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Abstract
The majority of the world’s petroleum resources are contained in heavy oil and oil sand reservoirs. 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. There are two reasons for this: first, geological heterogeneity in the form of variable porosity and permeability properties and secondly, fluid heterogeneities in the form of variable saturations, fluid compositions and thus viscosity. Geological heterogeneities refer to spatial variations of porosity, permeability, relativepermeability curves, shale and mud layers, etc. Fluid heterogeneities refer to spatial variations of the fluid composition and properties such as viscosity and density. Given that the permeability often varies by less than an order of magnitude whereas the oil viscosity varies by up to two orders of magnitude in a bitumen reservoir, the controlling variable on recovery of these resources is often fluid compositional variations. Due to the large viscosity contrast between oil and water at native reservoir conditions water is often the most mobile phase within a bitumen reservoir. This research identifies preconditioning techniques that can be used to alter reservoir or fluid (oil or water) properties prior to thermal recovery reducing adverse reservoir factors and improving recovery, environmental impact and process economics. We describe here a simulation study of one application related to modifying the variation of oil viscosity in the reservoir prior to steam injection. The methods make use of mobile water within the reservoir, to distribute viscosity-reducing agents before steam injection, and represent another means of geotailoring recovery processes to the features of the reservoir. The main benefit is that recovery process performance, both in terms of oil production rate and thermal efficiency, is improved.

Introduction
Figure 1 displays the three factors that provide a measure an oil sands recovery process: tolerance to geological and fluid heterogeneity (geotolerance), environmental impact (greenhouse and acid gas emissions and water use), and energy efficiency. A recovery process such as mining is geotolerant, i.e., geological heterogeneity does not matter since all of the oil sand is processed and the oil recovery factor is high typically higher than 90%. However, mining is only suitable for shallow resources, is very costly, and has high carbon dioxide emission, water usage and tailings pond issues incurring environmental penalties. 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. The key failure of these processes is that they are not very geotolerant, that is, their performance is adversely affected by the reservoir geology(e.g. shale) and fluid heterogeneity. Also profit margins are small because of high capital and operational costs. Also, thermal processes produce large amounts of carbon dioxide emissions and use huge volumes of water. We believe this geo-intolerance, the excessive emissions and environmental impact, and consequent energy losses can be reduced and are commonly due to insufficient tailoring of recovery processes to the geological and fluid property variability commonly seen in individual heavy oil and bitumen reservoirs.