The Impact of Coal on AVO Interpretation in the Tertiary Basins of Southeast Asia

Lignite coal is abundant in the paralic sequences of many of the Tertiary Basins of Southeast Asia. These coals are often interbedded with hydrocarbon bearing rocks. Exploration for and development of these hydrocarbon resources through seismic amplitude analysis is challenging. The coals have elastic properties that are very different from other rocks deposited in these environments to the extent that they can dominate seismic sections even though they represent a small fraction of a sequence. Their extreme values also cause attenuation, the generation of strong intra- and inter-bed multiples, and mode conversions. Removal or exploitation of energy that does not conform to the convolutional model is complicated even when intrinsic attenuation and anisotropy are not considered. Were it possible to process seismic data with a high degree of consistency to the convolutional model, the extreme properties of irregularly spaced and variably thin coals with highly variable clay content makes interpretation of seismic amplitude variation with offset (AVO) for hydrocarbon presence highly uncertain.