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Our Nile Delta example is from the South El Manzala field, it is based on the published dataset of Wazery et. al. (2011)*. The South El Manzala field is a gas field on the shore of the Nile Delta. Target reservoir we have applied the new saturation model to is in the Wastani formation. An upper Pliocene age siliciclastic deposit described as being of fluvial and offshore marine origin.
The shallow shaly sand gas reservoir of the Wastani formation we have evaluated should really not be described as a low resistivity low contrast reservoir. It is a reservoir with no discernible contrast in resistivity. The authors encountered challenges in precisely determining water saturation and consequently struggled to determine the pay intervals, despite employing saturation models designed for shaly sand formations. They had to use the lower velocity ratio associated with gas reservoirs to qualitatively identify the pay intervals
Our proprietary algorithm (Omovie, 2024) was applied to the measured compressional and shear sonic log data to estimate water saturation (Swt). The Swt from the new model is shown in the well log plot below, it is the red curve labeled SwT_VpVs. The average Swt estimate from the new saturation model for both intervals with pay flags (Swt>70%) is 59%. In comparison, the shaly saturation model used by the authors in the paper indicated that Zone B has an average Swt of 80% with only a combined pay zone of 2m all within Zone A. Both intervals were perforated and tested. Zone A tested 7.65 MMSCF/D while the lower pay interval – Zone B – tested 2.5 MMSCF/D of gas.
The new model was able to identify and quantify pay across intervals that were missed by resistivity-based shaly sand saturation models.
The new petrophysical interpretation is consistent with production test data from both intervals
For further details on our methodologies, technologies, and the outcomes of this case study, please contact us.
*Wazery, M., Bellah, H., & Abdel, S., 2011, Using Dipole Sonic Data for Low Resistivity Pay Detection at Shaly Sand Reservoir in the Nile Delta Gas Field 10th Offshore Mediterranean Conference and Exhibition Ravenna, Italy.
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