The Nile Delta deep water is rapidly emerging as a major gas province. A number of multi-TCF gas fields have been discovered in the deep water of the Nile Delta in the last few years. Offshore discoveries were made on the Pliocene deep marine turbidities reservoirs of the Rosetta and WDDM Fields. All of the exploratory wells were drilled targeting Plio-Pleistocene levels based on seismic amplitude anomalies, which showed many features indicative of the presence of gas. Only two wells were drilled into deeper targets (Oligocene-Miocene) but failed. The potential of the PreSalt Play is enormous but the risks are high at present, it is considered less attractive than shallower options.
Recent advances in deepwater drilling technology, coupled with the use of 3D seismic attributes, AVO analysis, and prestack inversion, have highlighted the encouraging prospectivity of the Oligo-Miocene sequences. The spectral decomposition played a significant role in the deep channels detection. However, the differentiation of gas sand and brine sand still the main challenge. The deterministic "blocky" AVO modeling for the wet wells shows that both gas and brine sands follow class I, and in extreme cases class Ilp.
In this paper, we applied stochastic rock physics modeling in which we made perturbations for gas saturation, porosity, and volume of clay stochastically to measure all Intercept/Gradient possibilities. The stochastic modeling indicates that the gas presence increases the gradient, structural clay has a minor effect, and the dispersed clay increase pushes toward the background trend. Although the clouds of both brine sand (in-situ case) and gas sand (substituted case) are partially overlapped, we still have the chance to separate them. Using a rotation angle of 17°, with a proper scalar, the intercept and gradient volumes were projected in an extended elastic reflectivity (EER) form to represent a fluid stack volume. The distribution of the gas and brine sands' clouds were then used to determine the probability of each point inside the fluid volume. After being tested at the wells locations, the final gas probability and brine probability volumes were used to de-risk the deep targets and explore for more.
