Like Space and Time, Transformation Ratio is Curved

Abstract

Source rock kerogen hydrogen indices and transformation ratios are frequently used as thermal maturation surrogates, and as proxies for calculating the amount of hydrocarbons generated from a thermally mature source rock, assuming an original hydrogen index can be assigned to the source rock. Transformation ratio (TR) and hydrogen index (HI) are commonly assumed to be linearly related via TR = (HIo – HI)/HIo, where HIo is a constant – the immature source rock's average original hydrogen index – and HI is the present day hydrogen index. In reality, however, the TR-HI relationship is shown to be non-linear. That non-linearity manifests itself most markedly in highly oil-prone, high original HI source rocks, which has important petroleum exploration implications. For example, an area where the present day HI is ~550 for an oil-prone source with HIo = 700 would traditionally calculate at a TR = ~20%. However, its true TR is ~40%. Therefore, areas where the source transformation ratio has traditionally been calculated as too low to have generated / expelled commercial amounts of hydrocarbons may in fact have transformation ratios which do imply significant hydrocarbon generation and expulsion. Examples and application are presented.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015