--> Abstract: Novel Technologies for Determining the Charge History and Bio-degradative Losses in Heavy-oil Oilfields, by Moldowan, John M. and Denisevich, Peter; #90166 (2013)

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Novel Technologies for Determining the Charge History and Bio-degradative Losses in Heavy-oil Oilfields

Moldowan, John M.1 and Denisevich, Peter
1[email protected]

Geochemists are often asked to address three factors that can influence the economics and producibility of heavy oil. (1) Determining the amount of oil lost from an accumulation compared to the pristine oil that originally entered the oilfield is one important question in heavy oil economics. (2) Reservoir barriers to production are a second concern. Because biodegradation is likely to progress differently in non-communicating portions of reservoirs, differences in biodegradation history can be used to determine reservoir communication. (3) Oil charges that enter an oilfield can be biodegraded to various extents, depending on the timing of charge versus closure of traps and seals, and the availability of nutrients to support growth of the degradative microorganisms. Regional exploration strategies and modeling for oilfield development could be improved by a better understanding of these processes.

Biomarker acids were analyzed in a sequence of oil samples from California in order to calibrate their appearance and disappearance at various levels of biodegradation severity. Their occurrence was calibrated against the biodegradation ranking scheme of Peters and Moldowan from "The Biomarker Guide", first edition. Specific biodegradation levels result in the occurrence or absence of specific biomarker acids and their relative concentrations trace the history of biodegradation of the oil charges that formed the accumulation. In total, a semi-quantitative assessment of the charges to a biodegraded oilfield can be made. Reservoir continuity and oilfield history can be derived from these data when applied across a reservoir or oilfield, respectively.

The relative biodegradation and charging histories of oil samples from the Orinoco heavy oil belt of Venezuela were determined by using biomarker acids and traditional biomarker assessment methods. An estimation of oil quantities (percentages) lost through biodegradation is proposed for each oil reservoir represented by an oil sample. The estimation is made by using diamondoid-based technologies in concert with the biodegradation assessments made by using biomarkers and biomarker acids. Diamondoids are a compound class that is largely inert to biodegradation, and thereby, diamondoids act as an internal standard in biodegraded oil to quantitatively estimate the losses of the biodegradable portion of the oil.

 

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013