Heavy oil and bitumen reservoirs exhibit significant variation of oil composition and thus fluid properties, such as oil viscosity and density both vertically and laterally throughout the reservoirs 1. We believe this geo-intolerance, the excessive emissions and environmental impact, and consequent energy losses can be reduced and are due to insufficient tailoring of recovery processes to geological and fluid property variability commonly seen in heavy oil and bitumen reservoirs. Also, thermal processes produce large amounts of carbon dioxide emissions and use huge volumes of water. Also profit margins are small because of high capital and operational costs. The key problem of these processes is that they are not very geotolerant, that is, their performance is adversely affected by the reservoir geology and fluid heterogeneity. In situ processes to produce viscous and poor quality oils rely on high pressure primary production, as in cold heavy oil production, or thermal and/or solvent-based methods to mobilize the oil by reducing its viscosity. However, mining is only suitable for shallow resources, is very costly, and has high carbon dioxide emission and other environmental penalties. A recovery process such as mining is geotolerant, i.e., heterogeneity does not matter since all of the oil sand is processed and the oil recovery factor is high typically higher than 90%. The ideal process is one which is tolerant of heterogeneities, i.e., it is robust, has low environmental impact and high energy efficiency.įigure 1 displays the three axes that define a recovery process for oil sands: tolerance to geological and fluid heterogeneity (Geotolerance), environmental impact (gas emissions and water use), and energy efficiency. gSAGD is SAGD optimized for well placement based on the mobility distribution1.
SAGD and CSS have slightly better energy efficiency and emissions and water use but are not as tolerant to geological and fluid heterogeneities. Mining is tolerant to geological and fluid heterogeneities but has high emissions and water use and relatively low energy efficiency.
The three performance axes for thermal solvent oil sands recovery processes. We will show that the controlling variable on recovery of these resources is fluid compositional variations. Fluid heterogeneities refer to spatial variations of the fluid composition and properties such as viscosity and density. Geological heterogeneities refer to spatial variations of porosity, permeability, relative-permeability curves, shale and mud layers, etc. Two reasons account for this: first, geological heterogeneity in the form of variable rock and rock-fluid properties and second, fluid heterogeneities in the form of variable fluid composition. Average recoveries from heavy oil and oil sand reservoirs are typically low ranging from 5 to 15 percent for cold heavy oil production and from 30 to 85 percent for steam-based in situ processes.
The majority of the world’s petroleum resources are contained in heavy oil and oil sand reservoirs.
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