THERMAL HISTORY RECONSTRUCTION BY INVERSION OF DOWN-HOLE S2 PYROLYSISDATA - SYNTHETIC STUDIES AND CASE-HISTORIES

Thermal history reconstruction, as seen by buried kerogen samples, rel ies upon both a kinetic scheme for kerogen break down in the sub-surfa ce as well as paleoheat flux information. A numerical model to invert S2 data from routine Rock-Eval pyrolysis was developed and tested agai nst synthetic data sets and real data from two wells. The synthetic te sts show that the S2 inverse model is sensitive to the present day hea t flux (Q0), to parameters describing paleoheat flow, to the number of probability channels for activation energy, and to the range of activ ation energy. The synthetic tests also show that for a given S2 data s et, there can be different sets of kinetic parameters which give not o nly the same degree of fit between the calculated and measured S2 valu es, but also similar S2 evolution patterns with burial paths, i.e. the re is no unique kinetic solution for a given set of S2 data. The appli cations of the S2 inverse model to two real well data sets show that t he S2 data can be used as a thermal indicator to determine the paleohe at flow and that the results are as useful as those from other thermal indicators, provided high quality S2 data are available. For an S2 da ta set with a mixture of kerogen types, it is first necessary to perfo rm 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.