Karachaganak Brownfield Vs. Kashagan Greenfield: Analogues Or
Authors: Albertini C. , Bado L. , Bigoni F. , Francesconi A. , Imagambetov K. , Leoni G. , Tarantini V. 
Published: March 2015

Can Karachaganak field, in production since 1984, represent a good analogue for Kashagan field which is approaching the production start-up? In fact the two carbonate buildups developed in the same geological context, the Pre-Caspian-Basin margins, during the same stratigraphic interval, Visean-Bashkirian.

While their depositional facies are comparable, their internal architecture, as inferred from seismic, is different. Karachaganak, affected in its early stage by tectonic, developed initially with aggrading mound complexes followed by prograding clinoforms; it is characterized by biohermal deposits passing, in its upper part, to cyclic, grain-dominated platform interior sediments. Kashagan started developing with a retrograding pattern followed by prograding and then aggrading patterns; it is characterized by a large platform interior, made of grain-dominated cyclic deposits, surrounded by a narrow biohermal rim and slope. The diagenetic overprint consists of marine cementation, dolomitization and later dissolution in Karachaganak while, in Kashagan, an early diagenesis, dominated by cyclic subaerial exposures and karst was followed by late burial cementation.

The resulting reservoir qualities reflect these different geological backgrounds. Karachaganak, quite heterogeneous, is dominated by microbial boundstone, in situ and breccias; it shows low porosity but locally high productivity when affected by micro-fractures and vugs. These characteristics are consistent with the wide range of well performances historically observed (orange!). Kashagan instead appears dominated by two rock types: platform cyclic grainy porous rock, having moderate productivity and cemented poor rim boundstones affected by outstanding productivity because of the presence of both karst and solution-enlarged fractures. These data support the expected bi-modal performances (apple!).

Introduction

Karachaganak field (KGK) is an onshore Kazakh field located in the northern area of the Pre-Caspian Basin. Discovered in 1979 and put in production in 1984, it represents one of the largest gas and condensate reservoirs in the world. Kashagan field (KSG) is an offshore Kazakh field located in the southern area of the Pre-Caspian Basin (Fig 1). Discovered in 1999 and put in production in 2013, it is considered one of the largest oil discoveries of the last 30 years.

These two giant fields consist of reservoir deposited during the same stratigraphic interval, Lower Carboniferous, in the same environment of deposition, carbonate ramp/platform, at just a distance of about 600 kilometers but at the opposite side of the same sedimentary basin.

The main difference between these two fields appears to be that while Karachaganak is a kind of brown field with an actual achieved RF of about 10% and large amount of geological/dynamic data endorsed during the long production history, Kashagan is a green field with a quite significant amount of geological data but no production history on which rely, definitely affected by a lot of uncertainties.

Therefore Karachaganak should represent a very good analogue of Kashagan, a very useful tool to interpret the geological data, to forecast the green field behaviour and to reduce the uncertainties.

This paper describes the comparison between the geological data of these two fields and the relevant interpretations, as per Eni's view, aimed to understand if they can really be considered as analogues.