Abstract

Karachaganak field, brought on stream in 1985, is one of the largest accumulations of gas-condensate in the world. Located in the northern Pre-Caspian Basin (Kazakhstan), the field is a Permo-Carboniferous isolated carbonate platform, with a hydrocarbon column of about 1500 m.

The current development focuses the oil rim with gas injection in a confined area of the Platform Interior implemented since 2004. Among the future development scenarios under consideration, an increase of gas injection in different areas of the field was evaluated with the scope of maximizing liquid recovery and keeping the production plateau. The internal reservoir architecture is indeed very complex: an initial development of aggrading mounds is followed by prograding clinoforms passing to cyclic, grain-dominated platform interior sediments. The resulting reservoir quality is quite heterogeneous, with low porosity, but locally high productivity when affected by micro-fractures and vugs. The analysis was performed considering both incremental volumes of injected gas and the uncertainties affecting the reservoir to obtain a ranking which takes into account additional liquid recoveries and relevant risks. Eventually, the analysis led to a proxy function which, through a mean-variance optimization approach, was used to estimate the most favourable gas injection configurations, reaching the best compromise between recovery and uncertainty.

In conclusion, the analysis highlighted pros and cons for each reservoir area, offering a better view to optimize the future development. The depositional region where the injection was already implemented appears to be a good candidate; other areas, although affected by a certain degree of uncertainty, are also promising from the recovery point of view, while some other regions, characterized by high compartmentalization, seem to be less interesting.

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