An Overview of 1-D Biodegradation Modeling for Pre-Drill Prediction of Oil Quality

Marcano, Norka¹; Larter, Steve; and Bennett, Barry
¹[email protected]

The relationship between heterogeneous petroleum composition in heavy oilfields and petroleum biodegradation caused by biological action in reservoirs has been qualitatively well known for many decades. Oil biodegradation adversely impacts oil quality, with major economic consequences as most of the world’s petroleum is biodegraded. The details of the organisms, the spatial relationships between the anaerobic, biological, physical and chemical processes involved and the timescales of in reservoir petroleum biodegradation have, however, remained mysterious until the last decade or so (Head et al, 2003). Pre-drilling prediction of biodegraded petroleum fluid properties remains one of the major challenges in petroleum exploration and appraisal. In this presentation we review some of the published 1-D methods proposed for assessing or modeling the risk of finding biodegraded oil and predicting oil or gas properties. In general, the reservoir temperature history and oil mixing are the primary controls on oil biodegradation (Larter et. al, 2003, 2006; Adams, 2008; Adams et al, 2013), although several other processes also play a role. The effects of biodegradation are predictable using key controls such as reservoir temperatures, oil charge/spill rate, reservoir geometry, water leg extent and oil composition. The integration of key processes of biodegradation with dynamic basin evolution and reservoir properties is best accomplished by using numerical models. In this work we review the published state of the art in process background for achieving effective numerical modeling of in-reservoir biodegradation. We also present some case histories to demonstrate how these processes impact compositional and fluid property gradients (API gravity and viscosity) in extra-heavy oil accumulations, focusing on the settings seen in S. America, especially those in foreland basins, and how these in turn impact recovery processes. We demonstrate, using the 1-D approach, as described in detail in Larter et al (2006), the application of biodegradation modeling for pre-drilling prediction of oil property trends, looking at the impact of petroleum systems components, specifically charge and reservoir burial history, on the oil fluid property evolution in typical reservoirs. We will describe and present summary model types for the typical trap types and basin styles found in key S. American petroleum systems and basins.

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