Characterization of the Reservoir Potential of Yabus Formation in Melut Basin, South Sudan, Using Rock Physics Templates and Inversion of 3-D seismic data.

Abstract

3-D seismic and well data of the Gumry Oil Field were integrated to execute this study using petrophysical analysis, rock physics templates, and post-stack seismic inversion to characterize the reservoir potential of the Yabus Formation. The characterization involved lithology determination, quantifying effective porosity, and evaluating fluid saturation of the Yabus Formation. The density-thermal neutron cross plot was used in lithology determination, and the Yabus Formation was accurately differentiated into mainly sand, shaly sand, and shale units. The results from the gamma and density-neutron combined method indicate that the shale content in the Yabus reservoir is low, with an average shale value of approximately 20.15%. In Quanti.Elan technique: bound water, moved water, oil saturation, and matrix components such as illite and quartz were achieved. The rock physics template results, based on the Vp/Vs ratio cross plot versus P-impedance, also differentiated the lithology of the Yabus Formation into sands, shaly sands, and shale, respectively. The study also employed post-stack model-based seismic inversion to ascertain the lithology of the Yabus Formation. The findings indicate that the formation consists of sand and shale with lateral and vertical variations.

The effective porosity (PHIE) obtained from petrophysical findings has estimated values ranging from 11.6% to 20.8% throughout the reservoirs of the Yabus Formation. Rock Physics Templates results reveal that the effective porosity ranges from 5% to 28%, with an average value of about 15%. The Indonesian equation provided water saturation values ranging from 4.6% to 32.4%, with an average oil saturation in the net pay zone of about 72.4%. The results of the RPT cross plots show that the fluid types present in the Yabus Formation are oil and water. According to the findings of this study, which are based on the petrophysical and rock physics templates, the problem of high-water cut may be related to the reservoir issue of the Yabus Formation. This results in higher water production, which significantly decreases the overall recovery of oil, a finding that has profound implications for the oil production strategy in the area.