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Organic Geochemistry of Source Rocks, Condensates, and ThermalGeochemical Modeling of Miocene Sequence of Some Wells, Onshore NileDelta, EgyptM. M. El Nadya

a Egyptian Petroleum Research Institute (EPRI), Nasr City, Cairo, Egypt

To cite this Article Nady, M. M. El(2007) 'Organic Geochemistry of Source Rocks, Condensates, and Thermal GeochemicalModeling of Miocene Sequence of Some Wells, Onshore Nile Delta, Egypt', Petroleum Science and Technology, 25: 6, 791— 818To link to this Article: DOI: 10.1080/10916460600803629URL: http://dx.doi.org/10.1080/10916460600803629

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Petroleum Science and Technology, 25:791–818, 2007

Copyright © Taylor & Francis Group, LLC

ISSN: 1091-6466 print/1532-2459 online

DOI: 10.1080/10916460600803629

Organic Geochemistry of Source Rocks,

Condensates, and Thermal Geochemical Modeling

of Miocene Sequence of Some Wells,

Onshore Nile Delta, Egypt

M. M. El Nady

Egyptian Petroleum Research Institute (EPRI), Nasr City, Cairo, Egypt

Abstract: The organic geochemical and biomarker analyses of the Miocene source

rocks of some wells in the onshore Nile Delta, suggested that the Abu Madi For-

mation has poor immature to marginally mature source rocks of Type III Kerogen

deposited under the terrestrial environment. The Sidi Salem Formation has fair-to-

good mature source rocks of producing mixed oil and gas, originating mainly from

marine organic sources. The Moghra Formation has mature good source rocks for

Type (II/III) kerogen, derived from organic matter and rich in both terrigeneous and

marine sources. The geochemistry of condensates revealed that the Abu Madi and

Moghra condensates originated from marine organic matters with little input from a

terrestrial source, while Sidi Salem condensate was derived from more contribution of

terrestrial organic matters. Abu Madi condensate is less mature than Sidi Salem and

Moghra condensate. The geochemical thermal modeling of the Miocene source rocks

indicates that the Abu Madi formations are in the early stages of hydrocarbon up until

the present time, while Moghra and Sidi Salem formations are in the mature stage

of hydrocarbon generation up until the present time. This indicates that the studied

condensates have probably migrated from deeply buried source rocks which are at a

higher level of maturity rather than from less mature source rocks in the study area.

Keywords: condensates, Egypt, onshore Nile Delta, source rocks, thermal geochem-

ical models

INTRODUCTION

The Nile Delta is a triangular shape that covers an onshore area of about

25,000 square kilometers and about an equal offshore area to 200 meters. The

southern apex of the Delta is at 30ıN, some 30 kilometers north of Cairo.

Address correspondence to Dr. Mohamed M. El Nady, Egyptian Petroleum Re-

search Institute, Department of Exploration, Organic Geochemistry Unit, Nasr City,

Hai Al-Zehour 11727, Cairo, Egypt. E-mail: [email protected]

791

Downloaded By: [University of Technology, Sydney] At: 11:27 19 December 2010

792 M. M. El Nady

The Nile Delta basin contains a thick sequence of potential hydrocarbon

source rocks that generate essentially gas and condensates.

Although the Nile Delta has been predominantly considered an important

gas province, the analyses of potential source rocks in the Miocene have

identified oil in a number of wells, which may indicate the possible presence

of commercial oil occurrence (Abdel Halim, 2001). More than 160 wells

have been drilled in the Delta during the last few years. The area of study

covers the onshore concession within the Nile Delta, which lies between

longitude 30ı30

0 to 31ı30

0 E and latitude 31ı00

0 to 31ı30

0 N (Figure 1). The

Egyptian General Petroleum Corporation (EGPC) (1994) suggests that the

Oligocene-Miocene sediments include the best source rocks in the northern

Delta as indicated from total organic carbon (TOC) and Rock-Eval pyrolysis

data. The thickness of sandstones in Moghra, Sidi Salem, and Abu Madi

formations in the study area have proven to be the most suitable reservoir

units (EGPC, 1994).

