Journal of African Earth Sciences 104 (2015) 19–26
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Journal of African Earth Sciences
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Source-rock evaluation of the Dakhla Formation black shale in Gebel Duwi, Quseir area, Egypt
M.M. El Kammar
Department of Geology, Faculty of Science, Cairo University, Egypt article info abstract
Article history: A relatively thick Upper Cretaceous–Lower Tertiary sedimentary succession is exposed in Gebel Duwi, Received 30 June 2014 Red Sea area, through an almost horizontal tunnel cutting the NE dipping strata from Quseir to Thebes Received in revised form 11 January 2015 formations. The black shale belonging to Dakhla Formation represents a real potential for future energy Accepted 12 January 2015 resource for Egypt. Dakhla Formation consists mainly of organic-rich calcareous shale to argillaceous Available online 28 January 2015 limestone that can be considered as a good to excellent source rock potential. The total organic carbon (TOC) content ranges from 2.04% to 12.08%, and the Hydrogen Index (HI) values range from 382 to Keywords: 1024 mg HC/g TOC. Samples of the Dakhla Formation contain mostly kerogen of types I and II that prone Black shale oil and oil-gas, indicating marine organic matter derived mainly from algae and phytoplankton organisms Source rock Duwi and proposing typical oil source kerogen. The average of the potential index (PI) value is 0.02 mg HC/g Dakhla Formation rock, which indicates the beginning of a considerable amount of oil generation from the Dakhla Kerogen Formation. The Tmax values range from 427 to 435 °C. Based on the Tmax data and PI values, the studied Calorific value black shale samples are immature to early mature for hydrocarbon generation in the Duwi area. The data reduction suggests four main factors covering about 91% of the total variances. The average of the calorific value (459 kcal/kg) indicates unworkable efficiency of such black shale for direct combustion use in power stations. However, selective operation of specific horizons having the highest calorific values may provide viable resources. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction of this ridge ranges between 450 and 545 m above sea level. The stratigraphic succession includes the formations from Nubia The increased interest in black shale, all over the world during Formation, as the oldest sedimentary unit in the region the last few decades, seems principally to be due to their impor- (Cenomanian, Upper Cretaceous) to Nakheil Formation (Oligocene) tance as natural unconventional future fuel-resources. The black with a dip of ±20°NE. shale is widely distributed in Egypt in several horizons of different Many studies have focused on the oil potential of the black geologic ages, particularly in the Upper Cretaceous–Lower Tertiary shale of the region. The first of these studies was performed by formations; Duwi (phosphate-bearing), Dakhla and Esna forma- Mustafa and Ghaly (1964), followed by several others such as tions in the area between Safaga and Quseir of the Red Sea region. Tröger (1984), Ganz (1984), Khaled et al. (1987) and El-Kammar The black shale belonging to the Dakhla Formation represents the (1987, 1993, 2014). However, most of these studies focused on real potential resources of Egypt. The average amount of oil yielded the geochemistry, depositional environment, stage of maturity by Fischer assay is about 20–45 gal/ton (Robison and Tröger, 1983; and potential for hydrocarbon generation of the black shale of Tröger, 1984). The in-place shale-oil resources in Quseir–Safaga the Dakhla Formation. In addition, the organic geochemical charac- area is 4500 ⁄ 106 bbls (Tröger, 1984). These estimations are not teristics using biomarker parameters were studied by El-Kammar beyond doubt because they were calculated on the basis of mea- (1993) in order to characterize the organic matter and its matura- surement of surface exposures and spot samples collected from tion. More advances have recently been projected by El-Shafeiy abandoned phosphorite mines (El-Kammar, 2014). The geological et al. (2014). formations of the Upper Cretaceous–Lower Tertiary are well exposed in Gebel Duwi to the west of Quseir. It covers an area of 2. Regional geology about 112 km2 (28 km long and 4 km wide, Fig. 1). The elevation Geologically, Gebel Duwi area is a part of the Central Eastern E-mail address: [email protected] Desert of Egypt that can be subdivided into two parts; the Duwi http://dx.doi.org/10.1016/j.jafrearsci.2015.01.001 1464-343X/Ó 2015 Elsevier Ltd. All rights reserved. 