Screening Criteria for Tertiary Processes

A large number of variables are associated with a given oil reservoir—for instance, pressure and temperature, crude oil type and viscosity, and the nature of the rock matrix and connate water. Because of these variables, not every type of tertiary process can be applied to every reservoir. An initial screening procedure would quickly eliminate some tertiary processes from consideration in particular reservoir applications. This screening procedure involves the analysis of both crude oil and reservoir properties. This section presents screening criteria for each of the general types of processes previously discussed in this except microbial flooding. (A discussion of MEOR screening criteria appears in section 11.3.5.3.) It should be recognized that these are only guidelines. If a particular reservoir-crude oil application appears to be on a borderline between two different processes, it may be necessary to consider both processes. Once the number of processes has been reduced to one or two, a detailed economic analysis should then be conducted.

Some general considerations can be discussed before the individual process screening criteria are presented. First, detailed geological study is usually desirable, since operators have found that unexpected reservoir heterogeneities have led to the failure of many tertiary field projects. Reservoirs that were found to be highly faulted or fractured typically yield poor recoveries from tertiary processes. Second, some general comments pertaining to economics can also be made. When an operator is considering tertiary oil recovery in particular applications, candidate reservoirs should contain sufficient recoverable oil and be large enough for the project to be potentially profitable. Also, deep reservoirs could involve large drilling and completion expenses if new wells are to be drilled.