Publications

As the pace of gas exploration and development increases in Indonesia, the problem of encountering CO2 and its subsequent impact on economic development of reserves has come sharply into focus. Not only does the amount of CO2 affect the volume of recoverable hydrocarbon reserves, but expensive separating plants also put up the cost of development. Consequently, an understanding of the factors controlling the occurrence of CO2 is of major economic importance. This paper presents the results of a study on the origin and distribution of CO2 in western Indonesia.Subsurface formation of CO2 can occur by a variety of organic and inorganic processes and it is quite possible that more than one process is active in any given area. The interpretation of the ultiniate source(s) of CO2 presented here is largely based on J13C analyses of CO2 from gas/oil fields. However, such analyses rarely give unambiguous results. Such ambiguity can occur for a number of reasons. Some CO2 sources do not have a unique isotopic signature.Additionally, chemical reactions taking place during migration can modify not only CO2 concentrations, but also the isotopic signature of the CO2. Lastly, mixing of CO2 from different sources with different isotopic signatures can confuse matters. By considering 8°C values of CO2 in conjunction with the occurrence of other non-combustible gases, such as He and N2, and the geology of an area, more precise interpretations of the origin of CO2 can be made.Typically, the site of CO2 production is not the site of its accumulation. It is prone to migration just as hydrocarbons are. Geological analysis of individual basins in western Indonesia has helped to identify migration pathways and barriers to movement.By understanding the origins of CO2 and the factors controlling its migration it has been possible to predict CO2 occurrence with some confidence in western Indonesia. Although the study considered a limited area, its results are probably applicable on a wider regional scale.