20 M.M. El Kammar / Journal of African Earth Sciences 104 (2015) 19–26 range and the coastal plain. The former consists of an elongate sediments that were deposited in two main conformable geological NW-trending ridge that drops precipitously to the southwest and formations, namely; Duwi and Dakhla formations. The former is slopes gently to the northeast. The coastal plain is generally mostly Campanian to early Maastrichtian in age and it includes smooth in outline, with no sharp bends or bays. It slopes gently the economic phosphate deposits of Egypt. The Dakhla Formation seaward. In general, the sedimentary rocks of Gebel Duwi area was deposited in near shore to deep marine environments during are separable into two main divisions: the pre-rift Cretaceous– Maastrichtian to Early Paleocene as indicated by the presence of Eocene succession (more than 1500 m thick) and the syn-rift Oligo- dinoflagellates, nannoplanktons, planktonic foraminifera and paly- cene and younger sediments (Fig. 1). The Cretaceous and Eocene nology (Abdel-Malik, 1982; Schrank, 1984, 1987; El-Kammar et al., deposits occupy the troughs of synformal-like fault-folds within 2013). the crystalline hill ranges. In the Quseir–Safaga district, the Dakhla Formation reaches its The stratigraphy of Gebel Duwi area is summarized below, pri- maximum thickness in Gebel Duwi (175 m) and can be subdivided marily after Said (1962). The typical stratigraphic section in the into two members; lower Hamama (Marl) Member (Maastrichtian) Quseir–Safaga region starts at its base with the non-fossiliferous, and upper Beida (Shale) Member (Paleocene). The latter is com- cross-bedded Nubia (sandstone) Formation which represents the posed of gray shale and unconformably overlies the Hamama oldest sediments in the area which unconformably overlie the Member (Masters, 1984). El-Kammar (1987) reported a remarkable basement rocks. The Nubia Formation is conformably overlain by feature in the Quseir and Safaga phosphate mines where the cap- thick multicolored shale known as Quseir (Variegated Shale) For- ping black shale caught fire by self-ignition being rich in hydrocar- mation. Both Nubia and Quseir formations have a pre-Campanian bons and pyrite. age. The Quseir Formation constitutes the base of black shale-bear- ing formations and is overlain by Duwi and Dakhla formations (Fig. 1). The black shale of both Duwi and Dakhla formations are 3. Materials and methods assigned Upper Campanian to Maastrichtian age which provides a good example of major marine transgression event. The sedimen- The Dakhla Formation, consisting of thick black shale strata, tary association of that event consists of black (frequently assigned was systematically sampled from a tunnel that was excavated in as ‘‘oil’’) shale, limestone, phosphorite, chert, glauconite and the early 1930s almost horizontally to cut the NE dipping sedimen- dolostone. tary strata starting from Quseir Formation (old) to Thebes Forma- Major marine transgression during the Late Cretaceous–Early tion (young). The tunnel starts at the south-western flank of the Tertiary times covered most of the Egyptian territory southwards Duwi range, near to Beida mine (at longitude 34°0500200E and lati- up to latitude of Aswan (24°N). It was interrupted by minor mild tude 26°0900000N) and terminates in Wadi El-Nakeil (at longitude regressive, and some tectonic, pulses associated with uplifting 34°0505800E and latitude 26°0603900N). It was dug by an Italian phos- (Issawi, 1968; Said, 1990; El-Sabbagh et al., 2011). The marine phate company to provide systematic profiling and sampling of the depositional conditions during the transgression maintained favor- Upper Cretaceous–Lower Tertiary sedimentary sequence, in gen- able conditions for accumulation and preservation of organic-rich eral, and phosphorites in particular (Fig. 1). The tunnel runs almost
