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Eilrich, Bernd1, Armin Kauerauf1
(1) IES Integrated Exploration Systems, 52428 Juelich, Germany

ABSTRACT: Methane Carbon Stable Isotopes in Petroleum Systems: PVT Controlled Migration and Reservoir Modeling

Full PVT (pressure, volume, temperature) control represents a powerful new tool for modeling the generation and migration of hydrocarbons and their evolution over long time spans (10s to 100s m.y.). Methane is a primary constituent of reservoir fluids and occurs with two stable carbon isotopes, 12C-CH4 and 13C-CH4. The major transport mechanisms for methane are diffusion and percolation as a dissolved species through the pore space of the sediments. Isotope fractionation is a consequence of the different diffusion and dissolution behavior of 12C-CH4 and 13C-CH4.
This study reports the simulation results for a simple petroleum system. Deterministic numerical forward modeling was performed with a new approach: Flash calculations allowed accurate determination of PVT conditions for the assigned simulation time steps. A simple geometry and typical source, carrier, and reservoir lithologies were chosen. While the distribution of activation energies as the main kinetic parameter was kept constant, transport parameters (e.g. diffusivities) differed for 12C-CH4 and 13C-CH4. The observed isotope patterns reflect the isotope fractionation over long time spans. They are different for the different lithologies and therefore point to the strong influence of permeability, and hence the compaction history of the basin. The results of modeling may contribute to efficiently tracing back preferred migration pathways for methane and higher hydrocarbons.
The influence of the different transport mechanisms to isotope fractionation is compared to laboratory and model data obtained for near-surface methane occurrences in unconsolidated sediments.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.