Introduction

Sub Basalt Exploration in Asia and Pacific

Basalt is present in a wide range of basin environments including mid-oceanic ridges, subduction zones and intra plate settings. There are large prospective areas of the world’s sedimentary basins that are still less explored for sub-basalt targets. Imaging below basalt has always been a challenge for exploration. Penetration of seismic energy below basalt has always been a problem, Strong inter-bed multiples always mask the weak reflections coming from sub-basalt formations. Severe scattering of seismic energy due to heterogeneity of basalt layer further complicates the problem which results in the lowering of frequency content of the data and also velocity model building for imaging becomes highly challenging.

These challenges can be addressed to certain extent using new processing technologies and focused strategies. Broadband processing may help in enhancing the low frequency signal content of the data. Advanced data driven demultiple techniques may help to eliminate the multiples below basalt to bring out the hidden signals. Velocity flooding approach may help in preparing a better velocity model for migration. Very long offset data and converted wave data are also being used for exploration of Mesozoics below basalt. New approaches like these are continuously being applied in the seismic industry and improvements are observed in the imaging below basalt. Workshop will address the challenges of Society Of Petroleum Geophysicists the seismic industry and improvements are observed in the imaging below basalt. Workshop will address the challenges of sub basalt exploration in Asia and Pacific.

Current Practise and Advance in Foothills Imaging

Foothills are generally characterized by difficult near surface and complex subsurface geology. Exploration in these areas is immensely challenging in terms of difficult logistics, complex subsurface geology of thrust belt and hilly terrains right from data acquisition through processing to integrated interpretation of the dataset.The complex near surface, large variation in elevation and high velocity exposures, not only affects the statics but also generate strong ground rolls which mask the limited subsurface illumination. This also means velocity model building has to be performed under a low signalto-noise condition in structurally complicated geological settings.

The conventional elevation statics based solutions do not provide the good results to handle above mentioned issues. Data driven statics computation approaches based on tomography derived refraction statics are able to handle the near surface irregularities more accurately. Horizon velocity analysis (HVA) provides the detailed lateral velocity variation along the marker horizon which may be missed by conventional velocity analysis that are sparsely spaced along the line. HVA is an efficient method to get velocity information at every CDP location along selected key horizons which will be structurally more consistent and geologically more conformable. Single arrival based Kirchhoff migration may have limitation in imaging due to subsurface complexity in such areas, necessitating the application of advance depth imaging techniques capable of using multi-arrivals of seismic energy.