Model for How Microbial Methane Generation can Preserve Early Porosity in Dolomite and Limestone Reservoirs Geohorizons

Model for How Microbial Methane Generation can Preserve Early Porosity in Dolomite and Limestone Reservoirs Geohorizons

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  • November 20, 2018
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In some dolomite and limestone hydrocarbon reservoirs, protection from cementation is a primary factor in porosity preservation. We present a model in which methanogens (methane-producing microorganisms) produce methane gas (CH 4 [g]) that outgasses from solution in pore space, creating a two-phase system that reduces effective hydraulic conductivity (K), protecting pore space from cementation. Methanogens have been implicated in dolomite formation and can generate methane to fill pore space of a model near-surface carbonate sediment (37.5% primary porosity) with CH 4 (g) in 180 to 4650 yr, depending on nutrient levels. Gas generation results in occlusion of the aqueous phase from pore spaces and throats, creating a two-phase flow regime, reducing the effective hydraulic conductivity of model marine carbonate sand by about 50%(from 2.8 to 1.2 cm/day) in as little as 55 yr, therefore reducing …

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