The main objective of this article is to evaluate the potential of the

Miocene source rocks in the onshore Nile Delta (Figure 1). There is discussion

of the organo-geochemical characteristics of Miocene source rocks and some

condensates to identify their origin and maturation on the basis of biological

marker characteristics. This target has been achieved throughout the pyrolysis

analysis of 32 shaly samples from wells (Abu Madi-1, 3, 5; Qawasim-1;

Abadiya-1; and Kafer El Sheikh-1; Figure 1) representing Miocene source

rocks (Abu Madi, Sidi Salem, and Moghra formations) in the study area. Gas

chromatography (GC) and gas chromatography-mass spectrometry (GC/MS)

analysis of the representative samples from source rocks and condensates

Figure 1. Location map of the studied wells, onshore Nile Delta, Egypt.


Organic Geochemistry in Nile Delta 793

of Abu Madi, Sidi Salem, and Moghra formations were done. Four thermal

geochemical modeling and maturity profiles were constructed to assess the

petroleum accumulation in the study area. The samples were provided to the

author by the authorities of the EGPC.

The geochemical studies of the Nile Delta have been discussed by Zein

El Din et al. (1988); Abu El-Ella (1990) suggested that the highest levels

of source rock maturity occur in the northern part of the onshore around

Abu Madi wells. Halim et al. (1996) concluded that the Nile Delta gases are

thermogenic and are mainly sources from Type II kerogen. Metwalli (2000)

concluded that biogenic and nonbiogenic sources for natural gas have been

identified for a number of on- and offshore wells in the Nile Delta. Hammad

(2000) classified the Sidi Salem Formation into two system tracts based on

the specific organo-geochemical characteristics. The first one is a low stand

system (tract) formed of onlapping submarine conditions. The second is a

high stand system deposited under shallow marine conditions.

EXPERIMENTAL

A Rock-Eval/TOC analysis was conducted using a LECO CR 12 organic

analyzer connected to a Rock-Eval II pyrolysis which was performed to obtain

TOC, S1, S2, S3, and Tmax data (see Peters, 1986).

A gas chromatographic analysis of the saturated hydrocarbon fractions

of the source rocks and condensates was achieved by a Perkin Elmer Instru-

ment Model 8700 provided with a flame ionization detector (FID). The oven

temperature was programmed for 100 to 320ıC at 3ıC/min and a final time

of 20 min. A SPB-1 capillary column of 60 m in length and nitrogen was

used as a carrier gas. The optimum flow rate was 6 ml/min.

A gas chromatography-mass spectrometry used a 50 m � 0.25 mm fused

silica capillary column of bonded SE 54 installed with a finnigan MAT TSQ-

70 combined gas chromatography/quadrupole mass spectrometer. The column

oven was programmed from 100 to 310ıC at 4ıC/min. Biomarker identifica-

tion was achieved using mass fragmentograms of characteristic ions (Philp,

1985; Philip and Gilbert, 1986; Peters and Moldowan, 1993).

Pyrolysis and gas chromatographic analyses of the source rocks were

done in the laboratories of the Egyptian Petroleum Research Institute (EPRI).

Gas chromatography-mass spectrometric analyses of the source rocks and

condensates were done in the laboratories of the StratoChem (Cairo) and

provided to the author by the authorities of the EGPC.

GEOLOGY OF THE NILE DELTA

The geology of the Nile Delta is synthesized by Salem (1976) and Said

(1990). It is generally agreed, however, that the history of the Delta is still


794 M. M. El Nady

only partially understood. The oldest sedimentary rocks penetrated in the Nile

Delta are the shallow marine Late Jurassic carbonates, which are overlaid un-

conformably by Early Cretaceous sediment. The Late Cretaceous interbedded

carbonate-clastic sequence unconformably underlies the earliest Tertiary sedi-

ments, which is unconformably overlaid by the Late Eocene-Early Oligocene

shale section (prone source rocks). The Late Oligocene-Early Miocene sec-

tion is of sandy facies. The Middle-to-Late Miocene sediments are the main

hydrocarbon reservoirs in the Nile Delta. The Early Pliocene formations were

deposited in a deep marine, outer neritic environment. Rizzini et al. (1978)

recognized that the clastic sediments in the onshore Nile Delta can be grouped

into three sedimentary cycles: a Miocene cycle, comprising largely nonma-

rine to shallow marine deposited of the Sidi Salem, Qawasim, and Abu Madi

formations, a Palio-Pleistocene cycle, comprising the open marine Kafr El

Sheikh formation, and a Holocene cycle of the deltaic El Wastani, Baltim,

and Mit Ghamr/Bilgas formations. El-Heiny and Enani (1996) recognized

six depositional sequences and nine system tracts in the Late Oligocene-

Early Pliocene section in the North Nile Delta. Each sequence was separated

into low stand system tracts, which represented marine turbiditic onlap and

upper high stand system tracts, which were characterized by high stand shelf

progression and gave rise to downlap surface changing into a marine hiatus

of deposition in a condensed section basin ward.

The Miocene sedimentary section penetrated by wells in the study area

(Figure 2) consists of thick shales with some sandstones and anhydrite. The

following stratigraphic unite are recognized.

Abu Madi and/or Qawasim Formation (Late Miocene)

It is grade into Rosetta Formation in the offshore toward the northwest, which

consists of anhydrite, shales, and some sandstones facies. These formations

overlain unconformably by the Kafer El Sheikh Formation and underlain

unconformably by the Sidi Salem formation (Figure 2).

Sidi Salem Formation (Middle Miocene)

It is dominated by shales with some sandstones facies, deposited under marine

to fluvial condition. It is unconformably underlain by Moghra formation and

unconformably overlain by Qawasim and/or Abu Madi formations.

Moghra Formation (Early Miocene)

It is composed of calcareous marine shales and sandstones overlain uncon-

formably by the Sidi Salem Formation.

The Nile Delta region is divided into two subprovinces: the South

Nile Delta block and the North Nile Delta basin separated by flexure zone



Figure 2. Generalized stratigraphic column of the Nile Delta, Egypt (El-Heiny, 1982;

modified after El-Heiny and Morsi, 1992).

(Zaghloul, 1976; Zaghloul et al., 1979). The South Delta block is charac-

terized by a gradual northward dip of top Middle Eocene carbonates. The

North Delta basin is characterized by two main structure patterns, deep pre-

Tortonian, and shallow post-Meissinian fault patterns. Zaghloul et al. (2001)

recognized that the Nile Delta basin seemed to have been initiated by struc-

tures occurring in the Mesozoic and Cenozoic times in successive tectonic

events that took place since the Paleozoic onward and mainly including the

following:


796 M. M. El Nady

1. E-W shears in the Mesozoic times and rejuvenated during the Tertiary.

2. NE-SW Palusium shear during the Triassic-Jurassic time onward associ-

ated with opening of the Tethys.

3. E-NE Syrian Arc movements in the Late Cretaceous-Early Tertiary asso-

ciated with closure of the Tethys.

4. Tertiary transform faults including the NNW Gulf of Suez-Red Sea rift,

the NNE Aqaba rift, and the N-S Baltim rift in addition to the offshore NE

Rosetta and the NE Temsah faults. These faults are mostly rejuvenated of

pre-Tertiary structures.

RESULTS AND DISCUSSION

Geochemistry of Source Rocks

Abu Madi Formation (Late Miocene)

Abu Madi Formation in the studied part of the onshore Nile Delta has TOC

values ranging from 0.39 to 2.34 wt% (Table 1). The pyrolysis “S2” value

of 0.88 to 2.10 mg HC/g rock (Table 1). These data indicate poor source

rocks (Figures 3A and B). The hydrogen index values (HI) range from 25

to 250 mg HC/g TOC (Table 1), revealing that the organic matter can be

classified as Type III Kerogen (mainly gas prone) (Figure 3C). The source

rocks in Abu Madi Formation has Tmax values ranging from 430 to 435ıC

(Table 1) indicating immature to marginally mature source rocks (Figure 3D).

The gas chromatograms of Abu Madi Formation (Figure 4A) show that

pristane is greater than phytane with a pristane/phytane ratio (1.33), pristane/n-

C17 and phytane/n-C18 ratios (0.67 and 0.55, respectively, Figure 4A), nor-

mal alkane distribution is in the range of n-C15 to n-C25 with a slightly

odd carbon preference at n-C19-n-C30 range (Figure 4A). The presence of X

compound and C29 normoretane, C30 moretane, and C30 hopane (Figure 4B)

suggest terrestrial organic sources. High bacterial contribution and limited

input from marine organic matters in anoxic environments are indicated by

a moderate concentration of C29 norhopane, slightly low tricyclic terpanes,

and low gammacerane and C35 homohpanes (Figure 4B) (Guzman-Vega and

Mello, 1999). The steranes distribution of this formation is dominated by

C27 and C29 steranes (20SCR) (Figure 4C). This is held to be diagnostic of

nonmarine organic sources (Moldowan et al., 1985). However, the organic

matters were derived from marine carbonate source rocks older than Early

Cretaceous, generally showing high relative amounts of C29 steranes and at-

tributed to the algal precursors (Grantham and Wakefield, 1988; Peters and

Moldowan, 1993; Mello et al., 1995). All the above biological marker features

are characteristics of extracts derived from clay-rich source rock with more

contributions from terrestrial organic sources and limited input of marine

organic matter.


