Coal and coal-bearing strata as oil-prone source rocks: an overview

Despite many advances in our knowledge over the last decade, understanding of why some coals and coal-bearing strata are oil prone, and our ability to predict such sequences ahead of drilling in petroleum exploration, is relatively poor. Here we review the current status of the knowledge, highlighting contributions made in this volume. Oil-prone coals are hydrogen rich. Those which are generally acknowledged to have given rise to significant oil accumulations occur either as low latitude Tertiary deposits or within late Jurassic-Palaeogene sequences of the Australian region. Oils derived solely from coals and other terrigenous kerogens can be recognized using geochemical criteria. Recognition of oil-prone coals and associated mudrocks visually or geochemically, however, is problematical. What controls the expulsion of petroleum in the liquid phase from coal-bearing sequences is probably the critical factor. Our knowledge of the botanical, depositional and diagenetic controls which determine the formation of oil-prone coaly sequences, and hence our ability to predict their presence, is currently empirical and lacks understanding of the inputs and processes involved.