Abstract

There is a substantial difference in understanding structural style and in exploration when rifting is viewed in three dimensions rather than by using 2-D visualization.

Examples of the differences are illustrated in AAPG Memoir 46 (1989) entitled “Extensional Tectonics...of the North Atlantic...” Here both symmetrical and asymmetrical “rift” basins are discussed, and the productive potential of each is vastly different. Asymmetrical basins are more abundant; symmetrical basins produce most of the hydrocarbons and are thence suitable exploration objectives. True rifting, caused by thermal uplift, has to be modeled in 3-D to be understood. The combination of increasing heat flow and dilational tectonics provides the ideal set of conditions for maturing and entrapping the hydrocarbons, and these conditions are found only in symmetrical rift basins.

Extensional asymmetric basins have different thermal histories, and do not offer comparable advantages. Thus, to call both types of basins rifts is misleading. This has resulted from the use of planar models, which suggests that extension in all directions (dilation) is mechanically similar to extension. That is true only with planar models and not in the real world.

In addition to entrapping oil and gas more efficiently, rifting associated with thermal uplift creates symmetrical traps that are far easier to locate. Furthermore, subsequent cooling and collapse of thermal uplifts drops many traps into what now appears to be inferior structural positions. Thus, half of the fields in the Permian Basin remain to be fully exploited, and that should also be true for other rift basins.