Fig. 1. Geologic map of the Gebel Duwi showing the different stratigraphical units of the study area (modified after Khalil and McClay (2002)). M.M. El Kammar / Journal of African Earth Sciences 104 (2015) 19–26 21 horizontal to traverse the NE dipping sedimentary strata. The foot an average of 4.35% (Table 1). The aforementioned data suggest of the tunnel at its south-western side is made of the uppermost that the sediments of the Dakhla Formation are markedly rich in Quseir (variegated shale) Formation whereas its north-eastern ter- organic content and can be considered as good to excellent source. minal at Wadi El-Nakheil is mostly of Thebes (limestone) Forma- Typical oil-prone, marine source rocks contain 2–5% TOC, but tion. The tunnel, as such, traverses the complete section of the strata in the range of 10–20% are known to occur in high yield Duwi, Dakhla, Tarawan and Esna formations. A total of 110 sam- petroleum systems (Peters et al., 2005). The highest TOC content ples were collected to represent the variation in the almost non- determined for the study samples is 12.08%, but much higher val- weathered facies of the Dakhla Formation. The TOC was analyzed ues of 22% and 24%, were obtained for spot samples by Mustafa and in a total of about 85 samples, where samples containing less than Ghaly (1964) and El-Kammar (1993), respectively. 2% TOC have been exempted, being classified as organic-poor sed- In spite of the fact that the TOC is an important criterion for the iments. Sixty four samples containing more than 2% TOC from the source rock evaluation, other parameters such as the kerogen type, Dakhla Formation were selected for geochemical assessment by sulfur content and lithology are even more imperative. The distri- Rock-Eval pyrolysis and calorific value as well as sulfur content. bution of the sulfur content seems to be independent on the Detailed descriptions of the Rock-Eval pyrolysis technique and organic carbon richness (Fig. 2). Recognition of sulfur in the form the interpretation of source rock parameters were performed fol- of framboidal pyrite suggests microbial activity under euxinic con- lowing standardized procedures in Espitalié (1986), Peters (1986) ditions. The sulfur content ranges from 0.04% to 2.64% with an and Peters and Cassa (1994). The measured parameters include average of 1.18%. Free Oil Content (S1 mg HC/g rock), Source Potential (S2 mg HC/g rock), and thermal maturity (Tmax °C). Source rock parameters such 4.2. Kerogen type as Hydrogen Index (HI), Oxygen Index (OI), Production Index (PI) and Pyrolyzable Carbon Index (PCI) were calculated. The Produc- Based on the results of the pyrolysis analysis, the S1 values are tion Index (Transformation Ratio) is the proportion of free hydro- in the range of 0.13–2.40 with an average of 0.52 mg HC/g rock carbons in relation to the total amount of hydrocarbon (Table 1). On the other hand, the S2 values, which represent the compounds obtained by the sample analysis (Othman, 2003). The fraction of the organic matter that can be transformed into hydro- PI is also used to assess the relative thermal maturity of organic carbons during catagenesis via high temperature and pressure, matter (Peters, 1986; Tissot and Welte, 1984). In general, PI values range from 10.0 to 112.7 mg HC/g rock, suggesting good to excel- below 0.4 indicate immature organic matter; PI values between 0.4 lent source rock character, where most of the samples have S2 and 1.0 indicate mature organic matter; and PI values above 1.0 are more than 10 mg HC/g rock. The plot of the obtained data on the indicative of over mature organic matter. TOC versus S2 diagram illustrates that kerogen belongs mostly to The Pyrolyzable Carbon Index is a maximum amount of hydro- type I and/or type II (Fig. 3). In agreement with Dahl et al. carbon that a sample is able to generate during the analysis, and (2004), the depositional environments were lacustrine and marine mathematically can be expressed as PCI = 0.83 (S1 + S2) (Reed where organic matter is mostly derived from marine algae and and Ewan, 1986; Pimmel and Claypool, 2001; Shaaban et al., phytoplankton organisms, suggesting a typical ‘‘oil source’’ 2006). The PCI can be used to estimate the kerogen type and its kerogen. hydrocarbon potential (Reed and Ewan, 1986; Shaaban et al., The distribution of the hydrogen index confirms the conclusion 2006). The PCI values: P75 indicates type I; 40–50 represents type that Dakhla Formation incubates the highest proportion of kerogen II; and <15 indicates type III (Reed and Ewan, 1986). The samples types I and/or II, reflecting higher contribution of marine organic were analyzed in the organic geochemistry laboratories of the matter. However, for more precise designation of the kerogen qual- Strato Chem ServicesÓ in Cairo, Egypt. The analysis of calorific val- ity, the plot of the Hydrogen Index (HI in mg HC/g TOC) versus the ues and sulfur content were done by Oxygen Combustion Bomb Oxygen Index (OI in mg CO2/g TOC) has been constructed (Fig. 4). and Leco-analyzer techniques, respectively, in the Central Labora- The HI values are in the range of 382–1024 with an average of tories of the Ministry of Electricity of Egypt. 