Subsurface Geology and Potential Capability of Oil Generation of some Jurassic and Lower Cretaceous Source Rocks in North Western Desert, Egypt.

Transcription

1 Middle East Journal of Applied Sciences, 4(2): -317, 214 ISSN: Subsurface Geology and Potential Capability of Oil Generation of some Jurassic and Lower Cretaceous Source Rocks in North Western Desert, Egypt. 1 F.S. Ramadan, 2 M.M. El Nady, 1 E.A. Eysa and 1 N.M. Abdel Wahed 1 Geology Dept, Faculty of Science, Zagazig University, Egypt. 2 Exploration Dept, Egyptian Petroleum Research Institute, Egypt. ABSTRACT The present work deals with subsurface geology, the identification of the potential and generating capability of oil generation of some Jurassic and Lower Cretaceous formations in the North Western Desert were investigated by studying the composite logs for seven wells. Jurassic units include; Ras Qattara, Khatatba and Masajid formations. Ras Qattara and Khatatba formations are not recorded in the investigated wells except at Salam-3X well. Lower Cretaceous units are represented in this work by Alam El-Bueib Formation. Isopach and lithofacies maps and lithostratigraphic correlation charts of these formations are constructed and discussed in order to distinguish the shape, the extent of sedimentary basins and the environment of deposition. Isopach maps showed that the thickness of Masajid sediments increases toward the northeastern and western directions and the thickness of Alam El-Bueib sediments increases toward the eastern and western directions. Triangle facies maps showed that limestone (non-clastic) facies are predominance in Masajid Formation reflecting open marine depositional environment and argillaceous sandstone facies are predominance in Alam El-Bueib Formation reflecting terrestrial to shallow marine depositional environment. The geochemical analysis results showed that Ras Qattara Formation constitutes a mature source rock have good very good generating capability for both oil and gas. Khatatba Formation bears a mature source rock, and has poor to good generating capability for both oil and gas. Masajid and Alam El-Bueib formations bear mature source rocks and have poor to fair generating capability for generating gas (type III kerogen). The burial history modeling shows that Ras Qattara and Khataba formations lie within the gas window, Masajid Formation lies within oil and gas windows and Alam El-Bueib Formation is still within the early stage of hydrocarbon generation. Therefore, Ras Qattara and Khatatba formations are the main source rock for hydrocarbon accumulations at Salam-3X well. Masajid and Alam El-Bueib formations are also considered as effective source rocks for generating hydrocarbons. Key words: Egypt, geochemical, subsurface, source rock, Western Desert. Introduction The Western Desert of Egypt represents an important part of the unstable shelf of the Northern Africa and comprises a total area of 7, square kilometers, 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 Qattara Depression between latitudes 31 29' and 31 52' N and longitudes 26 37' and 27 ' E (Fig. 1). The generalized stratigraphic column of the northern Western Desert includes most of the sedimentary succession from Pre-Cambrian basement complex to Recent (Fig. 2). The general structural and stratigraphical aspects of the Western Desert have been the subject of many studies, such as; Amin (1961), Said (1962 and 199), Norton (1967), Parker (1982), Meshref (1982), El-Khadragy and Sharaf (1994), Shalaby et al. (2), Zein El-Din et al. (21), El-Khadragy et al. (21) and others. Geochemical characteristics of Jurassic and Cretaceous source rocks in the Western Desert have been discussed by many authors including Matbouly (1993), Abdel Aziz (1994) and others. The main objectives of this study are: (i) trace the thickness variations, triangle facies change of the penetrated formations and assess the depositional environments of the different rock units, (ii) identify and characterize potential source rocks and their generating capability, (iii) investigate the maturation level of the proven potential source formations for oil preservation dead lines, and (iv) predict the levels of thermal maturity of the studied sequences in terms of hydrocarbon generation and expulsion. Materials and Techniques: 1) The fundamental materials which applied in this work include seven representative composite logs wells. These wells are: (Dorra-1X, Amoun-1X, Tut-1X, Tut-44, Salam-3X, Zahra-1X and Yasser-1X). Fifty nine Corresponding Author: F.S. Ramadan, Geology Dept, Faculty of Science, Zagazig University, Egypt.

