TITLE:
Hidden Potential: The Impact of Seismic Tuning on Gas Volumes Estimation: Case Study of a Tertiary Reservoir, Onshore Niger Delta
AUTHORS:
Chibueze Amadi
KEYWORDS:
Bonn-Ario, Tuning, Frequency, Seismic, Wedge Modelling, Forward Modelling
JOURNAL NAME:
Open Journal of Geology,
Vol.15 No.11,
November
27,
2025
ABSTRACT: Seismic amplitude anomalies are widely used as direct hydrocarbon indicators (DHIs) to infer fluid contacts where well control is sparse, yet seismic tuning can bias amplitude-derived fluid contacts and volumetric estimates towards conservatism. We analyze the M1000 gas reservoir in the Bonn-Ario field (onshore Niger Delta) to quantify how tuning-driven effects produce an apparent seismic gas-water contact (GWC) that underestimates the true gas column. Using forward modelling, amplitude variation with angle (AVA) analysis and wedge models, we show that amplitude “shut-off” on the seismic corresponds to a tuning roll-off rather than the physical termination of reservoir gas; tuning effects produced a seismic-derived GWC that would reduce gas initially in-place (GIIP) by ~15% relative to a well log-constrained contact. Wedge modelling indicated that amplitude dimming becomes dominant below ~35 ft of gas column for the local wavelet and velocity. The seismic response effectively fails to detect a gas column thinner than ~35 ft. Analogous examples from the Niger Delta and other basins confirm that this mechanism is widespread. We demonstrate practical mitigation: routine forward-modelling, AVA calibration and wedge modelling to identify tuned intervals and avoid systematic under-booking of volumes. The study highlights that amplitude maps should be treated as λ/4-contour (resolution) indicators, rather than fluid contact proxies, unless verified by wedge modelling, AVA analysis and well calibration. Emerging technologies such as broadband seismic acquisition, machine learning and multi-attribute analysis provide additional toolbox for mitigating tuning-related pay and volumetric mis-estimations.