Table 1. Pyrolysis analyses of the studied formations in the onshore Nile Delta, Egypt

Well name Depth, m TOC, wt% S2 HI OI Tmax

Abu Madi Formation

Abu Madi-1 3740–3750 0.39–0.41 (2) 1.56–1.97 25–40 180–190 430–433

Qawasim-1 3760–3770 0.48–0.49 (2) 2.00–2.10 55–70 200–220 433–435

Abadiya-1 3760–3790 0.32–0.48 (2) 0.88–1.80 80–92 150–200 430–432

Kafer El Shiekh-1 3810 –3830 1.84–2.34 (2) 1.84–2.34 243–250 185–220 433–435

Sidi Salem Formation

Sidi Salem-1 4100–4160 0.69–1.45 (4) 3.88–5.42 198–220 98–130 434–436

Abadiya-1 4155–4175 0.88–0.96 (2) 4.69–4.78 356–421 150–160 436–440

Kafer El Shiekh-1 4200–4350 1.38–1.25 (4) 4.99–5.21 460–480 140–159 437–440

Abu Madi-1 4400–4500 1.67–1.70 (3) 5.00–5.21 480–500 90–130 440–444

Abu Madi-3 4550–4650 1.67–1.70 (3) 5.00–5.20 110–178 100–198 440–442

Moghra Formation

Abu Madi-5 4900–5200 1.11–1.67 (4) 5.00–5.20 300–402 80–102 438–444

Qawasim-1 4875–5100 1.42–1.82 (3) 5.10–5.22 325–350 50–70 440–445

Kafer El Shiekh-1 5150–5190 1.68–1.88 (3) 5.26–5.54 275–300 57–100 445–448

TOC: Total organic carbon (weight percent of the whole rock); S2: Residual petroleum potential (mg HC/g rock);

HI: Hydrogen index (mg HC/g TOC); OI: Oxygen index (mg CO2/g TOC); Tmax: Temperature at which maximum

emission of high temperature (S2) hydrocarbons occurs (ıC).

79

7


798 M. M. El Nady

Figure 3. Source rock evaluation of Abu Madi Formation, onshore Nile Delta, Egypt.

(A) TOC versus depth; (B) Rock Eval S2 versus depth; (C) HI versus OI; (D) Rock

Eval Tmax versus depth.

Sidi Salem Formation (Middle Miocene)

Fair-to-good source rocks predominant in the Middle Miocene (Sidi Salem

Formation, Figure 5A and 5B). This is indicated by TOC (wt%) and “S2” val-

ues (0.69 to 1.70 wt% and 3.88 to 5.21 mg HC/g rock, respectively, Table 1).



Figure 4. Representative gas chromatograms (A), ion fragmentograms (triterpanes

m/z 191, (B), and (steranes m/z 217, (C) of Abu Madi Formation in Kafer El Sheikh-

1 well (depth 3740–3750 m), onshore Nile Delta, Egypt.


800 M. M. El Nady

Figure 5. Source rock evaluation of Sidi Salem Formation, onshore Nile Delta, Egypt.





Also, HI values reveal that the source rocks of the Sidi Salem Formation

have generating capabilities of mixed oil and gas (II/III kerogen) as shown

from hydrogen index values (110 to 500 mg HC/g TOC (Table 1 and Fig-

ure 5C). The thermal maturation of this formation as indicated by Tmax (ıC)

(Table 1) indicates mature source rocks, where the majority of samples lie in

the oil zone (Figure 5D), except one sample from the Sidi Salem-1 well, are

marginally mature (Figure 4D) (Tmax less than 434ıC) (Table 1).

The gas chromatograms of the Sidi Salem Formation (Figure 6A) show

an even carbon preference of n-alkanes in the range n-C16 to n-C34. Low pris-

tane/phytane (pr/ph) ratios (0.71) suggest carbonate-rich source rocks for this

source rock, deposited under anoxic marine condition. Isoprenoids/n-alkane

(pr/n-C17 and ph/n-C18) ratios (0.52 and 0.66, respectively) (Figure 6A) re-

veal anoxic marine condition.