2 Middle East J. Appl. Sci., 4(2): -317, representative cutting samples of argillaceous dark-grey shales and limestones, represented Jurassic rock units (Masajid, Khatatba and Ras Qattara formations) and Lower Cretaceous rock units (Alam El-Bueib Formation), were collected from Salam-3X well at different depths. The composite logs and ditch samples were supplied by Egyptian General Petroleum Corporation approval (EGPC). Pyrolysis analyses of the source rocks have been carried out in StratoChem laboratories. Fig. 1: Base map showing the drilled wells and correlation chart profile (A-A').

3 Middle East J. Appl. Sci., 4(2): -317, Fig. 2: Generalized litho-stratigraphic column of the North Western Desert (Schlumberger, 1984 and 1995). 2) Isopach and Lithofacies maps of the studied rock units were constructed using to Krumbein and Sloss (1963) technique to show the thickness and facies variation of different rock units in the study area. As well as one stratigraphic correlation chart was constructed to illustrate the subsurface geological conditions, lithostratigraphy and trends of lateral change in thickness of the studied rock units.. 3) Rock-Eval/Total Organic Carbon (TOC) analysis was carried out by a Rock-Eval II analyzer. This procedure was used by Espitalie et al. (1985), to obtain total organic carbon (TOC wt %), free hydrocarbons (S 1 = mg HC/g rock), and residual petroleum potential (S 2 = mg HC/g rock). All these parameters are used in the

4 Middle East J. Appl. Sci., 4(2): -317, present work to determine of hydrogen index (HI= mg HC/g TOC) and oxygen index (OI= mg CO 2 /g TOC), generating potential (GP= S 1 +S 2 ), type of hydrocarbons products (QI= S 2 /S 3 ). 4) Vitrinite reflectance (Ro %) measurements were made on thin section under reflected light. 5) The thermal burial history modeling was constructed using the method introduced by Lopatin (1971) that was modified and calibrated by Waples (198 and 1985) to predict the level of thermal maturity of the studied sequences in terms of hydrocarbon generation and expulsion. Results and Discussion Isopach and Facies maps: Two isopach maps are constructed for Jurassic rock units (Masajid Fm.) and Lower Cretaceous rock units (Alam El-Bueib Fm.), to demonstrate and clarify the variation and direction of thinning and /or thickening in relation to the shape of the depositional basins. As well as, triangle facies maps are constructed for studied reservoirs to illustrate the facies distribution within the basin and interpret environment conditions during Jurassic and Lower Cretaceous times. Generally, the varying proportions of sandstone, siltstone, shale and carbonate indicate different environments of sedimentation, although the limestone definitely is marine, the sandstone and shale is related to continental, fluvio-deltaic and fluviomarine or marine conditions. Masajid Formation (Upper Jurassic): Lithologically, Masajid deposits are composed of dense limestones. The isopach map shows variable thicknesses, which related to the paleotopography or the tectonic activity during the deposition of this formation. The thickness of Masajid sediments increases toward the northeastern and western directions of the study area reaching the maximum thickness (16 m) around Dorra-1X well and decreases toward the central and south directions reaching its minimum thickness (52 m) around Zahra-1X well (Fig. 3a). In the southeastern part, the wide contours spacing indicates that the rate of subsidence in this part was possibly lesser than the other parts. On the other hand, the ovate and circular patterns of isopach lines indicate that the subsidence was contemporaneous with deposition (Krumbein and Sloss, 1963). The triangle facies map shows that Masajid Formation is characterized by the predominance of limestone (non-clastic) facies at all recorded parts of the study area (Fig. 3b). The absence of clastic facies in the studied wells reflects open marine nature of the deposition of this formation. Fig. 3: Isopach (a) and triangle facies (b) maps of Masajid Formation.