678 mg HC/g TOC. The best quality of organic matter that possesses HI 1024 mg HC/g TOC has been encountered in the lowermost part of the Dakhla Formation. The number of cases belonging to kero- 4. Results and discussions gen quality of type I, that possesses HI > 600 mg HC/g TOC, are about 50 samples out of total 64 samples. This distribution signi- The present work is based on original Rock-Eval analysis data fies that the quality of kerogen is essentially controlled by the and calorific measurements of 64 samples, representing the com- transgression of the depositional sea and, consequently, higher plete section of the Dakhla Formation in Gebel Duwi in the Quseir contribution of the autochthonous, relative to the allochthonous, area. organic matters. The Genetic Potential (S1 + S2) of a given formation is defined as 4.1. Organic richness the amount of petroleum (oil and gas) that kerogen is able to gen- erate, if it is subjected to an adequate temperature during a suffi- In the following context, samples containing less than 2% TOC cient interval of time (Tissot and Welte, 1984). This potential have been marginalized, since the main concern is the evaluation depends on the nature and abundance of kerogen, which is, in turn, of the organic-rich sediments. Therefore, the data rank (n = 64) related to the original organic input at the time of deposition, and represents the sediments containing >2% TOC of the Dakhla Forma- to the conditions of microbial degradation, and the re-arrangement tion where thickness, lithology, organic-richness, kerogen type and of organic matter in the sediments. The Genetic Potential gives a limits of maturation vary significantly from one horizon to the qualitative estimate of hydrocarbon resource potential; however, other. The highest TOC content (12.08%) of the transgressive Dak- it cannot be used to predict the type of hydrocarbons (gaseous or hla Formation depends on the rate of the primary bio-productivity, liquid) that will be produced during pyrolysis. The potentiality of the terrestrial contribution, the preservation and dilution of the study succession has been proposed on basis of the relationship organic matter. This agrees with conclusions reported by Glenn between the TOC content and the Genetic Potential values and Arthur (1985), Betts and Holland (1991), Tyson (1987, 2001, obtained for the analyzed samples. The organic matters within 2005), Katz (2005) and El-Kammar (2014). The TOC values of the the study samples have high potentiality for hydrocarbon study black shale samples range between 2.04% and 12.08%, with generation, ranging mostly between good and excellent (Fig. 5). 22 M.M. El Kammar / Journal of African Earth Sciences 104 (2015) 19–26
Table 1 Descriptive statistics of the resulted data for Lower and Upper Dakhla Formation.
Geological formation Lower Dakhla Formation Upper Dakhla Formation Variables Min. Max. Mean (n = 34) Std. deviation Min. Max. Mean (n = 30) Std. deviation TOC % 2.33 12.08 4.52 1.67 2.04 10.69 4.16 1.55 S1 mg HC/g rock 0.13 2.40 0.46 0.41 0.17 2.39 0.59 0.58 S2 mg HC/g rock 11.57 112.74 33.51 17.64 10.01 60.54 28.09 12.75 S3 mg HC/g rock 0.89 1.59 1.25 0.18 0.52 3.86 1.28 0.73
Tmax °C 422 435 428 3 413 434 427 5 HI mg HC/g TOC 456 1024 712 114 382 959 640 143
OI mg CO2/g TOC 7.43 52.93 30.61 9.49 18.56 69.21 30.50 12.98 S1/TOC 5.60 29.11 9.35 4.65 4.50 35.07 12.25 8.00 PI 0.01 0.03 0.01 0.00 0.01 0.04 0.02 0.01 GP 11.70 115.14 33.97 18.02 10.20 62.93 28.68 13.26 PCI 9.70 95.60 28.23 14.94 8.50 52.20 23.81 11.00 Sulfur % 0.07 2.64 1.36 0.62 0.04 1.75 0.97 0.39 Calorific value kcal/kg 210 1139 502 180 231 858 408 130 HI/OI 9.37 126.65 27.63 19.52 6.35 43.69 24.30 10.33
Fig. 2. Sulfur content versus TOC contents of the black shale samples of Dakhla Formation.
Fig. 4. HI versus OI cross plot of Dakhla Formation in Gebel Duwi Tunnel (Espitalié, 1986).
easily concluded that the organic matter in the black shale of the Fig. 3. The hydrocarbon potentiality of Dakhla Formations as shown by using TOC % Dakhla Formation is mostly of marine origin and is capable to gen- versus S2. erate mostly oil and rarely gas.
