Abstract:

In Malay - Tho Chu basin, CO2 gases were found with content ranging from few up to 66% by volume. The CO2 gas amounts increase with depth, CO2 - rich gases mainly concentrate in I and J sequences from depth of 3000m in the North and 1500m in the South. The gases in this basin could be divided into two groups: Group 1 is hydrocarbon - rich, typically containing 65 - 85% hydrocarbons and less than 20% CO2; Group 2 is CO2 - rich, containing 22 - 66% of CO2 in total gases. The hydrocarbon gases are quite dry because of methane predominance composition and have thermogenic origin. On the other hand, CO2 gases have both organic and inorganic origins. The organic CO2 gases showing low - CO2 content are characterized by a lighter δ13CCO2 varying from - 17.8‰ to - 10.8‰. The inorganic CO2 gases make up high content and occur at deeper reservoirs. These CO2 gases are isotopically heavy with δ13CCO2 values from - 9.3‰ to 0.5‰. The large amount of CO2 gases in Malay - Tho Chu basin is believed to be generated from the mineral thermal decomposition which occurred in the deep troughs as Tho Chu graben and central trough of Malay basin with depth of over 14km