Dec 8, 2016 - Petroleum Science and Technology ... Petroleum Research Institute, Nasr City, Cairo, Egypt ..... in the vicinity of Siwa Oasis, Western Desert.
Petroleum Science and Technology
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Isopach, lithofacies changes, and source rocks chracteristics of Khatatba and Alam El Bueib formations of some wells in North East Western Desert, Egypt Fatma S. Ramadan, Mohmed M. El Nady, Emad A. Eysa & Samr A. Mahdy To cite this article: Fatma S. Ramadan, Mohmed M. El Nady, Emad A. Eysa & Samr A. Mahdy (2016) Isopach, lithofacies changes, and source rocks chracteristics of Khatatba and Alam El Bueib formations of some wells in North East Western Desert, Egypt, Petroleum Science and Technology, 34:23, 1920-1928 To link to this article: http://dx.doi.org/10.1080/10916466.2016.1238931
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Date: 08 December 2016, At: 21:11
PETROLEUM SCIENCE AND TECHNOLOGY , VOL. , NO. , – http://dx.doi.org/./..
Isopach, lithofacies changes, and source rocks chracteristics of Khatatba and Alam El Bueib formations of some wells in North East Western Desert, Egypt Fatma S. Ramadana , Mohmed M. El Nadyb , Emad A. Eysaa , and Samr A. Mahdya a Geology Department, Faculty of Science, Zagazig University, Zagazic City, Egypt; b Exploration Department, Egyptian Petroleum Research Institute, Nasr City, Cairo, Egypt
ABSTRACT
KEYWORDS
The present work deals with isopach, lithofacies changes, and source rock chracteristics of Khatatba and Alam El Bueib formations of some wells in North East Western Desert. Isopach and lithofacies changes showed that the thickness of Khatatba Formation increases toward the south western direction and decreases toward northern parts, and the sediments consisting of sandstone and shale facies indicate a shallow marine environment. Alam El-Bueib sediments increase toward the north direction, and argillaceous sandstone facies reflect terrestrial-to-shallow marine environment. The geochemical analysis showed that Khatatba Formation bears a mature source rock and has poor-togood generating capability for both oil and gas and lie within the early generation window and oil window. Alam El Buieb Formation constitutes a mature source rock and has poor-to-good generating capability for both oil and gas. It can be stated that Khatatba and Alam El Buieb are the main source rock for hydrocarbon accumulations rich with organic sediments and could be considered as effective source rocks for generating hydrocarbons in the the studied wells.
Egypt; isopach; lithofacies; source rock; Western Desert
1. Introduction The Western Desert of Egypt represents an important part of the unstable shelf of the Northern Africa and comprises a total area of 700,000 km2 , west of the Nile River and Delta. It extends from the Libyan borders in the west of the Nile Delta and Nile River in the east, and from the Mediterranean Sea Coast to the Sudan borders in the south. The Western Desert has numerous oil potentialities and may soon jump as a great oil province. The study area is located in the northern part of the Western Desert at north Abu ghradig basin between latitudes 30°03 and 33°00 N and longitudes 28°9 and 28°14 E (Figure 1). The general structural and stratigraphical aspects of the Western Desert have been the subject of many studies, such as Meshref (1982), El-Khadragy and Sharaf (1994), Shalaby et al. (2000), and El-Khadragy et al. (2010). Geochemical characteristics of source rocks in the Western Desert have been discussed by many authors such as Abdel Aziz (1994), El Nady and Sharfe (2004), El Nady (2013, 2015, 2016a, b), El Nady and Mohamed (2016), El Nady and Hakim (2016), Rammadan et al. (2014), and El Nady et al. (2015, 2016). The main objectives of this study are: (i) trace the thickness variations and triangle facies change of the penetrated formations and assess the depositional environments of the different rock units, (ii) identify
CONTACT Mohmed M. El Nady mohamedelnady@gmail.com Exploration Department, Egyptian Petroleum Research Institute, -Ahmad El-Zomor St., , Nasr City, Cairo, Egypt. Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lpet. © Taylor & Francis Group, LLC
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Figure . Base map showing the studied wells in the North East Western Desert, Egypt.
and characterize potential source rocks and their generating capability, (iii) investigate the maturation level of the proven potential source formations for oil preservation, and (iv) predict the levels of thermal maturity of the studied formations in terms of hydrocarbon generation.
