Universal Curves Describing the Chemical and Physical Evolution of Type II Kerogen during Thermal Maturation

This paper synthesizes and interprets literature data relating to the chemical and physical characteristics of kerogen (solid, insoluble sedimentary organic matter) representing more than a dozen petroliferous sedimentary basins across four continents, 400 million years of sedimentation, and burial histories ranging from thermally immature to overmature. The studied kerogen properties include chemical composition (elemental composition and carbon and heteroatom speciation), physical properties (skeletal density), nuclear responses (petrophysical properties), and microstructure (surface area). As occurs in the vast majority of economically significant conventional and unconventional petroliferous sedimentary basins, the kerogens are observed to be predominantly or entirely paleo-marine (derived from marine plankton and algae) and classified as so-called type II kerogen. The analysis described here reveals that that the wide range of chemical and physical properties of type H kerogen is explained nearly entirely by its extent of thermal maturation and is independent of basin location, age, and other basin-specific characteristics, such as formation lithology. The analysis results in a series of universal curves relating many type H kerogen properties to thermal maturity, with correlation coefficients typically of 0.85-0.90. The indistinguishable property-maturity relationships among type II kerogen in petroleum-bearing formations globally make it possible to infer its relevant chemical and physical characteristics only from knowledge of the thermal maturity of the organic matter. As shown by example, this presents substantial practical benefit for unconventional shale exploration and appraisal because chemical, physical, and petrophysical properties of kerogen are critical in such workflows but are nearly always unknown and otherwise impractical to measure in typical industrial projects.