Reservoir characterization and modeling of fractured basement in ruman oil field, Melut Basin, South Sudan

Abstract

This research investigates the hydrocarbon reservoir potential of fractured basement rocks in the Ruman Field, located in the Melut Basin of South Sudan. An integrated approach, utilizing a combination of resistivity images, acoustic logs, lithological data, and seismic attributes, was employed to effectively evaluate the formation. The study identifies two primary sets of fractures from well data interpretation with a notable concentration around the Ruman A1 well, attributed to nearby faulting. However, the study of seismic attributes has shown significant fracture network at the uplift basement section. Fracture orientations predominantly trend NE-SW and NW-SE, with aperture widths ranging from 0.4 mm to 2.1 mm and mean hydraulic apertures between 0.7 mm and 2.7 mm. These findings indicate favorable conditions for hydrocarbon accumulation within the granitic gneiss lithology (Chandrasekhar, P.H., Mane, P., Rajappan, P., ONGC, WOB, Mumbai, 2015).

Cumulative intensity logs were analyzed to define mechanical zones, revealing three structural trends that correlate with the identified fracture systems. Variance and ant track seismic attributes further enhanced the understanding of fracture features in this extensional setting (Varsha, Malviya, Sanjoy, & Deelip, 2023). A comprehensive Discrete Fracture Network (DFN) model was generated, depicting ellipsoidal fractures with maximum lengths of 500 cm and widths up to 3 cm. The model indicates porosity and permeability distributions of 0.7% to 1.5% and 0.4 md to 2.1 md, respectively, with significant oil-bearing fractures trending NW-SW

The results underscore the importance of thorough fracture characterization for effective reservoir management and highlight the need for further studies, including well testing, geomechanical modeling and advanced 3D seismic imaging, to improve geological understanding and reduce exploration risks. By integrating techniques, this research aims to enhance predictions of reservoir behavior under various development scenarios, contributing to more effective hydrocarbon appraisal and development strategies.