Using CO₃ Decompositional Kinetic Parameters to Model the Generation and Expulsion of CO₂ in the Malay Basin, Malaysia

Azlina Anuar and M Jamaal Hoesni
PETRONAS Research and Technology Division, Malaysia

Carbon isotope data indicate that the CO₂ encountered in the Malay Basin originated from both organic and inorganic origins. In this study, the potential inorganic sources for CO₂ in the Malay Basin are investigated. Amongst the possible origins of the inorganic CO₂ are the thermal breakdown of calcareous shales and limestones as well as the diagenetic siliciclastic reactions whereby carbonate minerals such as siderite, dolomite and calcite in clastic sediments react with silicates at temperatures greater than 320°C to generate CO₂.

Decompositional kinetic parameters were determined for the Lower Oligocene calcareous shale and limestone samples from the Malay Basin. These specific carbonate decomposition kinetics are then used in 1D basin modeling to assess the timing of CO₂generation and expulsion. Having detailed kinetics data benefit the modeling by providing better control and, thus, more reliable results of the CO₂generation and expulsion as they are explicitly for the Malay Basin. In addition, temperature modeling within the Malay Basin was undertaken and this, in turn, allows the prediction of CO₂generation from diagenetic reactions within the penetrated sediments by determining the time when the critical temperature of 320°C was reached.

Using the newly-acquired kinetic parameters, we were able for the first time to determine the timing of inorganic CO₂generation and expulsion as well as its most likely inorganic origin in three (3) areas of the basin. To ascertain the trapping feasibility of the generated CO₂, the resulting timings were compared with the thermal subsidence and basin inversion of the Malay Basin. In summary, CO₂generation on the northeastern flank of the Malay Basin, which occurred at 2Ma, essentially came from the breakdown of the limestones. The central Malay Basin, on the other hand, received contributions from the breakdown of limestone and calcareous shale between 20Ma and 21Ma, and from siliciclastic reactions at 14Ma. The CO₂in the southern part of the Malay Basin was generated by the limestones and was modeled to expel at 14 Ma ago.

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands