Most of the largest oil and gas fields of the world produce from structural traps, but some very large fields and many smaller ones are stratigraphically entrapped. Most of the large stratigraphic fields have been found by non-technical methods, or accidentally. Geophysical techniques have been successful in finding reefs but much less so with wedgeouts of porous stratified rocks. The best method for finding the latter is careful geological work coordinated with geophysical surveys, and drilling of wells. Except for reefs, the proportion of stratigraphic fields eventually to be found probably will not be greatly different from the present ratio.
Le plupart des plus grands champs de pétrole et de gas du monde sont productifs dans des pièges structuraux, mais quelques trés grands champs et beaucoup des plus petits sont piègés stratigraphiquement. Le plupart des grands champs stratigraphiques ont été trouvés par methodes non-techniques, ou par hazard.
Les techniques géophysiques ont abouti à des succès en trouvant des recifs, mais beaucoup moins en ce qui concerne les biseaux de roches poreuses stratifiées.
La meilleure méthode de recherche pour le second type est l'étude géologique detaillé coordonnée avec des levées géophysiques et le forage de nombreux puits. Sauf dans le cas des recifs, le pourcentage de champs stratigraphiques suceptibles d'être eventuellement découverts dans l'avenir ne sera probablement pas beaucoup different de la proportion actuelle.
Few stratigraphic type fields are localised without relationship to the structure of the enclosing rocks. In By a broad definition, stratigraphic type oil and gas a broad sense they are related to the tectonic framefields are those in which a reservoir rock is laterally work of the sedimentary basin in which they occur, terminated or reduced in permeability to the extent that and its development before, during, and subsequent to escape of hydrocarbons up the regional dip has been the deposition of the lenticular reservoir rock. In a prevented, the reduction in reservoir quality being the narrower sense, the stratigraphic variations which are principal cause of entrapment of oil and gas. ubiquitous in sedimentary rocks affect reservoirs on Stratigraphic traps may be classified in the following anticlines as well as on broad homoclines, and cross groups: warps on otherwise evenly dipping strata commonly determine the area of a wedging clastic layer which is impermeable facies. among geologists as to whether certain fields are
2. Permeable reservoir rock truncated by an un- primarily the result of stratigraphic or structural conformity and sealed by an impermeable over- factors. Levorsen' recognised a separate category of lapping stratum.
