Reservoir Geology of the Karachaganak Field (Western Kazakhstan)

By

A. Giovannelli¹, M. Viaggi¹, S. Elliott², T. O'Hearn²

(1) ENI SpA-Agip Division, S. Donato Milanese (Milan), Italy (2) KIO Development Petroleum Engineering, Knightsbridge, London, United Kingdom

 Karachaganak Field in northwestern Kazakhstan is a giant gas condensate reservoir underlain by an oil rim with a compositional gradient from top to bottom. The Lower Permian to Upper Devonian carbonate reservoir contains 1.236 billion tonnes of liquids and 1.371 trillion cubic metres of gas in place (17.78 billion barrels of oil equivalent).

The Field is located at the northern margin of the Pre-Caspian Basin, a Palaeozoic rift basin that was active from the Devonian (or before) to the Early Carboniferous. The Hercynian compression inverted the structural regime in the Carboniferous and produced the thrust belts that currently border the basin to the East and South. The isolation of the basin from the Uralian Ocean was complete at the end of the Early Permian, resulting in the deposition of thick Kungurian evaporites.

The structure of the main reservoir is given by an isolated carbonate platform of Uppermost Devonian - Lower Permian age, the sealing is provided by the Kungurian evaporites. Upper to Lower Devonian series were also investigated by the drilling for exploration purposes.

The most complete pre-salt rock record in the basin occurs at Karachaganak, where the overall subsurface section ranges in age from Early Devonian (Emsian), through Early Permian (Artinskian). Due to its location, the sedimentary evolution of the Karachaganak reservoir was strongly controlled by Pre-Caspian geodynamics; its stratigraphic section therefore provides important insights for understanding the overall basin evolution.