Tanta University Faculty of Science

Department of Geology

SANDSTONE AS A RESERVOIR ROCK

Submitted by

Mohamed Mahmoud Ahmed El-shora

Supervised by

Prof. Dr. Hamza Khalil

Chapter I: Introduction

CHAPTER III: El Morgan Field Gulf of Suez, Egypt

CHAPTER IV: Abu Gharadig Field Abu Gharadig Basin, Egypt

CHAPTER II: Reservoir characterization of the Gombe sandstone, southern Chad basin Nigeria

Chapter I: Introduction • Sandstone is a clastic sedimentary rock composed mainly of sand-sized minerals or rock

grains “quartz and/or feldspar” .• Reservoir rock: A permeable subsurface rock that contains petroleum.• Reservoir rocks can be divided into three types:

• Sandstone

Fragmental reservoir rocks.

• Carbonate rocks “L.S – Dolomite”

Chemical and biochemical reservoir rocks.

• Include the Igneous and Metamorphic rocks

Miscellaneous reservoir rocks.

The two essential elements of reservoir rock :

Porosity

Permeability

Relationship Between Porosity & Permeability • Proportional relationship

Relationship Between Porosity & Depth • Inverse relationship

Depth

Porosity

Why sandstone is excellent reservoir rock?• have a primary porosity. • Well-sorted sands with nearly spherical grains.• variation in size and shape of the grains.

CHAPTER II:Reservoir characterization of the Gombe sandstone, southern Chad basin Nigeria

• The study area is located within longitude 11° 45` E and 14° 45`E and latitude 9° 30`N and 13° 40`N.

(Fig 2.1) Geologic map of Nigeria showing the inland basins and the Nigerian sector of Chad basin (Obaje et al., 2006).

2.1 GEOLOGY OF CHAD BASIN

• Sediments are mainly continental, sparsely fossiliferous, poorly sorted, and medium- to coarse grained, feldspathic sandstones called the Bima Sandstone.

OlderBima sandstone

Gongila formation

Gombe sandstone

Kerri-Kerri formation

YoungerChad formation

(Fig 2.2) Stratigraphic successions in the Nigerian sector of the Chad basin in relation to the Benue Trough (Obaje et al., 2006).

•2.2 Bima sandstone• coarse feldspathic and cross-bedded sandstones. • It has been dated Albian.

•2.3 Gongila formation• consists of sequence of sandstones, clays, shales and limestone

layers. • Early Turonian age to the formation.

•2.4 Gombe sandstone• a sequence of sandstone, siltstone and shale. • The macrofauna is limited .Shell- BP palynologists dated the coal

late Senonian - Maastrichtian.

•2.5 Kerri-Kerri formation• consists of loosely cemented, coarse to fine-grained sandstone

(cross bedded), massive claystone and siltstone; bands of ironstone and conglomerate occur locally.

• The coal in the formation has yielded palynomorphs on the basis of which Shell-BP palynologists dated it Paleocene and later by Adegoke et al. (1986).

•2.6 Chad formation• a succession of yellow and grey clay, fine- to coarse-grained sand

with intercalations of sandy clay and diatomites.• its age is range from Pliocene to Pleistocene.

CHAPTER III: El Morgan Field Gulf of Suez, Egypt• The El Morgan Field is

located in the southern sector of the Gulf of Suez

(Fig 3.1) - Location of the El Morgan Field (Alsharhan and Salah, 1995).

3.1 Stratigraphy and Depositional Facies

• The El Morgan Field reservoirs are Lower to Middle Miocene in age. • 90% of production occurs in the Middle Miocene Kareem

Formation; minor production comes from the overlying Belayim Formation; and minor reserves are contained within the Lower Miocene Nukhul Formation (LaChance and Winston, 1987).

The Kareem Formation

• consisting of medium to coarse-grained, arkoses and subarkoses, interbedded with dolomitic/ anhydritic mudrocks. • The Kareem reservoir is

divided into nine reservoir zones (Fig. 3.5; Zones A to I from top to bottom) which can be correlated across the entire field (Bentley and Biller, 1990).

