasing from the palynofacies association ‘‘A” to be (15–55%) and (10–55%) respectively. Type: III/II kerogen, gasprone type is proposed for this palynofacies assemblage based on the dominance of phytoclasts and AOM (Figs. 3, 5, 7 and 8). 4.1.4. Palynofacies association ‘‘D”: (AOM/Ph/Paly) It covers the interval 6620–6520 ft. in El Noor well (Fig. 5). In South Sallum well it is recorded for 7072–6976 ft (Fig. 6). Remarkable increase appeared in the amount of AOM that ranges from (35–65%), in addition, the phytoclasts are significantly lowered
comparing to the previously recorded palynofacies ‘‘B” with abundant amount of translucent phytoclats over opaque phytoclasts. The amounts of palynomorphs did not change (0–10%), the marine palynomorphs are represented mainly by foraminiferal test lining rather than marine dinocysts (Fig. 7). Type: II kerogen, (oilprone) is suggested for this facies based on the common occurrence of (AOM) and frequent phytoclasts. 4.1.5. Palynofacies association ‘‘E”: (AOM/Ph/Paly) It is recorded in El Noor well through 7280–7080 ft., 6460– 6380 ft (Fig. 8). In South Sallum well, it covers the interval 7552– 7456 ft., 6464–6400 ft. and 6336–6208 ft (Fig. 3). It is characterized
Fig. 7. Microplanktons-spore-pollen ternary diagram for Bahariya samples plot from El Noor and South Sallum wells (adapted after Tyson, [20], Federova [21] and Duringer and Dubinger, [22]).
Please cite this article in press as: N.A. Ela et al., Source rock evaluation of Kharita and Bahariya formations in some wells, North Western Desert, Egypt: Visual palynofacies and organic geochemical approaches, Egypt. J. Petrol. (2017), http://dx.doi.org/10.1016/j.ejpe.2017.07.009
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N.A. Ela et al. / Egyptian Journal of Petroleum xxx (2017) xxx–xxx
Fig. 8. Microplanktons-spore-pollen ternary diagram for Kharita samples plot from El Noor and South Sallum wells (adapted after Tyson, [20], Federova [21] and Duringer and Dubinger, [22]).)
by high enrichment of the amount of amorphous organic matter with average percentage (75–100%) that exceeded the concentration of AOM in the palynofacies association ‘‘D” while the phytoclasts show a remarkable decrease from playnofacies association ‘‘D” to be (0–35%) with palynomorphs content ranges from (0– 10%) (Figs. 2, 3, 5–8). Type II kerogen (oil-prone) is suggested for this facies based on the common occurrence of (AOM) and frequent phytoclasts. 4.2. Spore coloration and thermal maturation The color of fresh spore exines in transmitted light ranges from pale yellow to almost colorless and they changed by time and temperature (e.g., by deep burial or proximity to a lava flow), from yellow, orange to brown, dark brown and finally black [23]. In the present work, simple thin-walled psilate palynomorphs (e.g., Cyathidites australis) were chosen to investigate their exines color using Pearson’s [24] color chart and [25] scale of palynomorph colors to estimate approximately the numerical thermal alteration index (TAI), vitrinite reflectance (Ro%) and organic thermal maturity in the studied wells. The change in color of the recovered spores in the successions of both wells is as follows: 1. The samples from the Kharita Formation contain abundant brown phytoclasts. The color of the Cyathidites australis spore grains are immature dark yellow to orange, which indicating a thermal alteration index (TAI) ranges between 2 and 2 and vitrinite reflectance of 0.5% [24]. 2. The samples from the Bahariya Formation display translucent and brown phytoclasts. The color of the Cyathidites australis spore grains did not change from the older samples from Kharita Formation. The color ranged between immature dark yellow and orange, which indicates a thermal alteration index between 2 and 2 and vitrinite reflectance of 0.5% [24].
4.3. Hydrocarbon generation potentiality depending on the palynofacies analysis and spore coloration Depending on the palynofacies analysis, the hydrocarbon generation potentiality is poor in both of these formations (kerogen types range between gas prone III and oil prone II) and they are immature to yield any hydrocarbons. The previous studies in the Western Desert confirm the present conclusion, where the samples from Bahariya and Kharita formations were immature and of poor hydrocarbon generation potentiality [2,5,8–10]. The integrating of the results between these works perhaps means that the conditions during the deposition of both studied formations were uniform through at least the northern part of the Western Desert. This study suggests the increasing of the marine influence in the north, where more AOM accumulations are expected although it depends on other paleoenvironmental conditions (like oxygen content). The higher potentiality to be source rocks or to generate hydrocarbons in Bahariya and Kharita formations should be in the deeper offshore region to the north of the location of the present studied area. 4.4. Organic geochemical analysis It is based on the integration between the palynofacies assessment of the kerogen type and organic geochemical analysis by using the Rock-Eval-6 pyrolysis analyzer. This integration allows simultaneous visual and quantitative control on the hydrocarbon generation potentiality. [26–28]. 4.4.1. Organic richness and hydrocarbon potentiality The organic richness of any source rock is determined by the total organic carbon ‘‘TOC” in the whole rock and pyrolysis derived ‘‘S2”of the rock samples [28]. Eighteen representative ditch samples from El Noor Well were analyzed by Rock Eval-6 to obtain the geochemical pyrolysis data represented in (Table 3).
