Pre-Messinian Tight Reservoir Characterization — Western Nile Delta, Egypt
The West Delta Deep Marine concession located approximately 100 km offshore of Alexandria, Egypt is of clastic nature with a variety of tectonic styles. Delineating reservoir presence and its effectiveness at the pre-Messinian level become the major geological risk, in addition to it being geophysically challenging due to the presence of multiple high contrast lithology at the shallower interval. Historically, bright spots which might be associated with the presence of hydrocarbon potential reservoirs may easily be detected at the Pliocene level (Vaughan et al, 2014). However, it is proven that highly cemented sands by carbonates or quartz over growth are widely distributed along with the presence of tight stringers, sand-shale overpressure and/or the effect of anisotropy which could also bring false information in the deeper section (Dolson et al, 2014). Early to Late Miocene is known as non-favorable for DHI, therefore quantitative interpretation over these intervals at the West Delta Deep Marine is challenging. Regional rock sensitivity analysis based on wells has been produced to understand the acoustic-elastic response within this area and subsequently tied to the seismic data. It is crucial to understand both the rock compaction trend and the seismic data in order to detect energy changes which may display different polarity for the reservoir as well as the hydrocarbon case. Seismic modelling in 1D and 2D scales from different regional wells at the same interval enabled the interpreter to capture uncertainty in thickness, tuning and variation in reservoir effectiveness. Anisotropy as another factor was also considered in the model. Detailed seismic data analysis and conditioning were carefully carried out for offset/angle stacks in particular, and this has become a critical part of a QI workflow prior to any geomorphological reconnaissance and AVO/AVA analysis in areas of interest. Amplitude and frequency of the seismic in some areas were lost due to the Messinian evaporite and gas chimneys. Interaction between individual offset/angle stacks to capture the correct response of the rock was carefully observed in the well log and the seismic scale. Dip structural noise removal, amplitude correction and alignment of seismic offset/angle gather calibrated to the rock physics model were performed to increase reliability of the data and thus the accuracy of the reservoir prediction from seismic. This workflow has resulted in the attenuation of noise while preserving the signal, and ultimately an optimized seismic data.
This iterative and integrated process has resulted in an optimized approach that is suitable for reservoir and hydrocarbon determination through quantitative interpretation. Successful application of this workflow in the lead and prospect maturation campaign could open up more opportunities and increase chance of success to explore this deep pre-Messinian play.
AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019