Abstract: Oil Prospects in Gulf of Mexico Region

William F. Tanner

Assessment of the relative merits of poorly explored regions can be made on the basis of a structural-sedimentologic analysis of information from as few 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 geologic knowledge, without well data. Under these circumstances, the required sedimentologic information can be approximated from knowledge about climate and source lands, and the rate of burial can be estimated on the basis of regional geologic knowledge.

These techniques do not apply in dominantly carbonate or evaporite sections, and hence cannot be used, as stated, in the Florida and Yucatan area. 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 directly 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 there is nothing in the model to indicate that they are barren.

Quick burial commonly (but not invariably) is 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 so attractive, even though burial rates may have been high: the sedimentologic data are not so encouraging as in Louisiana and Tabasco.

AAPG Search and Discovery Article #90975©1976 GCAGS- GC Section SEPM Annual Meeting Shreveport, Louisiana