The ion fragmentograms (m/z 191 triterpanes) (Figure 6B) show a pre-

dominance of tricyclic terpanes and C28 bisnorhopanes suggesting source

rocks extract from marine algal and bacterial origin (Waples and Machi-

hara, 1991). Hunt (1996) recognized that the gammacerane is resistant to

biodegradation, it tends to be present in a variety of source rocks and oils but

its proportion is relative to other triterpanes which is particularly high in sam-

ples from hypersaline depositional settings (Huang, 2000). In the Sidi Salem

formation, the gammacerane concentration is relatively high (Figure 6B) sup-

port the interpretation of an anoxic and reducing hypersaline environment.

The homohopanes (Figure 6B) are slightly high , indicating marine carbonate

rocks (Huang, 2000).

The mass fragmentograms (m/z 217 steranes) show that the Sidi Salem

Formation is characterized by the dominance of C27 steranes (Figure 6C).

This is characteristic of significant marine organic matter contributions (Pe-

ters et al., 1994; Hunt, 1996). Also the dominance of C29 steranes patterns

(Figure 6C) suggests a higher plant contribution (Hunt, 1996). On the other

hand, Peters and Moldowan (1993) and Hunt (1996) reported that the ma-

rine carbonate in the source rocks have high C29 steranes, possibly because

of sterol precursor from marine brown and green algae or bacteria. There-

fore, the high relative amount of C29 steranes in the Sidi Salem Formation is

attributed to marine algal precursors. Also, the presence of C30 steranes (Fig-

ure 6C) indicates a marine depositional influence (Moldowan et al., 1985).

Moreover, the relatively low concentration of diasteranes compared to regular

steranes (Figure 6C) suggests a source rock with low clay content, consistent

with carbonate lithology (Huang, 2000). The low abundance of hopane (Fig-

ure 6B) relative to steranes (Figure 6C) indicates algal input (Abrams et al.,

1999).

Moghra Formation (Early Miocene)

The Moghra Formation has TOC values ranging from 1.11 to 1.88 wt% and

rock-Eval derived S2 from 5.00 to 5.54 mg HC/g rock (Table 1) indicating


802 M. M. El Nady

Figure 6. Representative gas chromatograms (A), ion fragmentograms (triterpanes

m/z 191,(B), and (steranes m/z 217, (C) of Sidi Salem Formation in Kafer El Sheikh-

1 well (depth 4200–4350 m), onshore Nile Delta, Egypt.



good source rocks (Figures 7A and 7B). In the plot of hydrogen index versus

oxygen index (Figure 7C), the samples of the Moghra Formation from wells

Abu Madi-5, Qawasim-3, and Kafer El Sheikh-1 are plotted in the mixed

type kerogen (II/III), where HI is ranging from 275 to 402 mg HC/g TOC

(Table 1). The Tmax (ıC) (Table 1) indicates mature source rocks, where

most samples of this formation lie in the oil zone (Figure 7D).

The Moghra Formation has higher pr/ph ratio (1:30). Also, isoprenoids

to n-alkane ratios (0.72 and 0.53, respectively, (Figure 8A) indicate an origin

from mixed Type II and III organic matters, deposited under suboxic condi-

tions. This formation has odd over even n-alkanes preferences in the ranges

n-C21, n-C27, and n-C29 (Figure 8A) which suggests mixed organic sources

(Hunt, 1996).

The Moghra Formation has slightly higher tricyclic terpanes (Figure 8B),

suggesting source rock that contains nonmarine and higher plant organic mat-

ter (Hanson et al., 2000). Also, the smooth decreasing in the homohopanes

(C31–C35) profile (Figure 8B) reflects a clastic facies (Waples and Machi-

hara, 1991). The low gammacerane concentration in the sample (Figure 8B)

indicates a low salinity level at the time of their source rock deposition. The

presence of oleanane (Figure 8B) indicates higher plant contribution and sug-

gests that the source rock is of tertiary or a younger age. The relative high

levels of diasteranes (Figure 8C) indicates a clay-rich source rock (Peters

et al., 1999), because a clay catalysis is required for the production of di-

asteranes during catagenesis (Peters et al., 1999). Additionally, the relative

high abundance of C27 and C29 steranes suggests that the source organic

matter was very rich in both terrigeneous and marine organic matter (Huang

and Meinschein, 1979).

Geochemistry of Condensates

Three condensate samples were taken from Abu Madi, Sidi Salem, and

Moghra formations in wells Abu Madi-1, 3, and 5, respectively (Figure 1).

The results of the organo-geochemical analyses are summarized in Table 2.

The gas chromatograms of the Abu Madi condensate from well Abu

Madi-1 (Figure 9A) shows moderate concentration of n-alkane with a high

pristane/phytane ratio (1:90) (Figure 9A) and isoprenoide/n-alkane ratios

(pr/n-C17 and ph/n-C18) are 0.83 and 0.46, respectively (Table 2), suggesting

terrestrial organic sources. For the condensates of Sidi Salem and Moghra

formations (Figures 9B and 9C, respectively) shows a high-to-moderate con-

centration of n-alkane with slightly even carbon preference in the range n-

C10 to n-C30. The high pristane/phytane ratio (1.97 and 3.33, respectively)

(Table 2) and isoprenoide/n-alkane ratios (pr/n-C17 and ph/n-C18) are 0.77,

0.38 and 0.91, 0.29, respectively (Table 2). These data suggest mixed organic

sources with terrestrial input (Peters and Moldowan, 1993) and suboxic to

oxic depositional conditions (Peters et al., 1994).


804 M. M. El Nady

Figure 7. Source rock evaluation of Moghra Formation, onshore Nile Delta, Egypt.





Figure 8. Representative gas chromatographs (A), ion fragmentograms (triterpanes

m/z 191, (B), and (steranes m/z 217, (C) of Moghra Formation in Qawasim-1 well

(depth 4875–5100 m), onshore Nile Delta, Egypt.


Table 2. GC and GC/MS of condensate samples from some wells, onshore Nile Delta, Egypt

Wells Depth, m Formation Pr/Ph Pr/n-C17 Ph/n-C18 Ts/Tm

Sterane

ratios

C35/C34

ratios

Abu Madi-1 3740–3750 Abu Madi 1.90 0.83 0.46 1.80 0.50 0.41

Abu Madi-3 4110–4180 Sidi Salem 1.97 0.77 0.38 2.33 0.55 0.60

Abu Madi-5 5150–5190 Moghra 3.33 0.91 0.29 1.80 0.60 0.94

Pr/Ph:Pristane/phytane ratio; Pr/n-C17: Pristane/C17 normal alkane; Ph/n-C18: Phytane/C18 normal alkane; Ts/Tm:trisnor-

hopanes/trisnorneohopanes ratios; Sterane ratios: %C29 20S/20SC20R; C35/C34 Homohopanes ratios.

80

6



Figure 9. Representative gas chromatograms of Miocene condensates, onshore Nile

Delta, Egypt.


808 M. M. El Nady

The mass fragmentograms (m/z 191) of condensates (Figure 10) show

that the concentration of tricyclic terpanes is slightly low for the Abu Madi

condensate (Figure 10A) than the condensates of the Sidi Salem and Moghra

formations (Figures 10B and 10C) suggesting low maturity of Abu Madi

condensate and/or low salinity of the depositional environment than the other

condensates (Huang, 2000). The C30 hopane is higher than the condensates

(Figure 10) and illustrate that the condensate samples were sourced from

source rock rich in carbonaceous organic matters. The presence of C30 ole-

neane in all condensates (Figure 10) which is derived from Late Cretaceous

and tertiary angiosperms (Murray et al., 1994), indicate terrestrial input (Ken-

nicutt et al., 1991). On the other hand, the presence of C29 normoretane,

C30 moretane, and slightly higher concentrations of C28, C29 bisnorhopanes

in the Abu Madi and Sidi Salem condensates (Figures 10A and 10B) sug-

gesting more of a contribution from terrestrial sources with an input from

marine origin (Riediger et al., 1990). The smooth decrease in the C31-C35

homohopanes profile (Figure 10), suggests a clastic rock facies (Waples and

Machihara, 1991). Sidi Salem condensate, characterized by C29 norhopane,

is approximately equal to C30 hopane (Figure 10B), suggesting that this con-

densate was generated from calcareous rocks (Connan et al., 1986). On the

other hand, the absence of gammacerane (Figures 10A and 10B) is interpreted

as molecular features, which suggest a terrestrial origin. The absence of C29

normoretane and C30 moretane in the Moghra condensate (Figure 10C) sug-

gests a contribution from marine organic matters with little input from the

terrestrial source (Hunt, 1996).