Please cite this article in press as: N.A. Ela et al., Source rock evaluation of Kharita and Bahariya formations in some wells, North Western Desert, Egypt: Visual palynofacies and organic geochemical approaches, Egypt. J. Petrol. (2017), http://dx.doi.org/10.1016/j.ejpe.2017.07.009
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Fig. 9. Rock Eval pyrolysis data of El Noor well. (a) TOC (b) S2 (C) Tmax.
In the study samples of Kharita Formation the TOC values range from 0.50 to 1.21 wt% (Table 3), which represents Fair to good organic richness (Fig. 9). The S2 values ranges from 0.09 to 0.69 mg./g. which represent poor generating source, (Fig. 9b). In the Bahariya Formation, the total organic carbon content ‘‘TOC” values ranging from 0.43 wt% to 3.19 wt% which represent fair to good total organic carbon content with one sample lies in the very good zone (Fig. 9a). The generating source potential ‘‘S2” ranges from 0.17 to 2.24 mg/g (Table 3), indicating poor S2 content (Fig. 9b).
4.4.2. Genetic type of organic matter The type of organic matter completes the organic richness in evaluating the generating potential of a source rock. Its origin may be terrestrial, as in case of peats, lignites and coal seams or aquatic, as in case of animal and fungal remains, or mixture of both, as in case of many oil shales and presumed oil-source rocks [20]. In the present study we use the pyrolysis method, the hydrogen index ‘‘HI” values of the Kharita Formation in El Noor well ranges from 19 to 63 (mg./g.) and the ‘‘OI’ values ranges from 16 to 110 (mg./g.) respectively, while Bahariya Formation in El Noor well
Please cite this article in press as: N.A. Ela et al., Source rock evaluation of Kharita and Bahariya formations in some wells, North Western Desert, Egypt: Visual palynofacies and organic geochemical approaches, Egypt. J. Petrol. (2017), http://dx.doi.org/10.1016/j.ejpe.2017.07.009
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inated with terrestrial phytoclastic materials in both studied formations (Figs. 2–8) [30]. 4.5. Organic thermal maturation In the present study various parameters used to estimate source rock maturation. as vitrinite reflectance (Ro), the temperature at which the kerogen yields maximum hydrocarbons (Tmax.) [31]. Espitalie et al. [32] and Peters [33] reported that oil generation from source rocks began at ‘‘Tmax.” 435–465 °C, vitrinite reflectance ‘‘Ro%” between 0.5% and 1.35% and production index ‘‘Pl” between 0.1 and 0.4. ‘‘Tmax.” has a value less than 435 °C, ‘‘Ro”% less than 0.5% and ‘‘Pl” less than 0.1; represents organic matters in the immature stage. Gas generation from source rocks began at ‘‘Tmax.” 470 °C, vitrinite reflectance is more than 1.35% and production index ‘‘Pl” more than 0.4. In the study samples the Tmax.values for the Kharita Formation ranges from 429 to 435 °C (Table 3) which represents immature to marginally mature samples to yield hydrocarbons (Fig. 9c), the Tmax. values for Bahariya Formation ranges from 432 to 438 °C (Table 3) which represent immature to marginally mature rock (Fig. 9c), and the expected hydrocarbon to be generated from the samples in case of maturation can be obtained by plotting the TOC vs. HI [26].The study samples in case of maturation are capable of generating mainly gas hydrocarbon (Fig. 11) [34] Fig. 10. Modified Van Krevelen type diagram showing kerogen type of the studied. samples of El Noor well (after Waples [28]).
5. Conclusions The present palynofacies analysis carried on the subsurface Albian – Cenomanian Kharita and Bahariya formations, encountered in El-Noor and South Sallum wells are illustrating potential results concerning with their depositional paleoenvironments and source rock probability in the northern Western Desert. Five palynofacies associations were recognized. Kharita Formation took place mainly in a steady and a relatively stable deltaic to marginal environment. The marine influence became more common in the upper part of Bahariya Formation showing the exceptional high hydrocarbon potential. Such rising in the marine influence indicates marine transgression by the end of the early Cenomanian time. Kharita Formation indicates possibility to gas-prone kerogen type III and IV, while most of Bahariya Formation points to more promising gas-prone kerogen type III. This study demonstrates poor to fair gas-prone source rock potential within the Albian Cenomanian section. Thermally, the color of the spore grains Cyathidites australis in Kharita and Bahariya formations illustrates immature dark yellow to orange, according to Thermal Maturation Index (TAI). Acknowledgment
Fig. 11. Source Rock characterization using plot of HI vs. TOC. (Jackson et al., 1985) [34].
range from 27 to 155 (mg./g.) and oxygen index ‘‘Ol” from 7 to 107 (mg./g.), (Table 3). These data reflect that the main expected kerogen type is type (III) for producing (gas) as shown in the modified Van Krevelen diagram (Fig. 10). This conclusion reflects that the main organic source material is terrestrial organic matter [29]. It is well integrated and supported with the palynofacies examinations, which revealed almost the same kerogen types that are dom-
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Please cite this article in press as: N.A. Ela et al., Source rock evaluation of Kharita and Bahariya formations in some wells, North Western Desert, Egypt: Visual palynofacies and organic geochemical approaches, Egypt. J. Petrol. (2017), http://dx.doi.org/10.1016/j.ejpe.2017.07.009