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Scaling Analysis of the Coupled Compaction, Kerogen Conversion, and Petroleum Expulsion During Geological Maturation

Abstract

Porosity rebound is associated with the kerogen conversion into hydrocarbons and the overpressure development in the coupled sedimentary compaction, kerogen conversion, sorption, and fluids expulsion processes. There are a large number of variables with uncertainties, which affect the porosity rebound and overpressure. Uncertainty analysis to determine their sensitivity and importance via 3D basin-scale simulations is very time-consuming. To address this problem, we developed a simple but efficient model and performed scaling analysis to identify the relative importance of each mechanism/parameter. We then reduce the number of parameters to the most essential in controlling porosity rebound and overpressure. The procedure is to first develop a unit cell model by considering elastic and inelastic deformation of solids, thermal expansion, primary and secondary cracking, sorption of hydrocarbon, and fluid expulsion. Inspectional analysis is then employed to obtain dimensionless equations as well as dimensionless numbers. The competing mechanisms for porosity rebound and overpressure development are represented by several dimensionless numbers. A two-level experimental design is then conducted to generate the combinations of all dimensionless numbers and corresponding scenarios. Through this research, we have reduced the variables from 53 physical parameters to 43 dimensionless numbers, out of which only 9 have the largest impact on porosity rebound. The ranking of the most important parameters associated with the dimensionless numbers follows: initial kerogen content, geothermal heating rate, compaction coefficient, fluid expulsion rate, reaction rate, and gas fraction in generation. For overpressure, the ranking is different but involves the same 9 dimensionless numbers. The results are verified against PetroMod simulations. We expect this work to provide useful guidelines in greatly simplifying analyses and simulations in basin modeling.