Source rock evaluation and burial history modeling of Cretaceous rocks at the Khalda Concession of Abu Gharadig Basin, Western Desert, Egypt

https://doi.org/10.1016/j.jafrearsci.2021.104372Get rights and content

Highlights

  • Implications of 1D basin modeling in petroleum exploration and development.

  • TOC, Rock-Eval pyrolysis and %Ro data are used to assess the source rocks.

  • Entrapment styles of generated hydrocarbons are based on seismic data.

  • Abu Roash “F" Member has very good generation potential of oil-prone type.

  • Bahariya Formation has poor generation potential of gas-prone type.

Abstract

The Khalda Concession is located southeast of the Abu Gharadig Basin in the Western Egyptian Desert. The present study is based on Rock-Eval pyrolysis and vitrinite reflectance (%Ro) data of the SPYGLASS-1X and AG-24 wells and analyses of two-dimensional seismic sections. This study evaluates the hydrocarbon potential, quality of organic matter, and thermal maturation history of the Abu Roash F and G members and the Bahariya Formation in the two wells. In addition, two burial history models were constructed using the PetroMod software to determine the status of the studied sequences with respect to oil and gas windows and the timing of hydrocarbon generation, which depend on the modeled %Ro. The structural setting and entrapment styles of the generated hydrocarbons were detected via the interpretation of the two-dimensional seismic lines using the Petrel software platform. The results indicate that the hydrocarbon potentiality of the Bahariya Formation and the Abu Roash F and G members ranges from poor to very good with the total organic carbon reaching 2.5 wt%. The hydrogen index values indicate that the kerogen types are mainly Type II, mixed Type II/III, and Type III. In addition, the maturity parameters (%Ro, Tmax, and the production index) and the burial history models of the studied wells indicate that the Abu Roash F and G members and the Bahariya Formation have reached the mature stage at the studied depths. The seismic interpretation reveals that the entrapment styles of the generated hydrocarbons are primarily structural traps of normal faults, forming horst and graben structures, and anticline folds.

Introduction

In Egypt, the exploration and production of oil and gas began a long time ago and is ongoing at present with the discovery of the Zoher and Shrouk gas fields in the Mediterranean Sea. In the northern Western Desert of Egypt, exploration activities have led to the discovery of several oil and gas basins (e.g., Abu Gharadig, Gindi, Alamein, Beni Suef, and Matruh-Shushan) (EGPC, 1992; Abdel-Fattah et al., 2014, 2015; Abd-Allah et al., 2018). The study area (the Khalda Concession) is located northeast of the Abu Gharadig Basin in the north Western Desert (Fig. 1). Several hydrocarbon discoveries have been made in this highly faulted sedimentary basin. The Abu Gharadig Basin is considered to be one of the most prospective basins in the northern Western Desert of Egypt for oil and gas fields (El-Shaarawy et al., 1994) (Fig. 1). The Abu Gharadig Basin has been extensively studied by many groups (e.g., Abdel Aal and Moustafa, 1988; Bayoumi and Lotfy, 1989; EGPC, 1992; Hammad et al., 1992; Khaled, 1999; Nabawy and ElHariri, 2008; Moldowan, 2012; Teama and Nabawy, 2016; Abdel-Fattah et al., 2020). Schlumberger (1984) determined that the source rocks in the Abu Gharadig Basin are present within noncalcareous shale sequences that are associated with a transgressive event that occurred during the Late Jurassic and Cretaceous. The Abu Roash F member and the Bahariya Formation are thought to be the main oil source rocks in the Abu Gharadig Basin (Lüning et al., 2004; El Diasty and Moldowan, 2012; Abd-Allah et al., 2018).

The results from evaluations of the source rocks, including basin modeling, and seismic data interpretation reduce the risk of exploration and may lead to the discovery of new prospective areas. The source rocks were defined as sedimentary rocks having the ability to accumulate oil and/or gas. The hydrogen content of kerogen is thought to be the most important parameter controlling the generation of oil and gas (Maowen et al., 2006; Kamali and Mirshady, 2004).

