The Thermal Evolution of Solid Bitumens, Bitumen Reflectance, and Kinetic Modeling of Reflectance: Application in Petroleum and Ore Prospecting

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Abstract
This article is concerned with (1) the prevailing chemical processes involved in the thermal evolution of sulfur-rich and -poor solid bitumens, represented by the “type locality” wurtzilite and albertite, (2) the reflectance evolution of solid bitumens and its relationship to vitrinite reflectance, and (3) the application of bitumen reflectance and bireflectance in estimating the palaeothermal conditions in the petroleum- and ore-bearing sediments. The thermal evolution of wurtzilitelike bitumens will result in depolymerization and formation of petroleum-soluble molecules. The thermal evolution of albertite will result in the formation of increasingly condensed, petroleum-insoluble residues. Broadly speaking, the response of albertitelike bitumens to maturity increase is similar to that of kerogen. A kinetic model of relevance to petroleum exploration, calibrated by geological and laboratory data, was designed. The model shows that the bitumen-vitrinite reflectance relationship is insensitive to the heating rate conditions. The calculated kinetic parameters show that the peak reflectance change of bitumen is shifted to higher activation energies compared to the coal vitrinite, and to lower activation energies compared to the marine shale saprovitrinite. The opinion that albertite is the result of the maturation of wurtzilite is in error. Bulk structural models for albertite- and wurtzilitelike bitumens and for their thermally altered residues are proposed. The role of sulfur bridges in the rapid release of hydrocarbon structures at low activation energies is considered important. Finally, the reflectance-bireflectance relationship of bitumensipyrobitumens and its application in ore prospecting are discussed.