CONTINUOUS-TYPE (UNCONVENTIONAL) ACCUMULATIONS


     Continuous-type (unconventional) accumulations are, for the purposes 
of this assessment, defined to include those oil and gas resources that
exist as geographically extensive accumulations that generally lack well-defined 
oil/water or gas/water contacts (fig. 5). This geologically grounded definition 
provides a set of consistent criteria to be applied in the determination of 
whether a specific accumulation is or is not conventional. This geologic definition 
intentionally avoids the regulatory criteria of the Federal Energy Regulatory 
Commission (FERC) designations and does not rely on any specific permeability as 
a defining criterion. Included in this category are coal-bed gas, gas in many of 
the so-called "tight sandstone "reservoirs, and auto-sourced oil- and gas-shale 
reservoirs.  Because of the immense quantities of oil and gas that can be included 
in this category, only those resources that, in our judgment, are technically 
recoverable and could be added to U.S. oil and gas reserves were reported in this 
study. Those resources judged to be potential additions to reserves are further 
subdivided into undiscovered and reserve growth categories. Existing technology and 
development practices as of the date of this assessment (January 1994) were assumed. 
In this study, inferred reserves and undiscovered resources in continuous-type 
accumulations were not differentiated.  Therefore, the volumes of resources estimated 
for continuous-type deposits occur over both the hachured and stippled areas of the McKelvey 
box (fig. 4).

     Each of the three broad categories of resources (undiscovered conventional 
accumulations, inferred reserves, and continuous-type accumulations) requires a
different technique for evaluation. Each of these resources is thus described and 
considered in separate sections of this report. The methods for assessment of the 
undiscovered recoverable discrete conventional accumulations is discussed further in 
the CD-ROM chapter on methodology by Gautier and Dolton (Gautier and others, 1995). 
The techniques used for evaluation of various continuous-type resources are discussed 
in CD-ROM chapters by Schmoker and by Rice (Gautier and others, 1995). Results of the 
assessment of these various resources are generally reported in separate categories.