A GEOCHEMICAL METHOD FOR ASSESSMENT OF THE THERMAL HISTORIES OF SEDIMENTS: A TWO-WELL CASE STUDY FROM THE GIPPSLAND BASIN, AUSTRALIA

Abstract

The ester content in kerogen is depleted as sediment maturation progresses in a process which has been shown to correlate with change in the carbon preference index (CPI) of the associated soluble organic matter. We have carried out accurate laboratory measurements of the kinetics of the reaction which causes ester depletion in sediments, and we show how this information can be used to assess the thermal history of sediments. Two wells were selected, Grunter-1 and Volador-1, to provide samples from the Latrobe Group in the Gippsland Basin. The CPI values were measured to assess the extent of reaction at points down each well, and these values were then used with the kinetic parameters for the ester depletion process to obtain thermal histories which are consistent with the available maturity information.

This treatment enabled the heat flow from 50 Ma to the present to be assessed and it suggests that at both locations a constant low heat flow during the Gippsland stable phase was followed by a gradual increase from the beginning of the Miocene to present-day values.