ZHAN, XIAOYONG, ANTHONY J. PARK, DOROTHY F. PAYNE, KAGAN TUNCAY, and PETER J. ORTOLEVA
Laboratory for Computational Geodynamics, Indiana University, Bloomington, IN

Abstract: Predictive Modeling of Natural Gas Composition in Reservoirs

Predicting in-situ gas-phase composition is beneficial for assessing the quality of potential natural gas resources.

Specifically, excess CO₂ can diminish the quality of methane reserves and render them uneconomic. To address this problem, we have developed a three-dimensional multi-phase flow model, which accounts for the generation, expulsion, transport and specific partitioning of CO₂ and CH₄.

Gas composition is affected by several factors. Rates of gas production are functions of the decarboxylation and methanogenesis kinetics, the composition of the source material, and the thermal history. Once the gases are generated, the difference in solubilities of CO₂ and CH₄, and their strong temperature dependences will affect the relative gas saturations. The gas composition may also affect the flow path, as it changes the surface tension between the gas and aqueous phases, which alters the capillary pressure.

In our model, gas generation rates are obtained from a newly developed methanogenesis model. Multi-phase flow processes are included in the CIRFB reaction-transport-mechanical simulator which accounts for rock deformation, heat flow, and diagenesis. Our model is shown to be effective in predicting natural gas quality, and is applied to predict natural gas composition in U.S. onshore basin.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas