The “F” Member has a high organic content (regionally 1 to 5%) and is probably one of the main source rocks for the gas and oil in the Abu Gharadig Field.
Sandstone As A Resevoir rock 2012
Tanta University Faculty of Science Department of Geology Submitted byMohamed Mahmoud Ahmed El-shora Supervised by Prof. Dr. Hamza Khalil
Chapter I: IntroductionCHAPTER II: Reservoir characterization ofthe Gombe sandstone, southern Chadbasin NigeriaCHAPTER IV: Abu Gharadig Field AbuGharadig Basin, Egypt
is a clastic sedimentary rock composed mainly of sand-sized minerals or rock grains “quartz and/or feldspar” . A permeable subsurface rock that contains petroleum.Fragmental reservoir rocks.• SandstoneChemical and biochemical reservoir rocks.• Carbonate rocks “L.S – Dolomite”Miscellaneous reservoir rocks.• Include the Igneous and Metamorphic rocks
The two essential elements of reservoir rock : PorosityPermeability
• 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).
• Sediments are mainly continental, sparsely fossiliferous, poorly sorted, and medium- to coarse grained, feldspathic sandstones called the Bima Sandstone. Younger Chad formation Kerri-Kerri formation Gombe sandstone Gongila formation Older Bima sandstone
(Fig 2.2) Stratigraphic successions in the Nigerian sector of the Chad basin in relationto the Benue Trough (Obaje et al., 2006).
• coarse feldspathic and cross-bedded sandstones.• It has been dated Albian.• consists of sequence of sandstones, clays, shales and limestone layers.• Early Turonian age to the formation.• a sequence of sandstone, siltstone and shale.• The macrofauna is limited .Shell- BP palynologists dated the coal late Senonian - Maastrichtian.
• 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).• 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.
• 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).
• 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).
• 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).
• The sandstones are unconsolidated• Porosities are commonly in the range 20-30% (Fig. 3.9).• Permeability (<100 mD).
Figure 4.1 - Location of the Abu Gharadig Field and structural framework of the Abu Gharadig Basin,Western Desert (modified from Khaled, 1999).
• 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.
• 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).
• 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).
• 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.
• 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).
• 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).
• 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.