5 Middle East J. Appl. Sci., 4(2): -317, Alam El-Bueib Formation (Lower Cretaceous): Alam El-Bueib Formation lithologically consists of sandstones interbeded with shales and thin carbonate beds (limestones and dolomites). The isopach map shows the variation in thickness of Alam El-Bueib Formation through the different studied wells. The thickness increases toward the east and western direction and attains the greatest value of about 982 m around Dorra-1X well at the northeastern part, while it decreases toward the central and southwestern parts of the study area (Fig. 4a). This formation is completely disappeared in Amoun- 1X well, Tut-44 well and Yasser-1X well. This reflects that the area has been uplifted during the deposition or subjected to several stages of erosion which give rise to reduction in thickness of Alam El-Bueib sediments. The increase in thickness at the western direction indicates a deep basin of deposition. Triangle facies map of Alam El-Bueib Formation reflects uniformity in lithology. It is characterized by the predominance of argillaceous sandstone facies at all parts of the study area except at Amoun-1X, Tut-44 and Yasser-1X wells where no deposition took place at these wells (Fig. 4b). Non-clastic facies are not recorded on the studied wells. These facies indicate terrestrial to shallow marine depositional environment. Fig. 4: Isopach (a) and triangle facies (b) maps of Alam El-Bueib Formation. Lithostratigraphic Cross Section: The lithostratigraphic correlation chart illustrates the change in lithologic characters or any break in the depositional continuity. This section shows the equivalency of stratigraphic units, and exhibits thickness variation. Borehole data from three composite logs are used to construct one correlation chart AA' in the NW- SE direction (Fig. 1). This lithostratigraphic cross section A-A' (Fig. 5) extends along NW-SE direction and passes through Tut- 1X, Salam-3X and Zahra-1X wells. It shows that Lower and Middle Jurassic rock units (Ras Qattara and Khatatba formations) are not easily to be correlated. Cretaceous rock units are well corellated (Fig. 5) where they are represented at all studied wells. The disappearance of Ras Qattara and Khatatba formations at Zahra-1X well may be because the drilling stopped, non-deposition of basin in this area. The thickness of Masajid Formation (Upper Jurassic) relatively decreases toward the southeast direction reaching the lowest thickness at Zahra-1X well. Alam El-Bueib Formation (Lower Cretaceous) shows a variation in thickness from well to another. Its maximum thickness is present at Tut-1X well and the minimum thickness is found at Salam-3X well. Alamein and Dahab formations (Lower Cretaceous) are nearly homogenous in their thickness at all the correlated wells. The thickness of Kharita Formation (Lower Cretaceous) is relatively variable from well to another. Its maximum thickness is located at Tut-1X well and the minimum thickness is occurred at Salam-3X well. As well as, Bahariya Formation (Upper Cretaceous) relatively differs from well to another. Its maximum thickness is at Salam-3X well and its minimum thickness is at Zahra-1X well. Also, the chart shows that the thickness of Abu Roash Formation (Upper Cretaceous) relatively decreases toward the southeast direction reaching the lowest thickness at Zahra-1X, while the thickness of Khoman Formation (Upper Cretaceous) relatively increases toward the southeast direction reaching the greatest thickness at Zahra-1X.

6 Middle East J. Appl. Sci., 4(2): -317, Fig. 5: Lithostratigraphic correlation chart along the profile (A-A'). Source rock characteristics: The potentiality and generating capability source rocks for oil generation is evaluated by measuring of total organic carbon (TOC), pyrolysis derived (S 1, S 2 ) (Waples, 1985), Rock-Eval temperature pyrolysis (T max ), production index (PI) and vitrinite reflectance (R o %) of the rock samples. Peters (1986) reported that the samples which contain TOC less than.5 wt %, S 1 less than.5 mg/g and S 2 less than 2.5 mg/g are considered poor source rocks. Samples contain from.5 to 1. wt % TOC, S 1 from.5 to 1. mg/g and S 2 from 2.5 to 5 mg/g are fair source rocks. Meanwhile, those containing TOC from 1-2 wt %, S 2 from 1-2 mg/g and S 2 from 5-1 mg/g are good source rocks and samples that contain more than 2 wt % TOC, S 1 more than 2 mg/g and S 2 >1 mg/g are considered very good source rocks. The generation potential (GP), is identified by using the sum of S 1 +S 2 obtained from pyrolysis analysis. The type of hydrocarbons products (QI) such as oil and gas generated from a source rock by using the ratio of the values S 2 and S 3 derived from pyrolysis analysis. Ratio of S 2 /S 3 is proportional to the amount of hydrogen in a source rock and is an indicator of the potential to generate oil and gas (Hunt, 1996). Peters (1986) stated that the geochemical parameters describing source rock generative potential and reported that the samples which contain QI (=S 2 /S 3 ) less than 1 are considered poor source rocks. Samples contain from 1 to 5 QI indicating a potential

