Understanding reservoir heterogeneity through water-saturation prediction via neural network — A case study from offshore Nile Delta

Abstract

In complex geologic settings with a great degree of heterogeneity in reservoir properties, such as submarine channel complexes as in the Nile Delta province, we face the challenge of characterizing the reservoir based on availability of different seismic attributes. Amplitude variation with offset (AVO) analysis and prestack inversion techniques show impressive results in delineating the gas-bearing reservoirs, especially in clastic systems. However, a shortage of available wells and/or seismic data leads to a challenge in applying AVO and any prestack seismic inversion approaches. In addition, quantitative prediction of water saturation (Sw) from seismic is ambiguous because of its independent nonlinear relationship with conventional seismic attributes and inversion products. Water-saturation prediction away from the well is essential in order to characterize the reservoirs effectively. Therefore, probabilistic neural network (PNN) analysis has been implemented to predict Sw 3D volume using full-stack seismic data and Sw logs. In this case study, we applied the proposed neural network workflow over one of the late-Pliocene gas-sandstone reservoirs, Sequoia Field, in the West Delta Deep Marine (WDDM) concession, offshore Nile Delta, Egypt. The resulting volume then was tested using two blind wells that haven't been used in the analysis. The predicted Sw volume contains fine details that were used with variance and spectral-decomposed volumes to understand the reservoir's internal architecture in terms of sand body geometries and connectivity. The resulting volumes were used to better define the reservoir and optimize a new development well location.

Application of Artificial Neural Network in seismic reservoir characterization: a case study from Offshore Nile Delta

“…Locations of the study wells and the blind well are shown. Modified from Mohamed et al (2017) wells and six development wells. The exploration wells are: Sapphire-2 and Rosetta-10, and the development wells are: Sequoia-D1 to -D6.…”

“…4). As presented by Mohamed et al (2017), the canyon is filled by many smaller channels that are stacked together to form the final shape of the reservoir (Fig. 3).…”

“…1) Samuel et al (2003). The field is located on the north-western margin of the outer slope of the Nile Delta, approximately 50 km from the nearest shoreline Mohamed et al (2017).…”

Extended Elastic Impedance Inversion for Better Delineation of Gasbearing Sand Reservoir, Saffron Gas Field, Offshore Nile Delta, Egypt

“…The area of interest includes Saffron field, which lies in the West Delta Deep Marine (WDDM) concession, 60-120 km offshore in the deepwater of the present-day Nile Delta [1] (Figure 1). Saffron field is a Pliocene submarine delta slope canyon system, with complex turbiditic channel-levee reservoirs [2].…”

Unlocking gas reserves in bypassed stratigraphic traps in a deepwater brownfield using prestack seismic inversion: A case study from offshore Nile Delta, Egypt

“…e trapping mechanism is stratigraphic along the eastern, western, and southern limits in the form of pinch-outs and dip closure in the north. Charging of the Pliocene reservoir in the WDDM concession is from the north, and the gas is a mixture of biogenic and thermogenic origin (Mohamed et al, 2017). e Scarab Field gas accumulation is likely controlled by the sealing character of the overlying mass-transport complex (MTC).…”