In reservoirs with certain dip, the steam chamber advances different than in conventional SAGD projects. Since the horizontal permeability is normally higher than vertical permeability and because reservoir pressure is lower toward up-dip; an early lateral growth of the steam chamber should be promoted to the uppermost reservoir position. If horizontal permeability controls the gravity drainage instead of vertical permeability, it is thought that a good gravity drainage process in dipped reservoirs could be achieved, even in cases were vertical transmissibility is poor. However, if there is mobile water within the reservoir, then the steam easily flows up-dip and away from the producer well diminishing the hot oil draining to the producer and affecting the SAGD well's performance.
The factors affecting SAGD efficiency in a dipped-bed extra heavy oil reservoir (6.5°API) located in southern llanos Colombia have been analyzed. An important extra heavy oil accumulation toward the outcrop of main production sands was encountered. The reservoir temperature is low (100°F) so bitumen viscosity is high (>100.000cp). In addition, oil saturation could be lower than is the standard for commercial projects in some areas.
A reservoir characterization was done using data from 18 wells. Information from basic and special logs, routine and special core analyses as well as displacement tests was used to build a robust numerical model. Several numerical simulations were run to address the performance of SAGD under such conditions. Particularly, the amount of mobile water and dip, play a major role in SAGD efficiency since the steam chamber behaves accordingly to both parameters. Numerical simulations done in this work have shown that SAGD thermal efficiency in dipped bed reservoirs is dramatically affected by energy losses toward the uppermost reservoir position since the steam tends to flow up dip far from producer wells. This effect is amplified when mobile water is within the porous medium.
Different strategies to improve SAGD efficiency were explored by numerical simulation. Well configuration was changed from parallel to staggered; electromagnetic heating was evaluated as well as hybrid processes. Hybrid processes could certainly open doors for economic development of highly viscous heavy oil reservoirs with mobile water saturation.