7 Middle East J. Appl. Sci., 4(2): -317, source for generating gas, and samples contain QI from 5 to 1 indicating a potential source for generating oil and gas. Meanwhile, those containing QI more than 1 indicating a potential source for generating oil. Waples (1985) used the hydrogen index values (HI) to differentiate between the types of organic matter. Hydrogen index below about 15 mg/g indicate a potential source for generating gas (mainly type III kerogen). Hydrogen index between 15- mg/g contain more type III kerogen than type II and therefore are capable for generating mixed gas and oil but mainly gas. Kerogen with hydrogen index above mg/g contain substantial amount of type II macerals and thus are considered to have good source potential for generating oil and minor gas. Kerogen with hydrogen index above 6 mg/g usually consists of nearly type I or type II kerogen, they have excellent potential to generate oil. Peters, 1986; Espitalie et al., 1985 and Bordenove et al., 1993, reported that oil generation from source rocks began at T max from 435 o C to 465 o C, vitrinite reflectance (R o %) between.5 to 1.35 % and production index (PI) between.2 to.4, the organic matters are in immature stage when T max has a value less than 435 o C, R o % less than.5 % and PI less than.2 and the gas generation from source rocks began at T max 47 o C, R o % more than 1.35 % and PI more than.4. Ras Qattara Formation (Lower Jurassic): Ras Qattara Formation has total organic carbon content (TOC wt %) ranging from 1.22 wt % to 3.86 wt % (Table 1) indicating good to very good source rocks. The TOC values follow the contouring pattern as indicated by TOC versus depth (Fig. 6a). The pyrolysis-derived (S 1 and S 2 ) values of Ras Qattara samples range from.36 to 6.36 mg/g and 1.63 to 7.71 mg/g, respectively (Table 1), indicating poor to good generating potential (Peters, 1986). The S 1 and S 2 values follow the same contouring pattern as the organic richness as indicated by the generating potential graph (Fig. 6 b,c). Table 1: Pyrolysis analysis and vitrinite reflectance measurments of the studied source rocks in Ras Qattara Formation. Depth ( ft ) T.O.C (wt. %) S 1 S 2 S 3 T max ( C ) R o % PI S 1+S 2 S 2/S 3 HI OI Note: TOC: Total Organic Carbon in weight percent; S 1: Free hydrocarbons percent in the rock (mg HC/g rock); S 2: Residual petroleum potential (mg HC/g rock); S 3: Releasing of organically bound CO 2 over the temperature range ( 55 o C). HI: Hydrogen Index (mg HC/g TOC); OI: Oxygen Index (mg CO2/g TOC). T max: The temperature at which the maximum pyrolytic hydrocarbon (S 2) liberated. R o (%): Vitrinite reflectance measurements. PI: Production Index = S 1/S 1+S 2. S 1+S 2: Generation Potential (GP). S 2/S 3: hydrocarbons products type or Quality Index (QI). The generation potential (GP) ranging from 3.4 to mg HC/g (Table 1). This data of Ras Qattara Formation indicates that the organic matters are rated from poor to good generation potential (Ghori and Haines, 27). The type of hydrocarbons products (QI) such as oil and gas generated from a source rock, is obtained by using the ratio of S 2 /S 3. The type of hydrocarbons products (QI) of Ras Qattara Formation ranging from 1.44 to (Table 1) indicating that this formation is mainly good source for oil generation. For Ras Qattara Formation the hydrogen index and oxygen index range from 12 to 252 mg/g and 15 to 88 mg/g (Table 1). The relationship between the Hydrogen Index (HI) and Oxygen Index (OI) reflects that this formation has a potential source rock for generating mixed oil and gas (type III/II of kerogen), (Fig. 7a). The relation between TOC % and HI indicates that the oil potential of this formation is no source to poor source and it show that the potential is increased upward to be good source (Mann. et al., 29) (Fig. 7b).

