Cimmerian Structures Imaged on Modern 3-D Seismic Data in the North Caspian Fold-and-Thrust Belt of Kazakhstan

Kosi, Walter ¹; Schmitz, Joerg ¹; Tari, Gabor ¹; Tikhonov, Vladimir ²
(1)OMV, Vienna, Austria. (2) Petrom Kazakhstan, Aktau, Kazakhstan.

The North Caspian Fold and Thrust Belt of Kazakhstan lies between the Precaspian Basin to the north and the Mangyshlak Palaeo-Trough to the south. The undeveloped Kultuk Field onshore is located along the frontal zone of this folded belt, very close to the Caspian coastline. Less than ideal vintage 2D seismic and well data defined the traps for the Kultuk field as low-amplitude structural closures within the Middle Jurassic. However, a newly acquired 225 km² 3D seismic data set provided not only a better understanding of the trap configuration within the known reservoir interval, but it also imaged, for the first time, the deeper structure beneath the field.

Based on the integration of the 3D seismic data with existing well data, the intra-Jurassic closures are interpreted as reactivated four-way closures above prominent north-vergent Cimmerian anticlines. These anticlines are arranged in an en échelon pattern in a broad E-W trend, just like the well-known Buzachi Fold and Thrust Belt to the W from the Kultuk Field. The age of the anticlines is latest Triassic (hence the designation as Cimmerian) as the Jurassic could be mapped as clearly onlapping these compressional structures, especially on their southern back limb. The detachment level for the thin-skinned anticlines appears to be within the Upper Paleozoic, close to Carboniferous/Permian boundary. Whereas most of the anticlines are controlled by a single north-vergent thrust fault, in a few cases the 3D seismic data revealed there are significant south-vergent back-thrusts. Also, there are major oblique normal faults present with a trend of NE-SW. These trends are inherited from earlier deformational episodes.

The recognition of prominent Cimmerian anticlines beneath the Kultuk Field has important implications for exploration as deeper play types may exist in the Triassic, Permian and Carboniferous strata.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.