Design of Geotailored Recovery Processes to Produce Oil Sand Reservoirs
Ian D. Gates1, Steve Larter2, and Jennifer Adams2
1Chemical and Petroleum Engineering University of Calgary
2Geology and Geophysics University of Calgary
There are two basic requirements that all thermal heavy oil or bitumen recovery process must achieve: first, mobilize the oil in the reservoir, and second, move the mobilized oil to a production well. In thermal processes, the first requirement is achieved by heating the oil. In current thermal oil sand recovery processes such as Cyclic Steam Stimulation (CSS) and Steam-Assisted Gravity Drainage (SAGD), mobilized oil is moved to the production well by one or more of the major drive mechanisms: formation recompaction, solution gas drive, and gravity drainage. In CSS, in early cycles, recompaction and solution gas dominate. In later cycles, gravity drainage grows more important. In SAGD, gravity drainage is the dominant recovery mechanism. Oil mobility, the controlling factor for flow of oil in reservoirs, is heterogeneous in oil sand reservoirs and can vary by up to a couple orders of magnitude spatially in these types of reservoirs. Given the more narrow variability of permeability, oil mobility heterogeneity can be dominated by oil viscosity heterogeneity. The oil phase viscosity is controlled by the oil composition whose variation in vertical and lateral directions originates from the balance between fresh oil charge, biodegradation, mixing of fresh oil with biodegraded oil, component diffusion, and transport of nutrients within the reservoir over geologic timescales. The viscosity distribution is also influenced by the burial history of the reservoir as well as porosity, permeability, and pore size distributions of migration pathways and the reservoir. It has been shown that vertical and lateral viscosity variations significantly affect current recovery processes such as CSS and SAGD. However, recovery processes can be designed, that is geotailored, to be more tolerant or even take advantage of fluid viscosity heterogeneities. One example of this is the J-well and Gravity Assisted Steam Stimulation (JAGASS) process. In this work, geotailored recovery process design including operating strategy, well placement, and cold, thermal, and thermal-solvent sequencing will be discussed. These geotailored processes are likely to outperform current processes such as CSS and SAGD.
AAPG Search and Discovery Article #90075©2008 AAPG Hedberg Conference, Banff, Alberta, Canada