8 Middle East J. Appl. Sci., 4(2): -317, TOC (wt %) S 1 (mg/g) S 2 (mg/g) Fig. 6: Source rock charactaristics of Ras Qattara Formation at Salam-3X well (Peters, 1986). Hydrogen Index ( mg HC / g TOC ) TOC (wt %) Fig. 7: Hydrogen index versus Oxygen index (a, Van Krevelen, 1961 modified by Espitalie et al, 1977) and total organic carbon (b, Mann et al., 29), show type of source rocks of Ras Qattara Formation. Ras Qattara Formation has T max values range from 44 o C to 454 o C (Table 1) indicating that the samples lie within oil generation stage (Fig. 8a) and R o % values range from.87 to 1.57 % (Table 1) indicating that the source rocks are mature where the majority of samples lie within oil generation stage except two samples lie within gas generation stage (Waples, 198 and 1985) (Fig. 8b). On the other hand, the production index (PI) of this formation ranges from.11 to.46 (Table 1) revealing that the samples lies within gas generation stage and oil generation stage (Fig. 8c). In addition, the relation between hydrogen index (HI) and T max values confirms that Ras Qattara Formation is mature (oil generative) source rock and also shows that the organic matter of this formation ranges between type III and type III/II (Fig. 9a). Furthermore, the relation between PI and T max (Fig. 9b), it is indicated that Ras Qattara Formation is mature approaching to the main stage of hydrocarbon generation (Waples, 1985). Khatatba Formation (Middel Jurassic): Khatatba Formation has content of TOC wt % ranging from.5 wt % to 5.1 wt % (Table 3) reflecting that Khatatba source rocks are variegated mainly from fair to very good source rocks (Fig. 1a). The studied samples

9 Hydrogen Index ( mg HC / g TOC ) Middle East J. Appl. Sci., 4(2): -317, of Khatatba Formation are characterized by S 1 and S 2 values range from.14 to 1.59 and.35 to 9.59 mg/g, respectively (Table 2) reflecting poor to good source potential (Fig. 1b,c). The generation potential (S 1 +S 2 ) of Khatatba Formation ranging from.18 to mg HC/g rock (Table 2) revealing the organic richness of this formation varies from poor to good. The type of hydrocarbons products (S 2 /S 3 ) ranging from.31 to (Table 2) indicates mainly fair to good of oil generation R o (%) Production Index Fig. 8: Thermal maturity of of Ras Qattara Formation at Salam-3X well (Peters, 1986) Production Index Fig. 9: Relationship between T max and Hydrogen Index (a, Espitalie et al, 1985) and Production Index (b, Peters, 1986) of Ras Qattara Formation at Salam-3X well. The hydrogen index (HI) values of Khatatba Formation range from 53 to 174 mg/g, and OI (oxygen index) values range from 1 to 27 mg/g (Table 3). The relationship between the HI and OI indicates that the organic matter classified as type III/II kerogen (mixed type) (Fig. 11a). The relation between TOC % and HI indicates that the oil potential of this formation is poor to good source and it shows that the potential increases upward to be good source (Fig. 11b).

10 Middle East J. Appl. Sci., 4(2): -317, Table 2: Pyrolysis analysis and vitrinite reflectance measurments of the studied source rocks in Khatatba Formation. Depth ( ft ) T.O.C (wt. %) S 1 S 2 S 3 T max ( C ) R o % PI S 1+S 2 S 2/S 3 HI OI TOC (wt %) S 1 (mg/g) S 2 (mg/g) Fig. 1: Source rock charactaristics of Khatatba Formation at Salam-3X well (Peters, 1986). The maturity parameters of Khatatba Formation as indicated by T max values ranging from 435 to 455 o C, vitrinite reflectance R o % measurements ranging from.65 to 1.67 % and production index (PI) of this formation ranges from.14 to.6 (Table 2) indicating that the studied samples lie in between within oil and gas generation stages (Fig. 12 a-c). Moreover, the cross plot of the pyrolysis T max and hydrogen index (HI) (Fig. 13a) revealing that type III kerogene of organic matters of Khatatba Formation and lie in mature stage of oil zone. The relation between PI and T max (Fig. 13b), indicates that the source rock of Khatatba Formation is mature approaching to the main stage of hydrocarbon generation.

