ABSTRACT

The vitrinite reflectances (%R_o) of well-cutting samples from two wells from the Liard Basin range from 0.26 to 4.6 and display a uniform downhole increase. Similarly, R_o values for a well in the Interior Plains immediately east of the Liard Basin increase downhole from 0.58 to 2.00. Other maturation indicators, such as T_max from Rock-Eval data, percentage of mixed layer clays, illite crystallinity data, reflectance of bitumens, conodont alteration indices (CAI), and palynomorph thermal alteration indices (TAI) from both well and outcrop samples provide independent verification of the vitrinite reflectance profiles. The reflectance profiles of the post-Silurian Phanerozoic sequence in the Liard Basin and the Interior Plains provide a basis for the determination of the history of organic thermal maturation. The contrasting burial history of the Liard Basin versus the Interior Plains and fluid inclusion homogenization temperatures from minerals precipitated during burial provide constraints on possible model solutions for the burial and thermal history of these wells, provided that the entire region underwent a similar history of heat flow fluctuation.

A thermal event in Late Devonian time, as suggested by previous workers, provides the most consistent interpretation for the observed vitrinite reflectance profiles for each of these wells and for the fluid inclusion data. Other hypotheses, one involving a time invariant or uniform heat flow, and the other involving a Tertiary event of high heat flow, provide less consistent fits with the observed data. Migration of liquid hydrocarbons probably occurred in late Paleozoic to early Mesozoic time regardless of temporary heat flow perturbations. The bitumen-bearing Manetoe gas field reservoirs in the Liard Basin must have formed before hydrocarbon generation and migration in order to have received these hydrocarbons. This is consistent with the suggestion of previous workers that the Manetoe Facies formed in Late Devonian time.

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