Integrated Seismic Processing challenges in Karstified terrain of PNG Fold Belt

Abstract

Seismic exploration in the Papua New Guinea highlands poses many challenges from both an acquisition and processing standpoint. Severe operational constraints combined with highly variable surface and subsurface geology, push established seismic techniques to the very limit of their underlying principles. Remote location, rugose terrain, severe weather conditions and local stakeholder relations are just some of the numerous factors that restrict operations and limit optimal data acquisition. Other technical issues include complex sub-surface structure, karstified limestone, velocity inversions, and extreme topography. Complex geological structures, rough topography, huge lateral velocity changes and variable source attenuation across different geological settings are the main causes of poor signal-to-noise in the acquired seismic data. Optimal imaging of land seismic data, particularly in PNG, require two primary issues to be addressed; 1) the effect of near surface layers on arrival times and 2) the attenuation of strong coherent noise. Velocities of the near surface layers are generally determined by refraction statics analysis. Various refraction statics analysis methods to determine the optimum statics values have been trialled across PNG. Repeated trials have shown that first arrival time (FAT) based refraction tomography generally provides the most robust results for near surface velocity and static determination. Another advantage of using the tomographic technique is that it allows much more flexible models which correspond with the geologic model. Once the optimum statics values are obtained, various noise types in shot gathers are tackled carefully with optimised signal processing techniques in different domain. Final velocity models are created iteratively using the cleaned shot records for input to migration. To summarize, Oil Search has progressively improved its ability to extract maximum interpretable value out of the complex and noisy seismic datasets of Papua New Guinea. This has been achieved through the optimisation of Static Modelling, Noise Attenuation, Migration Methodology and Stack Image Enhancement .

AAPG Datapages/Search and Discovery Article #90371 © 2020 AAPG Asia Pacific Region, The 1st AAPG/EAGE PNG Geosciences Conference, PNG’s Oil and Gas Industry: Maturing Through Exploration and Production, Port Moresby, Papua New Guinea, February 25-27, 2020