11 Hydrogen Index ( mg HC / g TOC ) Hydrogen Index ( mg HC / g TOC ) Middle East J. Appl. Sci., 4(2): -317, Oxygen Index (mg CO 2 / g TOC) TOC (wt %) Fig. 11: Hydrogen index versus Oxygen index (a, Van Krevelen, 1961 modified by Espitalie et al, 1977) and total organic carbon (b, Mann et al., 29), show type of source rocks of Khatatba Formation R o ( %) Production Index Fig. 12: Thermal maturity of of Khatatba Formation at Salam-3X well (Peters, 1986). Masajid Formation (Upper Jurassic): The content of TOC wt % of Masajid Formation ranges from.6 to1.2 wt % (Table 3) revealing that the organic richness of this formation varies from poor to fair (Fig. 14a). This indicates that the organic matters of Masajid Formation are deposited in intermediate between oxidizing and reducing, where preservation of lipidrich organic matter with limited and substantial source potential (Gogoi et al., 28). The pyrolysis-derived (S 1 and S 2 ) values of Masajid Formation range from.48 to.91 mg/g and.68 to 1.37 mg/g, respectively (Table 3), indicating poor to fair generating source potential. The representation of S 1 and S 2 values (Fig. 14b,c) confirms that the generating potential of the source rocks of this formation is rated from poor to fair. The generation potential (S 1 +S 2 ) of Masajid Formation ranging from 1.21 to 2.28 mg HC/g rock (Table 2) revealing that the organic richness of this formation varies from poor to fair. The type of hydrocarbons products (S 2 /S 3 ) ranging from.32 to.85 (Table 2) indicates mainly fair for oil generation. The hydrogen index (HI) values of Masajid Formation ranging from 11 to 134 mg/g and oxygen index (OI) ranging from 148 to 382 mg/g, (Table 3). The relationship between the Hydrogen Index (HI) and Oxygen Index (OI) suggests a potential to generate type III kerogen as shown in Van Krevelen type diagram (Fig. 15a).

12 Hydrogen Index ( mg HC / g TOC ) Middle East J. Appl. Sci., 4(2): -317, The relation between TOC wt % and hydrogen index (HI) indicates that the oil potential of this formation is poor to good source and it shows that the potential is increased upward to be good source (Fig. 15b) Production Index Fig. 13: Relationship between T max and Hydrogen Index (a, Espitalie et al, 1985) and Production Index (b, Peters, 1986) of Khatatba Formation at Salam-3X well. Table 2: Rock Eval pyrolysis and vitrinite reflectance measurments of Masajid Formation. Depth T.O.C S 1 S 2 S 3 T max R o % PI S 2+S 3 S 2/S 3 HI OI (ft) (wt. %) ( C ) TOC (wt %) S 1 (mg/g) S 2 (mg/g) Fig. 14: Source rock charactaristics of Masajid Formation at Salam-3X well (Peters, 1986). Masajid Formation (Upper Jurassic) has T max values range from 43 o C to 441 o C (Table 3) reflecting that the samples lie in between marginally mature to mature stage (Fig. 16a). The vitrinite reflectance measurements of Masajid Formation, ranging from.59 to 1.1 % (Table 3), place this formation within the early stage of hydrocarbon generation to oil window (Fig. 16b), where the source rocks are considered as mature source rock.

13 Hydrogen Index ( mg HC / g TOC ) Hydrogen Index ( mg HC / g TOC ) Middle East J. Appl. Sci., 4(2): -317, Production index (PI) of this formation ranges from.36 to.51 (Table 3) indicating that the samples lie in between within oil generation and gas generation stages (Fig. 16c). Moreover, the cross plot of the pyrolysis T max and hydrogen index (HI) (Fig. 17a) reveals type III kerogene of organic matters and lie in mature stage of oil zone. The relation between PI and T max (Fig. 17b), indicates that the source rock of Masajid Formation is marginally mature approaching to the main stage of hydrocarbon generation Oxygen Index (mg CO 2 / g TOC) TOC (wt %) Fig. 15: Hydrogen index versus Oxygen index (a, Van Krevelen, 1961 modified by Espitalie et al, 1977) and total organic carbon (b, Mann et al., 29), show type of source rocks of Masajid Formation R o (%) Production Index Fig. 16: Thermal maturity of of Masajid Formation at Salam-3X well (Peters, 1986). Alam El-Bueib Formation (Lower Cretaceous): The organic richness (TOC wt %) of Alam El-Bueib Formation samples varies from.53 to.98 wt % indicating poor to good source rocks (Fig. 18a) (Table 4). This TOC wt % values are associated with depositional environments intermediate between oxidizing and reducing, where preservation of lipid-rich organic matter with limited source and substantial source potential (Gogoi et al., 28). The pyrolysis-derived S 1 and S 2 values of Alam El-Bueib Formation samples range from.55 to.97 mg/g and.6 to 1.41 mg/g, respectively (Table 4), indicating poor to fair generating potential (Peters, 1986). The S 1 values follow the same contouring pattern as the organic richness as indicated by the generating potential map (Fig. 18b, c). However few samples are rated as a good potential and all the other samples have poor to fair generating capability; these

