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Three basic stratigraphic problems, lithology, environment, and porosity, confront most geologists working with sedimentary rocks. An evaluation of any time or rock unit should involve all three problems with an economic focus on distribution of porosity--effective porosity. Conventionally, a complete evaluation would be accomplished by an integration of the conclusions of the separate problem analyses. A more desirable approach, prior to map interpretation, would be the integration of the basic data of these problems into an objective form, numerical units, common to each problem. With roots in a foundation of common measurement the solution to the separate analyses would be well coordinated and would result in greater accuracy with the integrated conclusions than that a hieved by compounding interpretations based on diverse units of measurement.
Lithoporosity is a technique which evaluates effective porosity by use of the lithologic factors which retard its development. These "retarding factors," derived from sample descriptions and other data, are given numerical values from a standard scale determined for the study unit. Such a derivation is part of a definite data synthesis to be followed. By this synthesis, preparation for a study must include exact correlations of the unit concerned and the establishment of certain standards for evaluation by lithoporosity. A tabulation of descriptive data in each well must then be made involving lithology, environment, fluids, and porosity from which retarding factors are to be estimated. Finally, specific data are extracted for map compilation.
By mapping retarding factors we obtain quality control and distribution of critical lithologic phenomena. With such control together with our mapping of other pertinent data from the tabulation we achieve an environmental concept of the unit. If we composite the retarding-factor maps and convert the resulting values to porosity equivalents we find that we have developed an areal distribution of effective porosity.
Utilizing standard subsurface information only, lithoporosity offers many advantages. Mainly, it can be used to evaluate single or multiple zones in any effectively porous sedimentary rock in situations where time and simplicity are of utmost importance. Above all, it is a complete synthesis intended to serve better the foremost geologic need--predictability.
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