271-9 Detection of Overpressured and Hydrocarbon-Bearing Zones Using the Normalized Second Harmonic Peak Index (NSHPI): Case Studies from the Illinois Basin and Offshore Nova Scotia.

Session: Geologic Energy Resources and Storage for Now and the Future (Posters)

Presenting Author:

Authors:

Abstract:

Reliable detection of overpressured intervals in the subsurface is critical for safe CO₂ injection and hydrocarbon exploitation. In this study, we implement and validate a novel seismic attribute Normalized Second Harmonic Peak Index (NSHPI) as a direct indicator of overpressurized and hydrocarbon-rich zones using post-stack seismic data.

Our primary application is the Illinois Basin Decatur Project (IBDP), where baseline 2011 seismic data were processed using the NSHPI workflow. NSHPI leverages advanced signal processing techniques including harmonic frequency analysis and instantaneous envelope extraction to quantify subtle spectral distortions in post-stack seismic data, particularly those linked to second harmonic generation caused by gas saturation or overpressure conditions. These predictions were cross validated through well pressure data and real-time monitoring. Remarkably, several zones identified by NSHPI as high-risk prior to injection were later confirmed to be overpressured during real-time monitoring, demonstrating the method’s predictive capability.

A second case study in offshore Nova Scotia demonstrated NSHPI's sensitivity to hydrocarbon-bearing formations. In this setting, the attribute successfully delineated known accumulations, validating its broader applicability to exploration and reservoir characterization.

The NSHPI processor integrates advanced spectral decomposition, envelope tracking, and statistical normalization within an efficient, scalable workflow. Its effectiveness across multiple geological settings confirms its value as a physics-informed, data-driven tool for early risk detection, subsurface screening, and fluid mapping using standard post-stack seismic data without requiring full waveform inversion or synthetics.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9550

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.