An Integrated Geophysical Approach for Prospect Maturation and De-Risking. The Sahara Upstream Production Nigeria Limited (Supnl) OPL 228 Case Study

Abstract

This paper presents a comprehensive integrated geophysical workflow implemented on Sahara Upstream Production Nigeria Limited's (SUPNL) Oil Prospecting Licence 228 (OPL 228), an onshore exploration block straddling the Niger Delta and Anambra sedimentary basins in Nigeria. The study demonstrates how systematic integration of 3D seismic acquisition, advanced processing, and detailed interpretation significantly used to delineate several exploration opportunities, prospect maturation, de-risking and exploration opportunity ranking, economic analysis for final investment decision and optimizing asset development strategy in complex fault-bounded plays within frontier exploration settings. The exploration workflow commenced with legacy 2D seismic data analysis, which identified six initial leads classified into high-grade and lower-grade leads. Subsequently, approximately 350 km2 of long-offset, long-record-time (LO-LRT) 3D seismic data were acquired and processed using state-of-the-art technologies to enable high-resolution subsurface imaging. The 3D seismic re-evaluation revealed substantial improvements over 2D structural interpretations, including spatial repositioning of prospects, modified fault-to-prospect relationships, resolution of complex structural geometries previously unresolved by legacy data and helped in progressing and developing the identified leads to prospects. Detailed prospect characterization incorporated fault seal analysis using Shale Gouge Ratio (SGR) methodology, attribute and AVO analysis, amplitude conformance studies, and probabilistic volumetric assessments under multiple geological scenarios to quantify resource potential and associated uncertainties, economic analysis was conducted leading to investment decision and development strategy for the asset. The integrated methodology resulted in the maturation of three opportunities with un-risked and risked prospecting resource volume of 150 and 70 million barrels of oil equivalent (MMboe) respectively and identification of additional leads with 700–800 million barrels of oil equivalent un-risked potential. Critically refined structural interpretation and prospect evaluation enabled optimization of the exploration well surface location and wellsite which was relocated from the initial western part of the block to the eastern location resulting in reduction of the required access road length from 5.2 km to 3.1 km. This optimization generated substantial cost savings, minimized environmental footprint, and accelerated project delivery timelines. Beyond resource identification, the geophysical program significantly enhanced understanding of the structural architecture and sequence stratigraphic framework within the transitional zone between the Niger Delta and Anambra Basin, providing insights applicable to regional exploration strategies and contributing to Nigeria's national production aspirations of 3.0 million barrels per day by 2030. This case study validates the imperative for 3D seismic control in complex structural settings prior to major capital commitments and demonstrates that exploration value creation extends beyond geological risk reduction to encompass operational, commercial optimization and economic justification. The systematic workflow provides a replicable framework for prospect maturation applicable to extensional tectonic settings in the Niger Delta and analogous petroleum basins globally.