Brief Notes on the Structure of the Karachaganak Field, Kazakhstan

T. Birse¹, A. Francesconi², and Claudio Toscano². (1) Reservoir & Petroleum Engineering, KPO B.V, 2nd Floor, 4 Millbank, Westminster, London, England, (2) Exploration and Production Division, ENI S.p.A, Via Emilia 2, 20097 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 subsequent tectonic evolution;

• Devonian deposition in an extensional setting;

• Northward tilting, deposition of Upper Devonian and Carboniferous aged ramp platform 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-Serpukhovian section;

• Bashkirian deposition in the northern area of the field; • Deposition of Moscovian in an extensional setting;

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

• 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 Kungurian evaporites;

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

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