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Petroleum Potential of the Interpreted Paleozoic Geoseismic Sequences in the South Diyur Block, Western Desert of Egypt

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Petroleum Potential of the Interpreted Paleozoic Geoseismic Sequences in the South Diyur Block, Western Desert of Egypt GeoArabia, 2012, v. 17, no. 3, p. 133-176 Gulf PetroLink, Bahrain Petroleum potential of the interpreted Paleozoic geoseismic sequences in the South Diyur Block, Western Desert of Egypt Mohammed Y. Farooqui, Khamis Farhoud, Dia Mahmoud and Ahmed N. El-Barkooky ABSTRACT The South Diyur exploration block of nearly 38,000 sq km is located in the Farafra Oasis region in the Western Desert of Egypt. It is a frontier exploration area, the nearest well being Ammonite-1, a dry hole drilled by Conoco in 1979 immediately outside the southwestern corner of the block. The South Diyur Block is located on the probable northeast extension of the Kufra Basin in southeast Libya. Although prolific reserves of oil and gas occur in Paleozoic basins in North Africa and throughout the Middle East, to date, the targets for petroleum exploration in the northern Western Desert have been in Jurassic and Cretaceous rocks. The regional structural surface features in the South Diyur Block are the NE-trending Bahariya and Farafra anticlines interpreted as a deeply eroded and inverted Late Cretaceous structure on the southern extension of the Syrian Arc system. The oldest exposed rocks are a Cretaceous sequence of sublittoral sediments (the Campanian Wadi Hennis Formation) in the core of the anticline. The interpretation of the subsurface is based on 1,175 line-km of reprocessed 1970s-vintage 2-D seismic. Four sequence boundaries have been identified from the seismic data. SB-1 correlates with the Jurassic/Cretaceous boundary in Ammonite-1. SB-2 is regionally correlated with the Late Devonian to Early Carboniferous Hercynian unconformity that overlies deeply eroded and truncated Paleozoic sequences and possibly marks the regionally extensive Late Paleozoic basin inversion. SB-3 near the base of the interpreted Silurian sequence coincides with the ‘hot shale’ petroleum source rock that is present throughout North Africa and the Middle East. SB-4 is interpreted as a major unconformity at the top of an Upper Proterozoic sedimentary section that was misinterpreted as the Precambrian acoustic basement in Ammonite-1. Five seismic sequences relate to the seismic boundaries. SS-1, from the surface to SB-1 is characterized by subparallel seismic stratification and is composed mainly of sandstone with shale interbeds in Ammonite-1. SS-2, bounded by SB-1 and SB-2, is distinguished by parallel to subparallel seismic stratification. In Ammonite-1, the sequence of interbedded sandstone and shale is fresh-water bearing and lacking in top seals, thus reducing its prospectivity. The underlying SS-3 (SB-2 to SB-3) directly underlies the Hercynian unconformity and is characterized by semi-transparent seismic facies that may correspond to a thick Silurian shale sequence. SS-4 (SB-3 to SB-4) of probable Cambrian–Ordovician age has parallel seismic stratification. Deep channels are interpreted as evidence of a Late Ordovician–Early Silurian glacial phase that is present throughout North Africa and the Middle East. SS-5 (below SB-4) is marked by partial subparallel seismic stratification and block faulting. It probably belongs to the Late Proterozoic (Pan-African) phase of block faulting and pull-apart basins. Similar seismic geometries and facies occur in the Kufra Basin in southeast Libya and in many parts of the Arabian Plate, including the prolific petroleum systems of Oman. Exploration plays in the South Diyur Block are a combination of Paleozoic structural and stratigraphic traps associated with prospective fairways, and possible stratigraphic traps in the Late Ordovician–Early Silurian glacial channels. In addition, the interpreted Late Proterozoic sequences (SS-5) warrant further evaluation. In order to identify future exploration plays and drill targets, additional 2-D seismic (4,490 line-km), aeromagnetic and airborne gravity surveys will be integrated with the present seismic data and drilling results from Ammonite-1. This will allow a proper assessment of the magnetic basement, basin configuration and prospective fairways. 