Scaling analysis of coupled compaction, kerogen conversion, and petroleum expulsion during geological maturation

Porosity is an important property of source rocks with implications on petroleum storage and expulsion. The evolution of porosity over geologic time-scales is controlled by coupled processes such as compaction, geothermal heating, kerogen kinetics, and fluid flow. Basin-scale models used to predict the evolution of porosity contain a large number of interdependent parameters. This poses a significant challenge on numerically solving the complex system of equations in field-scale simulators as well as quantifying the uncertainty induced by each parameter. Our objective is to identify the dominant mechanisms that control porosity evolution using scaling analysis. We develop a single-cell model that, despite simplifications, captures all important processes driving the physics, e.g., thermal, mechanical, chemical, sorption, and multi-phase flow. We then identify a minimum set of dimensionless numbers, each associated with a term in the governing equations, that have first-order impact on porosity evolution during primary and secondary cracking of kerogen. The insights here can be used to reduce the dimensionality of basin-scale models and to quantify uncertainty.