Screening Criteria

Table 11.2 contains the screening criteria that have been compiled from the literature for the miscible, chemical, and thermal techniques.

Table 11.2 Screening Criteria for Tertiary Oil Recovery Processes

The miscible process requirements are characterized by a low-viscosity crude oil and a thin reservoir. A low-viscosity oil will usually contain enough of the intermediate-range components for the multicontact miscible process to be established. The requirement of a thin reservoir reduces the possibility that gravity override will occur and yields a more even sweep efficiency.

In general, the chemical processes require reservoir temperatures of less than 200°F, a sandstone reservoir, and enough permeability to allow sufficient injectivity. The chemical processes will work on oils that are more viscous than what the miscible processes require, but the oils cannot be so viscous that adverse mobility ratios are encountered. Limitations are set on temperature and rock type so that chemical consumption can be controlled to reasonable values. High temperatures will degrade most of the chemicals that are currently being used in the industry.

In applying the thermal methods, it is critical to have a large oil saturation. This is especially pertinent to the steamflooding process, because some of the produced oil will be used on the surface as the source of fuel to fire the steam generators. In the combustion process, crude oil is used as fuel to compress the airstream on the surface. The reservoir should be of significant thickness in order to minimize heat loss to the surroundings.