ABSTRACT

Assessment of the relative merits of poorly explored regions can be made on the basis of a structural-sedimentological analysis of information from as few wells as one per region. The pertinent variables are (1) mean grain size, (2) sorting or clay content, (3) organic matter, and (4) rate of burial. This information is readily available from cores or samples, and reasonably good estimates can be made from modern log suites. For a "Most Attractive" rating, the possible reservoir beds in a well to be studied should have the mean size in the sand category, and sorting should be good-to-excellent (very little clay or fine silt); associated rocks should have a relatively high content of organic matter; and the indicated burial rate should be high.

A less satisfactory assessment, using these same concepts, can be made on the basis of general geological knowledge without well data. Under these circumstances, the required sedimentological information can be approximated from knowledge or inferences about climate and source lands at the pertinent time, and the rate of burial can be estimated on the basis of regional geological knowledge.

These techniques do not apply in dominantly carbonate or evaporite sections and hence cannot be used in the Florida and Yucatan areas. For the rest of the coastal plain and continental shelf of the Gulf of Mexico region, application of the four basic ideas indicates that the most attractive targets are in the states of Louisiana and Tabasco (and immediately adjacent areas), and that lesser production can be expected as one moves along the coast away from these prime targets. Hence North Tamaulipas, South Texas, and the Florida Panhandle should be less attractive targets, although nothing in the model indicates that they are barren.

Quick burial is commonly (but not invariably) associated with large river deltas. The deltas of the Grijalva-Usumacinta and Mississippi rivers meet this requirement. The delta of the Rio Grande, on the other hand, is not as attractive even though burial rates may have been high: the sedimentological data are not as encouraging as in Louisiana and Tabasco.