14 Hydrogen Index ( mg HC / g TOC ) Middle East J. Appl. Sci., 4(2): -317, samples may be contaminated before analysis as they have high production index (PI) from.36 to.57 (Fig. 18) Production Index Fig. 17: Relationship between T max and Hydrogen Index (a, Espitalie et al, 1985) and Production Index (b, Peters, 1986) of Masajid Formation at Salam-3X well TOC (wt %) S 1 (mg/g) S 2 (mg/g) Fig. 18: Source rock charactaristics of Alam El-Bueib Formation at Salam-3X well (Peters, 1986). The generation potential (GP), is identified by using the sum of S 1 +S 2 obtained from pyrolysis analysis. The generation potential (S 1 +S 2 ) of the studied samples range from 1.15 to 2.21 mg HC/g rock (Table 4) indicates that the organic matters are poor to fair generation potential (Ghori and Haines, 27). Table (4) shows that the hydrocarbon products S 2 /S 3 of Alam El-Bueib Formation ranging from.45 to 1.86 indicate mainly fair of oil generation. The hydrogen index (HI) values of the Alam El-Bueib Formation range from 16 to 144 mg/g and oxygen index (OI) values range from 78 to 248 mg/g (Table 4). The relationship between the Hydrogen Index (HI) and Oxygen Index (OI) suggests a potential to generate type III kerogen as shown in Van Krevelen type diagram (Fig. 19a). The relation between TOC wt % and hydrogen index (HI) (Fig. 19b) indicates that the oil potential of this formation is no source to poor source and it show that the potential is increased upward to be good source (Mann. et al., 29).

15 Hydrogen Index ( mg HC / g TOC ) Middle East J. Appl. Sci., 4(2): -317, Hydrogen Index ( mg HC / g TOC ) Oxygen Index (mg CO 2 / g TOC) TOC (wt %) Fig. 19: Hydrogen index versus Oxygen index (a, Van Krevelen, 1961 modified by Espitalie et al, 1977) and total organic carbon (b, Mann et al., 29), show type of source rocks of Alam El-Bueib Formation. Alam El-Bueib Formation (Lower Cretaceous) has T max values range from 432 o C to 437 o C (Table 4) reflecting that the samples lie in mature stage (Fig. 2a), and vitrinite reflectance measurements range from.65 to 1.29 % (Table 4) which places this formation within the oil window as it is considered as mature source rock (Fig. 2b), (Waples, 198 and 1985). Production index (PI) of this formation ranges from.36 to.57 (Table 4) indicating that the samples lie in lie in between within oil generation and gas generation stages (Fig. 2c). Moreover, the cross plot of the pyrolysis T max and hydrogen index (HI) (Fig. 21a) confirms that Alam El- Bueib Formation lies in mature stage and is characterized by kerogen of type III. From the relation between PI and T max (Fig. 21b), it indicates that this formation is marginally mature approaching to the main stage of hydrocarbon generation (Waples, 1985) R o ( %) Production index Fig. 2: Thermal maturity of of Alam El-Bueib Formation at Salam-3X well (Peters, 1986). Timing of Petroleum Generation: In the present study, the burial history model of the different hydrocarbon bearing rock units in Salam-3X well was constructed to predict the maturity of the source rock, timing of hydrocarbon generation, expulsion and migration (Fig. 22). The oil window in this work is defined as the depth interval between peak of hydrocarbon generation (R o =.85 %) and the oil floor (R o = 1.35 %) according to Waples (198 and 1985).

