Impact of formation water geochemistry and crude oil biodegradation on microbial methanogenesis

Organic Geochemistry
By: , and 

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Abstract

Converting non-producible crude oil to CH4 via methanogenic crude oil biodegradation in oil reservoirs could serve as one way to increase our energy profile. Yet, field data supporting the direct relationship between methanogenesis and crude oil biodegradation are sparse. Indicators of methanogenesis, based on the formation water and gas geochemistry (e.g. alkalinity, δ13C–CO2) were compared with indicators of crude oil biodegradation (e.g. pristane/phytane and n-alkane ratios) from wells in the Wilcox Group of Louisiana to determine if increases in extent of methanogenesis were related to increases in extent of crude oil biodegradation.

Shallow wells (393–442 m depth) contained highly biodegraded oils associated with low extent of methanogenesis, while the deepest (> 1208 m) wells contained minimally degraded oils and produced fluids suggesting a low extent of methanogenesis. Mid-depth wells (666–857 m) in the central field had the highest indicators of methanogenesis and contained moderately biodegraded oils. Little correlation existed between extents of crude oil biodegradation and methanogenesis across the whole transect (avg.R2 = 0.13). However, when wells with the greatest extent of crude oil biodegradation were eliminated (3 of 6 oilfields), better correlation between extent of methanogenesis and biodegradation (avg. R2 = 0.53) was observed. The results suggest that oil quality and salinity impact methanogenic crude oil biodegradation. Reservoirs indicating moderate extent of crude oil biodegradation and high extent of methanogenesis, such as the central field, would be good candidates for attempting to enhance methanogenic crude oil biodegradation as a result of the observations from the study.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Impact of formation water geochemistry and crude oil biodegradation on microbial methanogenesis
Series title Organic Geochemistry
DOI 10.1016/j.orggeochem.2016.05.008
Volume 98
Year Published 2016
Language English
Publisher Elsevier
Contributing office(s) Eastern Energy Resources Science Center
Description 13 p.
First page 105
Last page 117
Online Only (Y/N) N
Additional Online Files (Y/N) N