New Insights about Processes and Products of Reservoir Charge, Entrapment and Biodegradation with Implications to Heavy Oil Reservoir Developments – Principles and Examples from Canada and Elsewhere

Fustic, Milovan¹; Bennett, Barry; Oldenburg, Thomas; Huang, Haiping; and Larter, Steve
¹[email protected]

The Athabasca Oil Sands Deposit, one of the world’s largest petroleum accumulations, contains an estimated 1.7 trillion barrels of heavily to severely biodegraded oil with API gravities ranging from 6 to 10.

Recent qualitative and quantitative analysis of bitumen molecular composition (biomarkers) within the detailed sedimentological framework on both reservoir and basin scale provided new insights about petroleum system. Data clearly shows strong evidence of inter-compartmental petroleum 'fill and spill' charge and entrapment and that bitumen compositional and viscosity variations are due to different level of biodegradation. Additionally, our interpretation of the interplay through time and space of depositional setting and anaerobic biodegradation suggests that top water and other highly water-saturated zones are related to the formation and the subsequent depletion of gas caps, likely derived from microbial gas generation that followed petroleum entrapment.

Implications to heavy oil reservoir developments are significant. We suggest that integrated baseline studies of sedimentological and geochemical variation interpretation allow for (1) mapping and (2) prediction away from well control of the extent of top gas, top water and high-water – low-bitumen saturated zones, as well as bitumen properties variations throughout the reservoir. Geochemical data from integrated baseline studies is a powerful tool for identifying lateral compartments and barriers or baffles to vertical fluid communication, while they may also be applied towards production optimization and allocating production along horizontal wells including the assessment of steam chamber growth in oil sands operations.

Comparison with data from many heavy oil fields hosted in similar geological settings demonstrates that developed principles are universal.

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013