(Fig 3.5) - Reservoir zonation of the El Morgan Field and typical wireline log response (Bentley and Biller, 1990).

3.2 Reservoir Properties

• The sandstones are unconsolidated• Porosities are commonly in the range 20-30% (Fig. 3.9).• Permeability (<100 mD).

CHAPTER IV: Abu Gharadig Field Abu Gharadig Basin, Egypt

Figure 4.1 - Location of the Abu Gharadig Field and structural framework of the Abu Gharadig Basin, Western Desert (modified from Khaled, 1999).

4.1 Stratigraphy and Depositional Facies

• Kharita Formation is a series of sandstone bodies contain gas in some wells of the Abu Gharadig Field .• The Kharita Formation is followed by the shallow marine to

coastal shales and fluvio-deltaic sandstones of the Cenomanian Bahariya Formation, which is very sand-rich in the south and southeast of the Abu Gharadig Basin.

Bahariya Formation• The Bahariya Formation has been subdivided into three informal units in

the Abu Gharadig Field, labeled “Upper Bahariya”, “Middle Bahariya”, and “Lower Bahariya” (Kenawy, 1988) (Table 4.1).

Abu Roash Formation • characterised by a cyclic alternation of deltaic flood-plain

sandstones, coastal sandstones and shales, and shallow marine shales and limestones.

• Abu Roash Formation “G” Member, is Cenomanian in age, and is mainly composed of marine shale with thin carbonates and sandstones.

• Member “F” (Late Cenomanian) is composed of massive bedded, dolomitic, shelly wackestone, with laminated bituminous wackestone and microbioclastic mudstone (Fig. 4.3).

• The Abu Roash “E” Member is Late Cenomanian to Turonian in age and is composed of shale, limestone and sandstone, deposited in a shallow marine environment.

• The shales at the base of the member are organic-rich and are considered to be one of the source rocks for the oil in the field (Khaled, 1999).

Figure 4.3 - Interpreted Sonic Log of typical Abu Roash “D”, “E” and “F” Members (Bayoumi, 1996).

• The shallow marine carbonates of the Turonian Abu Roash “D” Member (Fig. 4.3) contain minor reserves of oil in the Abu Gharadig Field (Table 4.2). They are overlain by the sands and shales of the Abu Roash “C” Member (Fig. 4.5), which comprises two regressive cycles separated by a regional coal bed marker (Wasfi et al., 1986). It is subdivided into four informal units, labeled 1 to 4

Figure 4.5 - Type lithological section of the Abu Roash “C” Member in well Abu Gharadig-25 showing the breakdown into four lithogenetic units and their environmental interpretation (Wasfi et al., 1986).

4.3 Reservoir Architecture

• The principal oil-bearing reservoirs in the Abu Gharadig Field are the sandstones of the Abu Roash “C” and “E” Members.

• The best reservoirs in the Bahariya Formation occur in the Lower and Middle Bahariya Members.

4.4 Reservoir Properties

• A) The Unit 2 sandstones of The Abu Roash “C” Member are fine-grained, slightly feldspathic and micaceous quartz arenites, with quite a high percentage of heavy minerals, which gives anomalously high gamma-ray and density logs (Wasfi et al., 1986).

• Average porosity 21%• permeability ranging from 130 to 150 mD (Table 4.1).

4.4 Reservoir Properties

• B) Abu Roash “E” Member, which has a reported average porosity of 16% and an average permeability of 40 to 500 mD (EGPC, 1992) (Table 4.1).

• C) The Abu Roash “D” Member is a minor 26 ft carbonate reservoir in the Abu Gharadig Field, which is only productive in two wells (AG-5 and AG-22).

4.4 Reservoir Properties

• A) Upper Bahariya Member have low porosity and permeability, and are not classed as good reservoirs

• B) The Middle and Lower Bahariya sandstones are better, thicker, and more extensive reservoirs, and represent 23% of the total thickness.

• Average porosity ranges between 2 and 19% (Kenawy, 1988)• Permeability is relatively low, with an average of 8-10 mD

and a maximum of 58 mD.

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