133 Downloaded from http://pubs.geoscienceworld.org/geoarabia/article-pdf/17/3/133/4568685/farooqui.pdf by guest on 27 September 2021 Farooqui et al. INTRODUCTION The South Diyur Exploration Block covers an area of 37,678 sq km in the Western Desert of Egypt (Figure 1a). Conoco (Continental Sahara Oil Company) explored the South Diyur and adjacent South Siwa and Dakhla blocks in the 1970s. The exploration program culminated in 1979 with the drilling of the Ammonite-1 and Foram-1 exploration wells, both of which intersected Tertiary, Mesozoic and Paleozoic strata and bottomed in commercial basement without identifying oil or gas shows. After nearly three decades without exploration activity, a consortium lead by India’s Gujarat State Petroleum Corporation Ltd (GSPC) is currently exploring the South Diyur Block. The South Diyur Block is centered on the Farafra Oasis at latitude 27.06°N and longitude 27.97°E, approximately 500 km southwest of Cairo and 300 km west of the River Nile at Asyut, and mid- way between the Dakhla and Bahariya oases. Figure 1b is a satellite image of the South Diyur Block overlain with the major geographic and cultural features. The Farafra depression is the second largest in Western Egypt after the Qattara Depression 300 km to the north-northwest. The Farafra Oasis is linked by road to Cairo via the railhead at Bawiti in the Bahariya Oasis to the northeast, and with Qena on the Nile through the Dakhla oasis and the railhead of El Kharga in the Great Oasis to the southeast. The Farafra Oasis is located within an irregularly shaped steep-sided triangular depression with its apex to the north. The northwestern and northeastern scarps have elevations of 275 m above sea level (a.s.l.). The floor of the depression (about 100 m a.s.l near Qasr El Farafra) rises gradually southward to the Dakhla escarpment. The El Quss Abu Said plateau on the northeastern edge of the depression, separated from the bounding escarpment by Wadi El Obeiyed, has a maximum elevation of 343 m a.s.l. Within the Farafra depression is the so-called White Desert located 45 km north of Qasr Farafra formed by the wind erosion of chalky deposits of the Upper Cretaceous Khoman Formation. The hot springs of Bi’r Sitta occur on the southeastern flank of El Quss Abu Said near Qasr El Farafra. Our study presents the interpretation of about 1,175 line-km of 1970-vintage reprocessed seismic data acquired by Conoco in the South Diyur Block. It is part of the minimum work commitments for the GSPC-led consortium, which includes the acquisition of aeromagnetic and gravity surveys over the entire block, approximately 4,490 line-km of new seismic data, and the drilling of four exploration wells. The interpretation of the data from 14 NW-trending and 6 NE-trending tie lines, reprocessed in Cairo on behalf of GSPC, identified four regionally mappable geoseismic reflectors which can be tied to Ammonite-1 that had a measured depth (MD) of 2,395 m (7,857 ft). The paper discusses the importance of these geoseismic reflections in understanding the geologic evolution, petroleum system and exploration potential of the South Diyur Block. The results are critical to the interpretation of recently acquired seismic data and in the planning of the proposed exploration wells. The combination of geoseismic data and the recently acquired aeromagnetic and gravity data should enable the identification of basinal areas having petroleum potential within the South Diyur exploration block. One of the prime targets of the present study is to predict a suitable stratigraphic column from surface to basement together with expected thicknesses as an aid to exploration, and to forecast the commercial total drillable depth in the basinal area for a projected combination stratigraphic well. REGIONAL GEOLOGY Proterozoic In Egypt, Proterozoic metamorphic and igneous rocks of the African Craton are exposed in the Red Sea Hills bordering the Gulf of Suez, in the southwestern corner of Egypt at Gebel Uweinat on the border with Libya and Sudan. In southern Libya they occur on the border with Chad in the Tibesti- Ghiarabub Mountains and in the Mourizidie area south of Gebel Bin Ghanimah near the Libyan border with Chad and Niger. 134 134 Downloaded from http://pubs.geoscienceworld.org/geoarabia/article-pdf/17/3/133/4568685/farooqui.pdf by guest on 27 September 2021 South Diyur Block, Western Desert of Egypt a 25°E 26° 27° 28° 29° 30° 31° 32° 33° 34° 35° 36° City Well SYRIA 33°N Mediterranean Sea Oil field N 0 200 Gas field 32° km 32° Mersa Matruh Sallum Alexandria Nile 31° Delta Port 31° Said Suez Canal JORDAN 30° Cairo 30° Sinai Western Desert 29° Gulf of Suez Gulf of 29° Aqaba Bahariya-1 SAUDI Ras Gharib A El Desouqy-1 ARABIA 28° 28° LIBY Foram-1 South R. Nile 27° Siwa South Diyur 27° Block Block Port Safaga LIBYA Ammonite-1 26° EGYPT 26° Dakhla Block Red Sea 25° 25° Ras Banas Peninsula 24° Aswan 24° 25° 26° 27° 28° 29° 30° 31° 32° 33° 34° 35° 36° b 27ºE 27º30' 28º 28º30' 29º N 0 50 Naqb El Seliem km di Hennis 27º30'N Wa 27º30' Ain El Maqfi Qur Hamra Ain Dalla i El Obeiyid d Gebel Gunna (N) Bir Murr Wa Farafra Oasis Bir Karawein d 27º 27º El Quss Abu Sai Gebel Gunna (S) Bir Dikka Qur El Izza 27º 27º30' 28º 28º30' 26º30' Figure 1: (a) Location of the South Diyur Block in the Western Desert of Egypt showing oil and gas fields and selected exploration wells. (b) Landsat image of the South Diyur Block overlain with major geographic and cultural features. 135 135 Downloaded from http://pubs.geoscienceworld.org/geoarabia/article-pdf/17/3/133/4568685/farooqui.pdf by guest on 27 September 2021 Farooqui et al.
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