16 Hydrogen Index ( mg HC / g TOC ) Middle East J. Appl. Sci., 4(2): -317, Burial modeling (Fig. 22) shows that Ras Qattara Formation entered to the early stage of hydrocarbon generation during Early Cretaceous time at 1 Mybp (million years before present). It reached to the oil window during Late Cretaceous time at 92 to 72 Mybp and entered to the gas generation at 76 Mybp during Late Cretaceous till present time. Khatatba Formation started to generate hydrocarbons during Cretaceous time at 93 to 76 Mybp as indicated by the thermal burial history model (Fig. 22). It reached to the oil window (peak of hydrocarbon generation) during Late Cretaceous at 9 Mybp till Eocene time at 42 Mybp and reached to the gas generation at 72 Mybp during Late Cretaceous till present time. Khatatba Formation bears a mature source rock with good generating capability for both oil and gas. Masajid Formation entered to the early stage of hydrocarbon generation at 9 Mybp (million years before present) during Early Cretaceous time. It reached to the oil window to during Late Cretaceous time at 75 Mybp till Oligocene time at 35 Mybp and entered to the gas generation at 4 Mybp during Eocene till present time (Fig. 22). Meanwhile, Alam El-Bueib Formation reached to the early stage of hydrocarbon generation during Late Cretaceous time at 88 Mybp till present time. Also, it entered to the peak of hydrocarbon generation during Late Cretaceous time at 73 Mybp till present time and reached to the gas generation during Oligocene time at 34 Mybp till present time (Fig. 22) Production index Fig. 21: Relationship between T max and Hydrogen Index (a, Espitalie et al, 1985) and Production Index (b, Peters, 1986) of Alam El-Bueib Formation at Salam-3X well. Conclusions: 1. The isopach map showed that the thickness of Masajid sediments increases toward the northeastern and western directions. Triangle facies map of Masajid Formation showed that limestone (non-clastic) facies are predominance in this formation reflecting open marine depositional environment. In addition, the isopach map showed that the thickness of Alam El-Bueib sediments increases toward the eastern and western directions. Moreover, triangle facies map of Alam El-Bueib Formation showed that argillaceous sandstone facies are predominance in this formation reflecting terrestrial to shallow marine depositional environment. 2. The lithostratigraphic correlation chart illustrated that Jurassic formations, except Masajid one, are not easily correlated through the correlated wells, while Cretaceous formations are easily correlated where they are well represented at all the correlated wells. Also, it shows that the thickness of Kharita and Abu Roash formations relatively increases toward the north direction while, the thickness of Khoman Formation relatively increases toward the south direction. This may be due to tectonic regime prevailing in the area. 3. Ras Qattara Formation constitutes a mature source rock has good very good generating capability for both oil and gas. 4. Khatatba Formation bears a mature source rock, and has poor to good generating capability for both oil and gas. 5. Masajid and Alam El-Bueib formations bears a mature source rocks and have poor to fair generating capability for generating gas (type III kerogen). 6. The burial history modeling of the sedimentary section shows that Ras Qattara and Khataba formations lie within the gas window, Masajid Formation lies within oil and gas windows, and Alam El-Bueib Formation is still within the early stage of hydrocarbon generation.

17 Middle East J. Appl. Sci., 4(2): -317, Therefore, Ras Qattara and Khatatba formations are the main source rock for hydrocarbon accumulations at Salam-3X well. Masajid and Alam El-Bueib formations are also considered as effective source rocks for generating hydrocarbons. Fig. 22: Burial history model for Salam-3X well in the North Western Desert, Egypt. References Abdel Aziz, A.L., Jurassic source rock maturity and thermal history modeling of the Khalda west area, North Western Desert Egypt. EGPC 12 th Petrol. Explor. and Prod. Conf., Cairo, Egypt, 2: Amin, M.S., Subsurface features and oil prospects of the Western Desert, Egypt. 3 rd Arab. Petrol. Cong., Alexandria, Egypt, pp: 2-8. Bordenove, M.L., J. Espitalie, P. Leplat, J.L. Oudin and M. Vandenbrouke, Screening techniques for source rock evaluation. In: Bardenove (ed.), Applied Petrol. Geochem., Paris Editions Technip., pp: El-khadragy, A.A. and M. Sharaf, Inferring the basement structure of northwestern Desert, using potential field data. Bull. Fac. Sci., Zagazig Univ., 16(2): El-khadragy, A.A., M.H. Saad and A. Azab, 21. Crustal modeling of south Sitra area, north Western Desert, Egypt using Bouguer gravity data. Journal of Applied Science Research, 61(1): Espitalie, J., G. Deroo and F. Marquis, Rock-Eval pyrolysis and its application. Rev. Inst. Fr. Petrol, 4:

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