The ion fragmentograms (m/z 217, Figure 11) show that the relatively

high abundance of diasteranes in the Abu Madi condensate (Figure 11A)

rather than the Sidi Salem and Moghra condensates (Figures 11B and 11C)

indicate that the liquid petroleum originated from a clay-rich source rock (Pe-

ters et al., 1999). The predominance of C27 regular steranes (20S and 20R)

over C29 steranes (20S and 20R) of the Abu Madi and Moghra condensates

(Figures 11A and 11C) suggests a significant contribution from marine or-

ganic matters with little input from a terrestrial source. While in the case of

the Sidi Salem condensate (Figure 11B), the C29 steranes (20S and 20R) are

predominant over C27 steranes (20S and 20R) indicating more of a contribu-

tion from terrestrial organic matters (Huang and Meinschein, 1979).

Maturity of Condensates

The tricyclic terpanes, Ts/Tm, C35/C34 homohopanes and C29 20S/20SC20R

ratios were used as a qualitative indicator of maturity (Van Graas, 1990). The

tricyclic terpanes in the Abu Madi condensate (Figure 10A) seem to be in

low abundance than the other condensates (Figures 10B and 10C) and the

diasteranes (Figure 11A) is slightly higher than the others (Figures 11B and

11C). Furthermore, the Ts/Tm, C35/C34 homohopanes and C29 20S/20SC20R



Figure 10. Representative ion fragmentograms (triterpanes m/z 191) of Miocene con-

densates, onshore Nile Delta, Egypt.


810 M. M. El Nady

Figure 11. Representative ion fragmentograms (steranes m/z 217) of Miocene con-

densates, onshore Nile Delta, Egypt.



ratios are 1.80, 0.41, and 0.50, respectively. These parameters seem to be less

than those of the Sidi Salem and Moghra condensates (Table 2) indicating a

low thermal maturity of the Abu Madi condensate. Moreover, the condensates

of Sidi Salem and Moghra formations were generated from source rocks,

which are more mature than the Abu Madi condensate previously mentioned

(see Figures 3, 5, and 7), where the source rock of the Abu Madi Formation

is Type III kerogen (Figure 3C) and lies in the early stages of a hydrocarbon

generation (Figure 3D), while the condensates of the Sidi Salem and Moghra

formations were generated from mature source rocks of Type II/III kerogen

(Figures 5C and 7C) and lie within the oil zone (Figures 5D and 7D).

Thermal Geochemical Modeling

The geochemical thermal modeling of the Miocene source rocks of the studied

portion in the onshore Nile Delta was constructed for the drilled section

which includes the stratigraphic sequence and the timing of events in the

Nile Delta that are Triassic-Jurassic time, Late Cretaceous-Early Tertiary,

and Tertiary events. These tectonic events were incorporated in the models.

The geochemical gradient of 2ıC/100 m was employed based on the bottom

hole temperature (BHT) that was recorded during drilling after correction by

using the Horner method (Fertle and Wichman, 1977). The data was input

with Basin Mod software. Preliminary maturation modeling using Lopatin’s

method (1971) proved very useful in suggesting the source intervals and

timing of petroleum generation, expulsion, and migration. The purpose of

these models is to evaluate the maturity of potential source rocks and to

estimate their timing of maturation. There is a correlation found between

measured and calculated maturities of potential source beds calibrated against

the available measured maturity parameters, which included mainly vitrinite

reflectance data from Abu Madi-3 and Abu Madi-5 wells. In the present work,

the early stage of hydrocarbon generation is in between vitrinite reflectance

(Ro D 0:6 to 0.85%). The oil window is defined as the depth interval between

peak of hydrocarbon generation (Ro D 0:85%) and the gas generation (Ro D

1:35%), while the gas generation at Ro (1.35 to 2.6%) according to Waples

(1985).

In the Abu Madi-3 well, the geochemical burial model and maturity pro-

file (Figures 12A and 12B) indicates that Moghra and Sidi Salem formations

(E-M. Miocene) are in the mature stages of hydrocarbon generation (defined

by 0.85-1.35% Ro) at 4–6 million years before the present (mybp), while

the Qawasim and Abu Madi formations (L. Miocene) are in the early stages

of hydrocarbon generation (defined by 0.6–0.85% Ro) at 2–3 million years

before the present (mybp). In the Abu Madi-5 well (Figures 13A and 13B)

the Miocene source rocks lie in the mature stages of hydrocarbon (oil win-

dow, Ro D 0.85–1.35%) at 15–18 million years before the present (mybp).