4.3. Thermal maturity Considering that the main lithology of the Dakhla Formation is argillaceous limestone, it can be assigned as good to excellent Level of thermal maturity for the different types of organic source rock. However, the highest TOC content (12.08%) is matter may be estimated from the Tmax range and Production Index recorded in the lower part of the Dakhla Formation. Similar trend (Peters and Cassa, 1994; Bacon et al., 2000). The measured Tmax val- can be supposed for the pyrolyzable organic content (GP) as ues confirm the immature nature of the organic matter, just close expressed by S2 values as well as the bituminous content (S1), to the early oil maturation window. The plot of the hydrogen index where S1 measures 2.4 mg HC/g rock. versus Tmax (Fig. 6) suggests that the definition of kerogen type is The kerogen type classification diagrams; namely S2 versus TOC only restrained on basis of HI, since the variation in Tmax is very (Fig. 3) and HI versus Tmax (Fig. 6), confirm the aforementioned limited (generally between 413 and 435 °C). The vitrinite reflec- recorded kerogen types, where most of the analyzed samples tance (Ro) can be estimated from the Tmax values obtained from belong to type I and I/II kerogen field whereas few samples plot the Rock-Eval pyrolysis (Dembicki Jr., 2009). The conversion can in the type III kerogen field. Based on the above data, it can be be mathematically expressed as: Rcalculated = (0.018 ⁄ Tmax) 7.16. M.M. El Kammar / Journal of African Earth Sciences 104 (2015) 19–26 23
100 ppm, concluded that the heat produced from uranium decay cannot explain the heterogeneous spatial distribution of the matu- ration levels that may reach 10%. He added that the straightfor- ward explanation of the sporadic high maturation in the high grade oil shale of Quseir area can only be attributed to temperature and pressure triggered by tectonics related to rifting of the Red Sea and dragging of sedimentary sequence during the uplift of crystal- line rocks. The present author believes, however, that maturation is related directly or indirectly to the kerogen type. The liptinitic ker- ogen is liable to produce bitumen much faster than other kerogen classes. This assumption is supported by the positive correlation between the HI/OI ratio, as a straight measure for kerogen type, and S1/S2, as a maturity indicator (Fig. 7). The maturity levels for the oil window depend on the type of organic matter (Bacon et al., 2000). Fig. 5. The hydrocarbon potentiality of Dakhla Formation by using TOC % versus GP (S1 + S2). 4.4. Calorific value
This formula is applicable for type II and type III kerogen as sta- The calorific value is determined for 64 samples to assess the ted by Peters et al. (2005). The obtained calculated R data are rea- o efficiency of the study black shale as energy donor. The calorific sonable, when the analyzed samples have S2 values more than
0.5 mg HC/g rock and samples with Tmax <420 °C or >500 °C (Peters et al., 2005). The calculated vitrinite reflectance (Rcalculated) values of the Dakhla Formation samples indicate immaturity to early maturity, where all samples show Rcalculated values less than 0.67 (Fig. 6). The maturated fraction of the organic matter, even at the 2% level, cannot be explained in terms of burial catagenesis, because the depth of the study Dakhla Formation is about 100 m. Khaled (1991) attributed maturation in Quseir area to heat produced by decay of uranium in phosphorite underlying these prolific hori- zons. Mapping of radioactive heat production from airborne spec- tral gamma-ray of Gebel Duwi was constructed by Salem et al. (2005). They concluded that the sedimentary rocks in Gebel Duwi area have higher heat production value (0.25–3.09 lWm 3) than the crustal average for sedimentary rocks. El-Kammar (2014), based on the fact that the average uranium content in the sedimen- tary succession of Duwi and Dakhla formations in Quseir area is only 9.4 ppm and its maximum concentration in phosphorite is Fig. 7. Plot of HI/OI versus S1/S2 of Dakhla Formation in Gebel Duwi Tunnel.
