RECENT ADVANCES IN BURIAL AND THERMAL GEOHISTORY ANALYSIS

Abstract

Geohistory analysis is a technique for plotting the cumulative subsidence of various chronostratigraphic horizons encountered in an exploration well or section. The intervals between horizons are corrected for sediment compaction and are plotted relative to an estimated ancient seabed (or land surface) as a function of geological time. Speed and precision have been added to this procedure by automatic computer processing and plotting. A variable eustatic sealevel datum has also been introduced. Accurate quantitative assessment of depth sub-seabed (or subsurface) of any horizon may be combined with a model of heatflow history for the well location to compute a maturation integral and theoretical vitrinite reflectance for that horizon as a function of geological time. Comparison of theory with present observations may be used to refine the model heatflow history. Palaeomaturation may be readily assessed.

An offshore Perth Basin example is used to illustrate the effects of palaeosealevel, palaeoheatflow and unconformities and hiatuses. Analysis of a cross-section through three wells is used to demonstrate the potential for accurate calculation of a palinspastic section, palaeomaturation and migration direction. Geohistory analysis is demonstrated to be an essential tool in rigorous basin evaluation.