Moghra and Sidi Salem formations are in the late stages of maturation (gas


812 M. M. El Nady

Figure 12. Geochemical model (A) and maturity profile (B) of sedimentary section

penetrated by Abu Madi-3 well, onshore Nile Delta, Egypt.


penetrated by Abu Madi-5 well, onshore Nile Delta, Egypt.



window, Ro D 1.35–2.60%) at 8–12 million years before the present (mybp).

In Kafer El Sheikh-1 well (Figures 14A and 14B) the Miocene source rocks

are in the early stages of hydrocarbon generation at 3–5 million years be-

fore the present (mybp). In the Sidi Salem-1 well (Figures 15A and 15B),

Mohgra and Sidi Salem formations are in the Middle stages of hydrocar-

bon generation (oil window) at 3–5 million years before the present (mybp),

while Abu Madi and Qawasim formations are in the early stages of matu-

ration (early generation) at 8–10 million years before the present (mybp).

This timing adds to the value of future explorations in the Nile Delta and

indicates that Miocene source rocks have expelled hydrocarbons during the

Pleistocene-Early Pliocene time.

As previously mentioned, the source rock of the Abu Madi formation

is Type III kerogen (Figure 3C) and lies in the early stage of hydrocarbon

generation until the present time (Figures 12 to 15), while the source rocks

of the Sidi Salem and Moghra formation were generated from mature source

rocks of Type II/III kerogen (Figures 5C and 7C) and lie within the oil

window until the present time (Figures 12 to 15). Moreover, the condensate

of the Abu Madi formation, as mentioned previusly, appears to be less mature

than the Sidi Salem and Mohgra condensates. This reflects that the studied

condensates have probably migrated from deep burial source rocks which

are at a higher level of maturity than from less mature source rocks in the

study area.


penetrated by Kafer El Sheikh-1 well, onshore Nile Delta, Egypt.


814 M. M. El Nady


penetrated by Sidi Salem-1 well, onshore Nile Delta, Egypt.

CONCLUSIONS

The Miocene source rocks as well as some condensate samples from Abu

Madi-1, 3, 5; Qawasim-1; Abadiya-1; and Kafer El Sheikh-1 wells in the

onshore Nile Delta were discussed through the advanced organo-geochemical

techniques as rock eval pyrolysis, gas chromatography, and gas chromatog-

raphy-mass spectrometric analyses. Also, four geochemical models of some

wells in the study area are discussed. The results are as follows:

1. The Late Miocene Abu Madi Formation, which originated from poor im-

mature to marginally mature source rocks and organic matter, has Type

III Kerogen deposited under terrestrial environment.

2. The Middle Miocene Sidi Salem Formation has fair-to-good mature source

rocks which have the capability of producing mixed oil and gas originating

mainly from marine organic matters.

3. The Early Miocene Moghra Formation has mature good source rocks for

kerogen (Type II/III) which originated from organic matter and was rich

in both terrigeneous and marine organic matter.

4. The geochemistry of condensates revealed that the Abu Madi and Moghra

condensates originated from marine organic matters with little input

from terrestrial sources. While Sidi Salem condensate was from terrestrial



organic matters, Abu Madi condensate was less mature than Sidi Salem

and Moghra condensates.

5. The geochemical thermal modeling of the Miocene source rocks indicates

that the Abu Madi formations are in the early stages of hydrocarbon until

the present time. Moghra and Sidi Salem formations are in the mature

stage of hydrocarbon generation until the present time. This indicates that

the studied condensates have probably migrated from deeply buried source

rocks which are at a higher level of maturity than from less mature source

rocks in the study area.

ACKNOWLEDGMENTS

The author is grateful to the authorities of the Egyptian General Petroleum

Corporation (EGPC) and the Belayim Petroleum Company for permitting the

publication of this work. Thanks are due to the StratoChem (New Madi) and

Egyptian Petroleum Research Institute (EPRI), Cairo, Egypt, for the different

organo-geochemical analyses. Thanks is due to Prof. Dr. Mahmoud Y. Zein

El Din, Geology Department, Al Azhar University, for critical reading and

reviewing this work.

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