CAO, SONG, and IAN LERCHE, University of South Carolina, Columbia, SC

ABSTRACT: Thermal History Reconstruction by Inversion of S2 Pyrolysis Data: Synthetic Studies and Case Histories

Thermal history reconstruction, as seen by buried kerogen samples,

relies upon both a kinetic scheme for kerogen break-down in the sub-surface as well as paleoheat flux information. A numerical model to invert S2 data from routine Rock-Eval pyrolysis was developed and tested against synthetic data sets and real data from two wells.

The synthetic tests show that the S2 inverse model is sensitive to the present day heat flux (Q<0>), to parameters describing paleoheat flow, to the number of probability channels for activation energy, and to the range of activation energy. The synthetic tests also show that for a given S2 data set, there can be different sets of kinetic parameters which give not only the same degree of fit between the calculated and measured S2 values, but also similar S2 evolution patterns with burial paths, i.e, there is no unique kinetic solution for a given set of S2 data.

The applications of the S2 inverse model to two real well data sets show that the S2 data can be used as a thermal indicator to determine the paleoheat flow and that the results are as useful as those from other thermal indicators, provided high quality S2 data are available. For an S2 data set with a mixture of kerogen types it is first necessary to perform an un-mixing procedure prior to using the inverse model in order to obtain equivalent single type kerogen contributions or else results obtained will not be trustworthy.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.