Offshore Exploration Potential

ABSTRACT There are 799 indentified sedimentary provinces which possibly could contain hydrocarbons. Of these, 481 are located offshore or partly offshore. Eight of the 481 are considered to have excellent future hydrocarbon potential, 34 good-to-excellent, 42 good, 72 fair-to-good, 100 fair, 80 poor-to-fair, and 145 poor. There are numerous basins or provinces classification schemes attempting to equate type with hydrocarbon potential. The Bally and Snelson system and Klemme classification in current use indicate the most hydrocarbon-prone provinces are those formed on continental crust and associated with plate collision. The identification, location, classification and seriatim of offshore future hydrocarbon potential can be utilized by explorationists to screen those provinces having relatively poor hydrocarbon potential and those politically and environmentally unacceptable. The elimination of the objectionable provinces will enable the explorationists to concentrate on the high potential areas with acceptable parameters. INTRODUCTION There are 799 sedimentary provinces identified on the map, Sedimentary Provinces of the World (St. John, 1984). The term "provinces" includes basins, foldbelts, carbonate banks, cratonic arches, and deep sea fan and cone deposits of 1,000 meters or greater thickness. Of the provinces, 307 are located offshore, 174 are sited partly on and partly offshore, and 318 are onshore. Only those 481 provinces located offshore or partly offshore are considered in this report. Table 1. CLASSIFICATION There have been numerous attempts to classify sedimentary basins, or provinces, and to relate the various types to hydrocarbon potential. Two of the most frequently quoted systems are Bally and Snelson (1980), and Klemme (1971). Not all of 481 offshore provinces have been classified by Bally and Snelson or Klemme, whereas some have been assigned two classifications where there is superposition of types. Table 2. Numerically, the majority of sedimentary province considered offshore fall in Bally and Snelsons' genera types 1 and 3 and in Klemme's type III. However, a study of the location of known giant oil and gas fields (Carmolt and St. John, 1984), indicates the giants are found most commonly in provinces formed on continental crust and associated with plate collision. These are Bally and Snelson type 22, and Klemme type IIc. SERIATIM The 481 offshore sedimentary provinces are rated subjectively as to hydrocarbon potential. Political and environmental aspects are not considered. Table 4 The quality of hydrocarbon potential does not appear to be concentrated geographically but is distributed evenly worldwide. Table 5. The offshore sedimentary provinces having ranking from Excellent through Poor -to-Fair are presented in a seriatim of declining hydrocarbon potential for the top 337 provinces (Appendix). The 145 offshore provinces considered to have Poor potential were not ranked.