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Abstract: Distribution, Origin and Prediction of Carbon Dioxide in Petroleum Reservoirs

Jane Thrasher, Andrew J. Fleet

High concentrations of carbon dioxide (CO2) in petroleum reservoirs can significantly reduce the value of the discovery, by diluting any hydrocarbons, and by increasing production costs because of the increased likelihood of corrosion and scale formation.

Huge volumes of CO2 have been found, for example in the Indonesian Natuna d-Alpha structure (estimated 240 tcf gas, of which around 70% is CO2. This study reviews the possible sources of CO2 in the petroleum system, and the geological and geochemical data from some CO2 'polluted' reservoirs, to improve future predictions of the exploration risk of finding significant CO2.

A number of case studies show that the most common geological circumstances for the occurrence of high concentrations of CO2 include: carbonates associated with post-trap igneous activity (e.g. Ibleo Platform, Sicily); reservoir close to hot basement (e.g. Cooper-Eromanga basin, Australia) and deep faults close to traps (e.g. Gulf of Thailand). Less common circumstances for high proportions of CO2 in gas include: post-trap igneous activity and coals (e.g. Taranaki, New Zealand) and reservoirs associated with pre-oil window coaly kerogen (e.g. Malay Trough), although the volumes of CO2 generated from kerogen are usually low relative to volumes of hydrocarbons generated from kerogen.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France