Prospect Revalidation Using Integrated Perspective Leads to No-Drill Decision

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 228825, “A No-Drill Decision for Beige Deepwater Prospect: An Integrated Subsurface Perspective,” by Obinna Chudi, SPE, Renaissance Africa Energy, and Kumar Gautam and Chima Chikezie, Shell, et al. The paper has not been peer-reviewed. _ The Beige prospect in deepwater offshore Gulf of Guinea represents a major exploration opportunity. Following the outcome of a neighboring well that drilled into an anomaly which turned out wet, Beige maturation was deferred for revalidation. The results confirm that the Beige deepwater opportunity is valid. However, in comparison with previous evaluations, an approximately 43% reduction in recoverable volume was observed. The recommendation from the subsurface team enabled an on-time business decision to suspend the Beige exploration well from the drilling sequence until an optimally commercial development approach is realized. Geological Setting The study area is in a mid- to lower-slope deepwater setting offshore the Gulf of Guinea along west Africa’s passive margin. A series of canyons developed during the Tertiary that incised into the shelf margin and extended basinward. Canyons formed major point-sourced conduits for sedimentation in the deepwater environment. The principal mode of downslope transport was by turbidity currents and associated mass-transport processes leading to the deposition of sand-rich turbidites. These form the principal reservoirs and plays for active hydrocarbon exploration and production today. A marine sedimentary unit, the Akata Formation, underlies the entire stratigraphic sequence. The marine mud crops out offshore in the form of mud diapirs resulting from smectite. These mud diapirs are partly responsible for modifying the slope system, leading to the development of both structural and stratigraphic traps, particularly within the study area. The Akata is thought to be the primary source rock in the Niger Delta petroleum province. Data and Methodology The 3D seismic data used in this study is broadband seismic recently acquired using streamer technology with a cable length of 10,050 m (Fig. 1). This data was acquired after the drilling of the nearby Bassa-X exploration well in 2022 to enable an improved understanding of the subsurface across the study area. The seismic showcases the structure and stratigraphy within a 6-second two-way time window. The frequency of this survey entailed preserving both the useful low frequency and noise-free high frequency. The velocity model-building approach was full waveform inversion. In addition, an anisotropic velocity model was added as a second pass. The velocity product in the end was properly constrained by geological boundaries. The data was processed using the Kirchhoff PreSDM algorithm. The processing algorithm deployed in the latest seismic resulted in a broadband frequency content with high resolution, good signal/noise ratio, improved structural imaging, better amplitude balancing, and seismic-loop continuity. The data is zero-phase seismic with a negative polarity displayed as a trough that represents an increase in acoustic impedance. Reliable technologies were deployed in the subsurface evaluation, leading to an improved understanding of the Beige prospect. Artificial intelligence-backed applications were used to generate fault-probability cubes using full-stack conditioned relative acoustic impedance cube and wide-band spectral decomposition volumes. Much of the complete paper is devoted to a discussion of the Bassa project, which resulted in a wet well.