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.