Heavy Oil-the final frontier! Practical basin- and reservoir-scale simulation of biodegradation using 1 to 3D models to effectively predict reservoir fluid properties

Jennifer Adams¹, Christopher Neufeld², Dan Carruthers², and Steve Larter^1
1PRG, Univ. of Calgary, Calgary, Alberta, Canada
²Permedia, Ottawa, Canada

Heavy oils and tar sand massively dominate the world oil inventory with heavy oil production increasing worldwide. Risking the chances of finding viscous non-economic heavy oils in deep water prospects is crucial for exploration decision making today. Heavy oil and tar sands are formed by microbial degradation of conventional crude oils over geological timescales and the Bacchus consortium at the Universities of Calgary (Canada) and Newcastle (UK) has defined and quantitated the key mechanisms of heavy oil formation(1-3). Constraints such as oil charge rate and charge mixing, reservoir temperature-dependant biodegradation rate and water and nutrient supply to the organisms ultimately dictate the final distribution of API gravity and viscosity found in heavy oil fields(2,3). Large-scale lateral and small-scale vertical variations in fluid properties due to interaction of biodegradation and charge mixing are common, with up to orders of magnitude variation in in-reservoir viscosity over the thickness of a reservoir in super heavy oilfields. These variations in fluid properties ultimately control the production character of these heavy oil fields and the ability to pre-drill predict fluid properties is a core element in exploration decision making for reservoirs that are shallow enough and cool enough for biodegradation to alter the oil quality. Equally prediction of fluid properties between well control is key to optimizing production from these heterogeneous accumulations.

The Permedia Research Group and Bacchus have been working closely to couple Permedia’s high resolution 4D modeling software with the science base from Bacchus II. The product is a 3D fluid property prediction tool that effectively integrates the dynamics of active oil charging with biological degradation of oil in reservoirs across individual accumulations or for whole basins. This substantial technical challenge has been met and the new MPath tool (“BaccPath”) can effectively predict API gravity and viscosity for accumulations through time and space. A 1D interrogation tool (“Gnawd”) allows users to develop detailed models of individual reservoir segments and estimate vertical compositional gradients related to biodegradation. With the world’s oil supply increasingly moving towards heavy oil supply and with biodegradation risk a key component of most active oil exploration areas of the world today, the new Permedia-Bacchus tool effectively brings the dominant processes acting on most of the world’s oil to the modeling armory of today’s basin modeling community. We describe the approach and conclude that direct determination of oil charge rate to prospects remains the major outstanding challenge of basin modeling in that this is the key parameter controlling not just level of degradation and fluid properties, but prospectivity in general. We discuss solutions to direct charge rate determination in basin models.

1. Head, I.M., Jones, D.M. and Larter, S.R.(2003) Biological activity in the deep subsurface and the origin of heavy oil. Nature, 426, 344-352.
2. Adams, J., C. Riediger, M. Fowler, and S. Larter, 2006, Thermal controls on biodegradation around the Peace River tar sands: Paleo-pasteurization to the west: Journal Of Geochemical Exploration, v. 89, p. 1-4.
3. Larter, S., H. Huang, J. Adams, B. Bennett, O. Jokanola, T. Oldenburg, M. Jones, I. Head, C. Riediger, and M. Fowler, 2006, The controls on the composition of biodegraded oils in the deep subsurface: Part II - Geological controls on subsurface biodegradation fluxes and constraints on reservoir-fluid property prediction: AAPG Bulletin, v. 90, p. 921-938.

 

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