2. Materials and methods Four representative composite logs wells are JG-1, JG-2, JG-8, and JG-9. Eighty-eight cutting samples of argillaceous sandstone and shales, representing Jurassic rock units (Khatatba Formation) and Lower Cretaceous rock units (Alam El Bueib Formation), were collected from JG-1 well at different depths. The composite logs and geochemical data of samples were supplied by Egyptian General Petroleum Corporation approval (EGPC). 1. Isopach and lithofacies maps of the studied rock units were constructed to show the thickness and facies variation of different rock units. 2. Rock-Eval/total organic carbon (TOC) analysis was carried out by a Rock-Eval II analyzer procedure was used by Espitalie et al. (1985) to obtain TOC wt%, free hydrocarbons (S1 = mg HC/g rock), and residual petroleum potential (S2 = mg HC/g rock). All these parameters are used in the present work to determine the hydrogen index (HI = mg HC/g TOC) and oxygen index
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Figure . Isopach (a) and triangle facies (b) maps of Khatatba Formation, North East Western Desert, Egypt.
(OI = mg CO2 /g TOC), generating potential (GP = S1 + S2), and type of hydrocarbons products (QI = S2/S3).
3. Results and discussion 3.1. Isopach and lithofacies changes The isopach map of the Khatatba Formation (Figure 2a) shows an increase in its thickness toward southwest direction reaching a maximum thickness of 508 m near JG-9 well and decrease at northern parts reaching a minmuim thickness of 448 near JG-1well. These variations in thickness may be due to the uplifting followed by erosion of this formation. Moreover, this map reflects one main depocenter located around the JG-9 well. Furthermore, the wide contour lines shown in the northern and northeastern parts of the study area may indicate a gentle subsidence of deposition than the other parts or may indicate that the area was still high during the transgression of the sea (onlap). Triangle facies map of Khatatba
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Figure . Isopach (a) and triangle facies (b) maps of Alam El Buieb Formation, North East Western Desert, Egypt.
Formation shows that the sediments consist of sandstone and shale facies. Sandstone facies are represented by argillaceous sandstone around JG-2A and JG-8 wells. Shale facies are represented by calcareous shale around JG-1 and JG-8-ST wells. These facies indicate a shallow marine depositional environment (Figure 2b). Alam El-Bueib Formation consists of sandstones interbedded with shales and isopach map of Alam El-Bueib Formation clarifies that the thickness increases toward the north direction of the study area and attains the greatest value of about (480m) near the JG-2 well, while it decreases toward the central and south directions reaching the lowest value of about (120 m) around the JG-9 well (Figure 3a). This reflects that the area has been uplifted during the deposition or subjected to several stages of erosion which give rise to reduction in Alam El Buieb sediments. The increase in thickness northword indicates a deep basin of deposition in the north direction. Furthermore, this map shows narrow contour lines at the central part of the study area which may denote maximum thickness, while in the other parts of the study area, the wide contour spacing may indicate that Alam El Bueib basin was possibly subsiding to the
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central with a high rate greater than the other parts. Generally from the result of Alam El Bueib isolith and facies maps, it well known that no great variations appeared in the distribution of the total contents of lithofacies. The clastic sediments are well developed at all directions (Figure 3b). 3.2. Source rock characteristics
Khatatba Formation has 48 samples which were analyzed from the JG-1well. These studied samples consist of shale, sandstone, and trace limestone. It has a TOC wt% content ranging from 0.98 to 2.28 wt% (Table 1) reflecting fair to very good (Figure 4a). The free hydrocarbon“S1” values range from 0.14 to 0.72 mg/g and “S2” values range from 0.81 to 4.74 mg/g (Table 1), indicating poor to good source potential (Figure 4b, c). The generation potential (GP) ranges from 0.96 to 5.21 mg HC/g rock (Table 1). This data indicates that the organic richness of this formation varies from poor to good GP (Peters, 1986; Hunt, 1996; Gogoi et al., 2008). The quality index of hydrocarbons (QI) ranging from 0.36 to 5.65 (Table 1) indicates mainly good indicating good for oil and gas generation (Gogoi et al., 2008). The HI and OI values for Khatatba Formation range from 79 to 243 and 30 to 397 mg/g rock, respectively (Table 1) which indicate that it is a potential source rock for generating mixed oil and gas (Figure 4d). The relation between “TOC %” and HI indicates that the oil potential of this formation is a good source (Figure 4e). The pyrolysis Tmax values for the studied samples (Table 1) indicate that the studied source rocks are immature to marginally mature for the Khatatba Formation, with the “Tmax” values ranging from 428 to 439°C (Table 1). On the other hand, the production index (PI) of this formation ranges from 0.08 to 0.33 (Table 1), revealing that the samples range between immature and mature stage. The plotting diagram (Figure 5c) shows that the relation between HI and “Tmax” values confirms that the organic matter of this formation is type III/II. Furthermore, the relation between “PI” and "Tmax” (Figure 5d) showing
Figure . Source rock charactaristics of Khatatba Formation in JG-well, North East Western Desert, Egypt.
