Barry Bennett

The effect of biodegradation and water washing on the occurrence of alkylphenols in crude oils

Abstract Biodegraded oils from California and Nigeria were analysed to assess the impact of biodegradation upon alkylphenol occurrence in crude oils. The extent of biodegradation in the 13 Californian samples ranged from very mild (full n -alkane distribution present) to moderate (complete degradation of C 15 + n -alkanes and significant reduction of acyclic isoprenoids) corresponding to a range of n -alkanes and acyclic isoprenoids (stage 5). The data from the naturally-degraded sample suites were compared to the results of an in-vitro aerobic biodegradation experiment conducted with a North Sea oil. Biodegradation resulted in significant reduction in total alkylphenol abundance and preferential depletion of C 3 and C 2 alkylated compounds in the Nigerian and laboratory degraded samples. These effects were most pronounced in oils in which the methylated naphthalenes had been biodegraded (biodegradation stage 4 or 5). There was no clear relationship between alkylphenol abundance or molecular distributions and the extent of biodegradation in the Californian samples, although alkylphenol distributions in the biodegraded samples were generally dominated by the C 3 compounds. Simple oil/water partition calculations showed that these distributions were consistent with the effects of water washing.

An experimental investigation of geochromatography during secondary migration of petroleum performed under subsurface conditions with a real rock

An understanding of the size of petroleum secondary migration systems is vital for successful exploration for petroleum reserves. Geochemists have suggested that compositional fractionation of petroleum accompanying the migration process (geochromatography) can potentially be used to infer distances petroleum may have travelled and the ratio of oil in the reservoir to that lost in the carrier. To date, this has been attempted by measuring concentrations and distributions of specific steranes, and aromatic oxygen and nitrogen compounds in reservoired oils which have been proposed to respond to migration rather than to source maturity or other effects. We report here an experiment involving oil migration through an initially water wet siltstone under realistic subsurface carrier bed or reservoir conditions (48 MPa, 70°C) where source facies and maturity effects are eliminated. We show that geochromatography does indeed occur even for initially water-saturated rocks and that the migration fractionations observed for alkylcarbazoles, benzocarbazoles and alkylphenols are very similar to those seen in field data sets. In contrast, sterane based migration parameters show no compositional fractionation under these conditions.

From Syntropic Bacteria to Beyond SAGD! The Origin & Impact of Oil Viscosity Variations in Heavy Oil Reservoirs & Routes to Low Carbon Emissions Energy Recovery

The recently discovered anaerobic biological conversion of liquid petroleum hydrocarbons to methane in oil reservoirs (methanogenesis), on geological timescales, occurs through biological action by syntrophic bacteria and methanogenic archaea at temperatures as low as 15°C(Head et al., 2003; Jones et al., 2008). As the oil is destroyed from the bottom of the oil column, large vertical and lateral gradients in oil viscosity are formed which impact optimal placements of wells for oil recovery (Larter et al, 2008). Understanding the biodegradation process that produces heavy oil and methane offers great potential both to improve recovery of existing heavy oil resources, through more efficient use of energy during oil recovery and also, potentially, to move away from oil recovery as the major energy process entirely! The discovery of the MADCOR process (Methanogenic Alkane Degradation by Carbon Dioxide Reduction), as it has been termed, raises many possibilities for reduced emission to atmosphere energy recovery (REAR) processes as methane is quantitatively produced from biodegraded alkanes, utilising water as co-reactant, with large amounts of molecular hydrogen being a principal intermediate (Jones et al., 2008).