Fig. 6. Tmax and vitrinite reflectance versus the Hydrogen Index (HI) cross plot after Espitalié (1986) gives an overview of the thermal maturity and variation of organic matter quality for Dakhla Formation. Tmax values correlate directly with vitrinite reflectance values. 24 M.M. El Kammar / Journal of African Earth Sciences 104 (2015) 19–26 value of the analyzed samples defines the suitability of the organic Table 2 rich samples for direct combustion utilization, such as power sta- Summary of the resulted data reduction of the Dakhla Formation in Quseir area (Number of samples = 64). tions. The obtained values range from 210 to 1139 kcal/kg with an average of 459 kcal/kg. The Russian UTT-3000 and the Finish Factor 1 Factor 2 Factor 3 Factor 4 EnfitÓ technology, among other technologies, can operate black Eigenvalue value 7.82 2.12 1.68 1.09 Variance % 55.84 15.14 12.03 7.81 shale quality of 900 kcal/kg. Factors’ name Maturation Dead carbon Calorific value Sulfur Therefore, the average quality of the black shale belonging to TOC 0.89 0.02 0.33 0.08 the Dakhla Formation in Quseir area is much beyond the workable S1 0.9 0.33 0.14 0.16 limits. However, selective mining operation of the prolific horizons S2 0.97 0.12 0.11 0.14 can satisfy part of the increasing energy gap in Egypt. It is impor- S3 0.16 0.75 0.53 0.31 tant to notice that the calorific value is a function of TOC content Tmax 0.76 0.27 0.28 0.19 as well as the Pyrolyzable Carbon Index (Fig. 8). HI 0.72 0.24 0.2 0.36 OI 0.51 0.65 0.33 0.24 S1/TOC 0.7 0.44 0.47 0.23 PI 0.47 0.67 0.4 0.36 4.5. Statistics and data evaluation GP 0.97 0.11 0.11 0.13 PCI 0.97 0.11 0.11 0.13 The data reduction suggests four main factors covering about Sulfur 0.28 0.1 0.55 0.7 91% of the total variances. The first and the most influential factor Calorific value 0.72 0.02 0.56 0.15 HI/OI 0.83 0.45 0.11 0.02 covers about 56% of the variances and expresses the influence of the organic richness as the factor loads positively for TOC, S1, S2 Italic = Positively Loaded. Bold = Negatively Loaded. and hydrogen index (Table 2). The second factor expresses 15% of the total variances rational- izing the effect of the degraded carbon (S3) and the Oxygen Index (OI). The third and fourth factors represent the influence of calorific of 2400 kcal/kg, for the black shale at the lowermost Dakhla For- value and sulfur content, respectively. Accordingly, it can be stated mation in Nakhiel mines area. However, the intervals that contain that the heat yield, as measured by calorific value, is not straight- workable pyrolyzable kerogen or heat content feasible for direct forward dependent on TOC or S2. The present author believes that combustion or retorting on a commercial scale are limited and the calorific value is possibly a function of multi-variables includ- can only be exploited through selective subsurface mining opera- ing kerogen type in addition to TOC, sulfur content and humidity. tions. The low sulfur content of the study black shale can be con- In spite of the fact that Dakhla Formation in the Quseir area is sidered as positive technical property. The high content of sulfur diagnostically enriched in organic matter, the kerogen of the lower may enhance the harmful atmospheric emission of hydrogen sul- part seems relatively to be of superior class. The lower and upper fide during combustion or retorting. parts of the Dakhla Formation have almost similar TOC content; The S1 content expresses the maturated proportion of the 4.52% and 4.16%, respectively, but the important differences are organic matter and the S1/S2 ratio can be considered as a measure those recorded in the pyrolyzable kerogen (S2) as well as Hydrogen of the maturation level. In the present work, the S1 content varies Index (HI) and calorific value (Table 2). The high S2 (up to 112.7 mg between 0.13 and 2.4 mg HC/g rock, whereas the S2 content ranges HC/g rock) and HI (up to 1023.6 mg HC/g TOC) are clear symptoms between 10.01 and 112.74 mg HC/g rock (Fig. 8), suggesting insig- of the better class of kerogen. This, in turn, explains the higher heat nificant level of maturation. However, considering the fact that the yield of the calorific value for the lower Dakhla Formation which sampled tunnel was excavated at the early 20th century, the mat- reaches 1139 and averaging 501 kcal/kg, whereas the highest value urated volatile bituminous materials must have escaped. The pres- for the upper part is 857 and averaging 408 kcal/kg. The lowermost ent S1 content represents less than 2% of the total organic content, horizon of the Dakhla Formation, adjacent to contact with the while the data of core samples in Quseir area contain more than Duwi Formation is apparently the most prolific horizon. This 10%, as reported by El-Kammar (2014). The measured S1 in the agrees with data given by Tröger (1984), El-Kammar et al. (1990) present work may represent the residual bitumen after surface and El-Kammar (1993). The last author quoted much higher value degradation for about a century (see Fig. 9).
Fig. 8. The positive interrelationship of calorific value versus TOC and Pyrolyzable Carbon Index of the Dakhla Formation in Gebel Duwi Tunnel. M.M. El Kammar / Journal of African Earth Sciences 104 (2015) 19–26 25
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