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Table . Pyrolysis analysis measurments of Khatatba and Alam El Bueib formations in JG-well, North East Western Desert, Egypt. Depth (m)
TOC (wt.%)
S (mg/g) S (mg/g) S (mg/g)
Khatatba source rocks ,– .–. .–. .–. .– , ,– .–. .–. .–. .–. , ,– .– .–. .–. .. , ,– .–. .–. .–. .–. , ,– .–. .–. .–. .–. , ,– .–. .–. .–. .–. , ,– .–. .–. .–. .–. , ,– .–. .–. .–. .–. , ,– .–. .–. .–. .–. , Alam El Buieb source rocks , . . , . . , . . , . .
. . . .
. . . .
Tmax °C
HI (mg/g) OI (mg/g)
PI
GP
QI
–
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. . . .
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Note: TOC: total organic carbon in weight percent; S: free hydrocarbon percent in the rock (mg HC/g rock); S: residual petroleum potential (mg HC/g rock); S: releasing of organically bound CO over the temperature range (–°C). HI: hydrogen Index (mg HC/g TOC); OI: oxygen index (mg CO /g TOC). Tmax: the temperature at which the maximum pyrolytic hydrocarbon (S) liberated. PI: production index = S/S+S. S+S: generation potential (GP). S/S: hydrocarbon product type or quality index (QI).
Figure . Thermal maturity of Khatatba Formation in JG- well, North East Western Desert, Egypt.
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Figure . Source rock charactaristics of Alam El-Buieb Formation in JG- well, North East Western Desert, Egypt.
that the source rocks of Khatatba Formation is located at marginally mature approaching the main stage of hydrocarbon generation. Alam El-Bueib Formation at JG-1 well consists of high amount of shale and contain sandstones. It has TOC content ranging from 0.95 to1.65 wt% (Table 1) reflecting fair to good source rocks (Figure 6a). The Alam El Bueib Formation has “S1” values ranging from 0.31 to 0.78 mg/g (Table 1), indicating a minor variation in the volatile hydrocarbons. On the other hand, this formation is characterized by “S2” values ranging from 1.18 to 2.75 mg/g (Table 1) indicating poor to fair source potential (Peters, 1986). Figure 6b,c represents the “S1” and “S2” values versus depth for Alam El-Bueib source rocks, indicating poor to fair source potential. The GP of the studied samples range from 1.54 to 3.53 mg HC/g rock (Table 1), indicating that the organic matters have poor to fair GP. The HI values of this formation range from 85 to 212 mg/g and OI values range from 36 to 111 mg/g, respectively (Table 1), indicating that Alam El-Bueib Formation has the capability to generate gas (Figure 6d). The relation between “TOC %” and HI indicates that the oil potential of Alam El Bueib Formation is no source to good source and it shows that the potential is increased upward to be excellent source (Figure 6e). The hydrocarbon products (QI) of Alam El-Bueib Formation ranging from 0.77 to 4.61 (Table 1) indicate mainly poor to good of oil generation. Alam El-Bueib Formation has “Tmax” values ranging from 427 to 434°C (Table 1), revealing that the samples range within immature stage (Figure 7a). On the other hand, the “PI” of these formations ranges from 0.12 to 0.23 (Table 2), revealing that the source rock samples range between mature and immature stage where two samples lie within oil generation stage and two samples lie within immature stage (Figure 7b). In addition, the relation between “PI” and “Tmax” of Alam El Bueib Formation indicates that marginally mature source rock and also shows that this formation is characterized by kerogen of
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Figure . Thermal maturity of of Alam El-buieb Formation in JG-well North East Western Desert, Egypt.
type III/II (Figure 7c). The relation between PI and “Tmax” indicates that this formation is marginally mature approaching the main stage of hydrocarbon generation (Figure 7e).
Conclusions 1. The isopach map of Khatatba Formation shows that the thickness of increases toward the south western direction and decreases toward northern parts. Triangle facies map shows that the sediments consisting of sandstone and shale facies indicate a shallow marine depositional environment. Khatatba Formation bears a mature source rock and has poor-to-good generating capability for both oil and gas and gas and lie within the early generation window and oil window. 2. The isopach map of Alam El Bueib Formation increases toward the north directions, while it decreases toward the central and south parts of the study area. The facies maps show that no great variations appeared in the distribution of the total contents of lithofacies, indicating terrestrial to shallow marine depositional environment. Alam El-buieb Formation constitutes a mature source rock and has poor-to-good generating capability for both oil and gas. From the results of source rock characterization of the studied succession together with subsurface, it can be stated that Khatatba and Alam El Buieb formations are the main source rocks for hydrocarbon accumulations rich with organic matters and could be considered as effective source rocks for generating hydrocarbons in the the studied wells.
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