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Brief Notes on the Structure of the Karachaganak Field, Kazakhstan


Birse, T.1, A. Francesconi2, Claudio Toscano2 (1) KPO B.V., London, England (2) ENI S.p.A., San Donato Milanese, Italy


The Karachaganak Field is located at the northern margin of the Precaspian Basin. The field overlies a Devonian-Visean aged horst, upon which Upper Visean to Upper Serpukhovian carbonate platform lithologies have been deposited. Following a significant Carboniferous-Permian unconformity, Asselian to Artinskian pinnacle reefs grew. The sub­sequent deposition of the Filipov Anhydrite formation marked the onset of a period of evap­orite (Kungurian) deposition.

The reservoir section of the field can be sub-divided into six principle blocks, separated by a number of lineaments. These lineaments determined the subsequent tectonic evolution of the field.

The following sedimentary and tectonic events are evident:

            • Palaeozoic rifting which defined the lineaments that ultimately controlled subsequenttectonic evolution;

            • Devonian deposition in an extensional setting;

.           • Northward tilting, deposition of Upper Devonian and Carboniferous aged ramp plat-form sediments (Tournaisian to Bobrikovskian);

.           Tula deposition (middle to upper Visean) and southward tilting, probable indication of onset of Hercynian orogenesis in this area;

.           • Extensional and transtensional tectonics during the deposition of Visean-Serpukhoviansection;

.           • Bashkirian deposition in the northern area of the field; • Deposition of Moscovian in anextensional setting;

            • Possible uplift and inversion along pre-existing features in the central portion of thefield;

.           • Growth of Permian pinnacle reefs, principally overlying areas of tectonic inversion;

.           • Tectonic inversion in the western area (post-Filipov);

.           • Isolation of the Precaspian Basin from the Uralian Ocean, and deposition of Kungurianevaporites;

.           • Collapse of the Hercynian Orogeny (post-Kungurian – Triassic) and extension with pos­sible start-up of salt tectonics.