Condensate/Gas Ratio Variability and Prediction in the Obaiyed Field, Western Desert, Egypt: Integrated Technology for Effective Near-field Exploration

By

 Erdem Idiz¹, J. Westrich¹, P. van Laer¹, O. Podlaha¹, M. Nour-el-din², J. Schreurs², B. Bell³, P. Boerrigter³

(1) Shell International E&P B.V, 2280 AB Rijswijk, Netherlands (2) SENV, (3) Bapetco, Cairo, Egypt

 The development and application of reliable methods for predicting condensate-to-gas ratio (CGR) in the area of Obaiyed field in the western desert of Egypt, is a critical issue for both near-field exploration activities and ongoing redevelopment efforts within the field. As is commonly the case for gas/condensate assets, liquid production in Obaiyed has a significant impact on overall financial performance. CGR prediction is best approached from an integrated perspective that combines aspects of reservoir engineering, geochemistry, and petroleum systems analysis. The current study comprised the following elements: (a) a comprehensive evaluation of CGR variability based on PVT analyses and production test results (b) detailed investigation of condensate and gas geochemistry data aimed at establishing the underlying controls of CGR variability and (c) a 3-D basin modeling study to provide a regional understanding of source and migration factors impacting CGR. The results of the study showed:

- Gases and oil/condensates in the Obaiyed field and satellites are all from a common Khataba source, but multiple kitchen areas have contributed to the accumulations.

- The bulk of the ‘condensates’ are oils dissolved in the gases. Gases, in particular, show a large variation in maturity and vary systematically across the field. CGR values show a strong correlation with the gas maturities.

- Lateral and column height variations in all geochemical parameters dominate over stratigraphic variability at any one location.

- The CGR variability in Obaiyed is caused by incomplete mixing of several phases of charge that have entered the trap over time (i.e., oil, wet gas and dry gas). The gradients in fluid properties are likely due to (1) insufficient time for homogenization and/or (2) the presence of barriers/baffles in the Lower Safa Fm.

The key control on CGR in Obaiyed and surrounding prospects is whether there is charge access to highly mature dry gas coming out of the Matruh trough.