The present study uses Rock-Eval pyrolysis and %Ro data for rock samples from the SPYGLASS-1X and AG-24 wells and two-dimensional (2D) seismic sections to evaluate the hydrocarbon potential, quality of kerogen, and thermal maturation history of the Cretaceous source rocks (the Abu Roash F and G members and the Bahariya Formation) in the Khalda Concession (Fig. 1). Two burial history models were constructed using the PetroMod software to determine the oil and gas window and the timing of the hydrocarbon generation using the modeled %Ro. In addition, the structural setting and the entrapment styles of the generated hydrocarbons were determined via an interpretation of 2D seismic lines using the Petrel software platform. Studying unconventional reservoirs has become the main object of exploration to increase crude oil reserves for many oil companies in Egypt, including Khalda and Apache. Accordingly, geochemical studies and basin modeling of the Abu Roash F and G members and the Bahariya Formation are a very important part of the future exploration of unconventional reservoirs in the Abu Gharadig Basin, especially the Abu Roash F member, which primarily consists of argillaceous limestone enrichment in organic matter with very low matrix permeability (Adly et al., 2016).

Section snippets

Lithostratigraphy

The lithostratigraphy of the Abu Gharadig Basin is composed of rock units ranging from the Precambrian to recent geologic time (Fig. 2) (EGPC, 1992). Its Paleozoic sediments vary from early Cambrian to Late Permian and un-conformably overlie a Precambrian basement and are in turn unconformably overlain with Jurassic sediments (the Eghei, Khatatba, and Masajid formations) and/or younger deposits (Fawzy and Dahi, 1992). During the Early Cretaceous, thick Neocomian–Albian marine sediments to

Tectonics and structures

The Abu Gharadig Basin is a part of the Egyptian Western Desert. This basin was affected by six major geotectonic cycles or phases, illustrated in Fig. 3, listed from younger to older as follows: the Red Sea phase (Oligocene–Miocene), Syrian Arc main phase (Paleogene), Sub Hercynian–Early Syrian Arc (Turonian–Santonian), Cimmerian/Tethyian (Triassic–Early Cretaceous), Variscan–Hercynian (Late Paleozoic), and Caledonian cycle (Cambrian–Devonian) (Meshref, 1990). The Western Desert is divided

Materials and methods

In this study, 36 cutting samples of the studied rock units from the SPYGLASS-1X and AG-24 wells (Table 2, Table 3, respectively) were analyzed for Rock-Eval pyrolysis and total organic carbon (TOC) by the StratoChem Services and EXLOG companies for the Khalda Petroleum Company. Subsequently, 12 ditch samples were selected and analyzed for %Ro based on the amount of TOC being equal to and/or greater than 0.5 wt% of the analyzed samples. These data were obtained from the Khalda Petroleum Company

Results and discussion

This study assessed the Abu Roash F and G members and the Bahariya Formation as the source rocks for produced hydrocarbons in the SPYGLASS-1X and AG-24 wells of the Khalda Concession at the Abu Gharadig Basin. The results of the TOC and Rock-Eval pyrolysis analyses of these formations are shown in Table 2, Table 3 Here, the hydrocarbon potentiality, types of kerogen, thermal maturation and generation, one-dimensional basin modeling, and the entrapment styles of the hydrocarbons are determined

Conclusions

The main conclusions of this study can be summarized as follows.

  • Based on the TOC and Rock-Eval pyrolysis results, the Abu Roash F and G members have very good hydrocarbon potentiality while the Bahariya Formation has poor to fair hydrocarbon potentiality.

  • The HI and QI values indicate that the kerogen is mainly Type II (Abu Roash F member) with a marine origin, mixed Type II/III (Abu Roash G member) with marine and terrestrial origins, and Type III (Bahariya Formation) with a terrestrial origin.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors submit deep thanks for the Egyptian General Petroleum Corporation (EGPC) for their permission to use these data to achieve this work. We are grateful to the Khalda Petroleum Company (KPC) for the materials of this paper. Profound thanks are extended to the StratoChem Services Company and EXLOG Company for analyzing the rock samples. Also, thanks are due to the Schlumberger Company for supplying us with the PetroMod and Petrel software used in this work. We thank Mr Brett Chamberlain

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