Abstract

Diapirs, usually composed of evaporites but also formed from shale or serpentine, occur in all parts of the world except the shield areas. They are particularly prevalent along passive continental margins. They are the locus of hydrocarbon accumulations which have been found around the Gulf of Mexico, in Germany, the North Sea, Russia and elsewhere. Most diapirs grow as a result of forces which are essentially due to sediment loading, assisted by the relative buoyancy of the diapiric material. Examples from the Gulf Coast of North America illustrate the growth histories of salt diapirs, and the occurrence of hydrocarbons related to them.

Diapirs create and modify local hydrocarbon traps. Regional stratigraphic analysis is essential to predicting the depth and occurrence of potential reservoirs and source beds. Diapir-associated traps are divided into three basic groups as they relate to depth of objective reservoirs:

1. Piercement — objective reservoirs penetrated by diapiric material.

2. Non-piercement — objective reservoirs occur above the diapiric material.

3. “Turtle” — objective reservoirs formed into anticline created by movement of salt into adjacent diapirs.

Each of the basic groups is usually modified by faulting and/or stratigraphic changes, which in many instances are directly related to the growth of the diapir.