On the Origin, Distribution, and Size of Natural CO2 Accumulations and Implications for CH4 Exploration and Development on Continental Margins

Tip Meckel¹ and Lawrence Meckel²
¹ Texas Bureau of Economic Geology, Austin, Texas 78713–8924
² Tately, N.V. and Associated Companies, Jakarta, 12190, Indonesia

Large volumes of CO2 occur naturally and are associated to varying degrees with economic methane accumulations, presenting significant economic exploration risks. While the association of CO2 and methane has been known for some time, exploration for and development of some of the worlds largest gas reservoirs on continental margins increasingly requires an understanding of the genesis, geologic controls, and subsurface processes involving associated CO2. In addition, the long-term development plans of identified but yet-unproduced methane accumulations span significant regulatory uncertainties related to the environmental liabilities of venting produced CO2. Such liabilities have resulted in recent non-regulated development decisions to include large-scale reinjection of produced CO2 (e.g., Sleipner & Snovit, North Sea; In Salah, Algeria, and Gorgon, northwest Australia). Reinjection of such large volumes of CO2 also requires an understanding of geologic controls of flow processes and permanent trapping (sequestration). One area of overlap of these two topics involves the geologic controls on CO2 and CH4 accumulation size. For field examples we are aware of in the GOM and SE Asia, structural compartmentalization appears to be a primary control of accumulation size. Charge rate (related to basin history) has also been considered, highlighting a major potential difference between natural accumulations and engineered re-injection volumes. We use a petroleum systems approach to investigate the stratigraphic and geographic distribution and association of natural CO2 and CH4 accumulations on continental margins. Summary statistics are provided to inform both risking of gas E&P projects, as well as feasibility of CO2 reinjection (sequestration) projects.

AAPG Search and Discovery Article #90158©2012 GCAGS and GC-SEPM 6nd Annual Convention, Austin, Texas, 21-24 October 2012