Integrated Qualitative and Quantitative Evaluation of Depositional Environment and Hydrocarbon Prospectivity of the QX Field in Southeastern Niger Delta

Abstract

Exploration in the Niger Delta has matured over decades, yet predicting reservoir quality in newly discovered marginal fields remains uncertain due to persistent subsurface heterogeneity and facies variability. In fields like QX, this uncertainty translates into real investment risk, largely because many existing studies rely on either petrophysical or stratigraphic interpretations in isolation. This study addresses this gap by integrating seismic data, well logs, and sequence stratigraphic frameworks into a unified qualitative–quantitative workflow aimed at improving depositional interpretation and hydrocarbon prediction. Three reservoirs (RES1, RES2, and RES3) were identified and characterized across the field. The combined petrophysical and sequence stratigraphic analysis reveals a progressive depositional architecture, with RES1 and RES2 formed within channelized shoreface systems, while RES3 reflects a lower shoreface setting. Two third-order depositional sequences and their associated system tracts were delineated, establishing a clear stratigraphic linkage from RES3 at the base to RES1 at the top. This integrated approach not only constrains facies distribution but also improves confidence in reservoir continuity and fluid prediction. Reservoir quality indicators show favourable conditions, with net-to-gross values of 69.25–84.75%, porosity ranging from 19.50–25%, shale volume between 12.20–30.75%, and water saturation of 27.94–41.75%. Permeability values (59.68–152.51 mD) further support good reservoir deliverability. Volumetric estimates derived from both deterministic and simplified probabilistic methods provide a more balanced assessment of uncertainty, yielding STOIIP values of 6.13 MMSTB (P50) for RES1 and 58.27 MMSTB (P50) for RES3, alongside GIIP estimates of 2.66 BCF and 9.54 BCF for RES1 and RES2, respectively. Notably, RES2 is interpreted as a gas-bearing unit sandwiched between oil-bearing RES1 and RES3. In all, the QX Field is estimated to contain approximately 64.40 MMSTB of oil and 12.20 BCF of gas. Beyond these volumes, the study demonstrates that integrating depositional architecture with quantitative petrophysical evaluation significantly reduces uncertainty in reservoir prediction. This has practical implications for decision-making in marginal field development, offering a more reliable basis for reserve estimation, risk reduction, and field planning in complex deltaic systems.