Regrounding Geophysical Fundamentals: Establishing Volumetric Assurance through Seismic Petrophysics

As hydrocarbon discoveries become increasingly complex, this study highlights the importance of revalidating exploration assumptions through geophysical fundamentals during development planning. Focusing on a newly discovered gas field (“M Field”), the study integrates Amplitude Variation Offset (AVO) analysis, rock physics modeling, fluid substitution, and pressure data calibration across several gas-bearing reservoirs. Initial interpretations suggested hydrocarbon upside beyond seismic amplitude conformance, but Quantitative Interpretation (QI) revealed predominantly Class III AVO responses aligned with pressure-derived gas-water contacts (GWCs), affirming the reliability of Direct Hydrocarbon Indicators (DHIs). Some zones displayed Class IIp or Class I responses, showing seismic variability across reservoirs. In Reservoir E2, integrated analysis of seismic attributes, petrophysical properties, and pressure data confirmed a GWC shallower than seismic conformance. Reservoir E1 presented fizz gas effects, increasing interpretation complexity. The combined analysis reduced GWC uncertainty, leading to <10% volumetric variance between exploration and development estimates. This study underscores the risk of overestimating volumes by relying solely on DHI amplitude and advocates for integrated, technically grounded interpretation workflows. Recalibrating seismic interpretation with petrophysical and pressure data enhances volumetric accuracy and builds confidence in field development planning.