--> --> Modelling Biogenic Gas Generation and Migration – Application on the Levantine Basin

AAPG Africa Region, The Eastern Mediterranean Mega-Basin: New Data, New Ideas and New Opportunities

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Modelling Biogenic Gas Generation and Migration – Application on the Levantine Basin

Abstract

Methanogenic biodegradation of Sedimentary Organic Matter (SOM) has recently focused the interests of the O&G industry following the growing demand on natural gas and the discovery of giant biogenic methane accumulations (Levant, Tamar field, …). In order to model biogenic gas generation and migration, new functionalities have been developed by IFP Energies nouvelles within basin simulator TemisFlow™. First, the total labile organic matter was split into three distinct fractions: a first fraction that micro-organisms can directly metabolize and controlled by a degradation rate which is a function of microbial activity, a second fraction (labilizable) for which a previous thermal transformation, controlled by an Arrhenius equation, is necessary, and a third fraction, refractory. Consequently, temperature has a strong impact on biogenic methane generation since it controls both the bacterial activity and the transformation rate from labilisable to labile organic matter. The methane produced in the model is allowed to be distributed in three states: 1) adsorbed onto SOM, 2) dissolved in formation brine and 3) as a free gas phase. The methane is transported in the model by the effects of burial and compaction, whereby the production and distribution of biogenic methane is fully coupled with dissolution and advection mechanisms, and is then allowed to migrate as a dissolved compound in water but also as a free gas phase. Since the model parameters have been determined at low scale, an upscaling work is essential to use this model at basin scale. The effects of the different generation laws are submitted to a sensitivity analysis. Recommended values are defined based on natural 1D cases corresponding to the geological history of LEG175 (Benguela upwelling, offshore Namibia). Finally, the model of biogenic gas production and migration implemented has been used on a 2D section of the Levantine basin showing the distribution of adsorbed, dissolved and free gas along the geological history. A particular focus is made on the effect of the messinian crisis on the evolution of the gas distribution.