Chapter 5: Cold Enhanced Recovery

Many heavy- and viscous-oil reservoirs are either too thin or too deep for the application of steamdrives—gravity-drainage processes such as steam-assisted gravity drainage—or otherwise are not targets for air injection. Also, some of these formations may have underlying aquifers often referred to as bottomwater. According to US Geological Survey (USGS 2007), approximately 3 trillion bbl of heavy oil is at depths greater than 2,500 ft. Fig. 5.1 shows the distribution of deep heavy-oil basins around the world.

For such reservoirs, thermal methods may not be applied because of excessive wellbore heat loss, thin reservoirs (<12 m) that contribute to large reservoir heat losses, or steam scavenging by the bottomwater. As an example, steam loss (from wellbore heat loss) vs. depth for a typical heavy oil and a particular steam injection rate is shown in Fig. 5.2. At around 6,000 ft, 70% of energy is lost and it is only hot water that contacts the reservoir. Steam enthalpy is nearly constant up to 1,200 psi, and the constant enthalpy makes effective recovery of viscous oil easier.