Lower Safa Sedimentological Study, New Insights in the Reservoir Quality Distribution of the Obaiyed field, Western Desert, Egypt
- Ahmed Saad Abd El Badea (BADR Petroleum Co.) | Michiel C. De Groot (Shell P&T) | Xavier Le Varlet (Petroleum Development Oman)
- Document ID
- Society of Petroleum Engineers
- North Africa Technical Conference and Exhibition, 14-17 February, Cairo, Egypt
- Publication Date
- Document Type
- Conference Paper
- 2010. Society of Petroleum Engineers
- 1.6 Drilling Operations, 5.5.8 History Matching, 4.1.5 Processing Equipment, 5.2.1 Phase Behavior and PVT Measurements, 5.1.3 Sedimentology, 5.1.2 Faults and Fracture Characterisation, 1.2.3 Rock properties, 4.6 Natural Gas, 5.1.1 Exploration, Development, Structural Geology, 2.4.3 Sand/Solids Control, 5.5.2 Construction of Static Models, 1.1 Well Planning, 4.1.2 Separation and Treating, 5.5.3 Scaling Methods, 5.1.5 Geologic Modeling, 5.1 Reservoir Characterisation, 1.6.9 Coring, Fishing
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The Obaiyed gas/condensate field is located the Western Desert 50Km South of Marsa Matrouh. The Jurassic Lower Safa member (the reservoir bearing unit) consists of massive sandstones, which after deposition were subject to extensive deformation. A wide range of reservoir qualities is found in the field, with permeabilities ranging from tight (sub 0.1 mD) to high (up to 600 mD). Even after drilling 11exploration/appraisal and 30 development wells in the Obaiyed area, there are still significant subsurface uncertainties in the reservoir quality and extension, as shown by the 20% failure rate of the development wells. In order to improve our understanding of the Lower Safa reservoir, EREX Egypt was asked to make core descriptions for 15 wells in the Obaiyed field. They described 824m out of 1300 m total core length, to determine the depositional model of the Lower Safa. The conclusion of the study was that the main reservoir can be described as an estuarine deposit, with strong tidal influences in the earlier sequences, that evolved vertically into a wave-dominated deposit. The sedimentological study resulted in a simplified facies scheme that was used in Petrel to generate a 3D model for history matching. Unfortunately, it proved impossible to make a core-log correlation that could guarantee the successful production of new development wells. It was decided to take the reservoir quality uncertainty as a given and develop a completion strategy that would enable BAPETCO to produce the wells in any case. Therefore BAPETCO is planning a staged massive frac strategy in the coming years in parallel to the infill drilling campaign to maintain our production plateau and increase the ultimate recovery from the field.
Obaiyed Gas-Condensate field, one of the biggest onshore fields in Egypt, includes most challenges you could find in the world in a single place: facies changes, reservoir thickness variation due to erosion, diagenesis, two stages of HC fill and structural complexity. This paper describes the field history, reservoir characterization and its impact on the reservoir performance, the results of the sedimentological study which was carried out and further plans to develop and unlock the tight areas in the field using the massive frac strategy.
Brief subsurface description of the field
The Obaiyed field is located in the western desert of Egypt, some 50 Km south of the Mediterranean coast (see figure 1). The sandstone reservoir is of Jurassic Lower Safa age, the trap consists of a 4-way dip closure (see figure 2). Large reservoir quality differences characterize the field, posing special challenges to development. The Lower Safa is subdivided into an upper (units 1-3) and a lower accumulation (unit 5), separated by the non-reservoir unit 4. An erosional surface, known as waste zone and which is locally preserved as Siltstone, Conglomerates and Palaeosols, overlays the top of Lower Safa.
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