LAPOINTE, PHILIPPE A.
Kharyaga, located in the Komi Republic (CIS), is a multi-pay oil bearing field. The Late Devonian carbonates of Object 2 form one of the most interesting of the targets. While drilling, several wells reported heavy mud losses, sometimes total, tool breaks and drops of several meters. The recoveries of cores cut in those wells were generally poor, and large vugs and abundance of fractures were present.
A detailed examination of these cores reveals the karstic nature of these features: conduits passing to large cavities, caves with network distribution, fissures enlarged by leaching, morphologies with erosion overprint, karstic breccia, local filling with green shales, geodic sparite cement, true speleothems. All these karstic features were confirmed in thin sections. Some bitumen is locally associated with the karstic levels.
The karstified zone shows a large vertical and horizontal distribution. The karst appears polycyclic, one of the latest phases remains open. Overall porosity is increased and permeability drastically improved. The tested wells in this zone have a very good productivity index. Other sector shows breccia related to paleokarst, their reservoir characteristics are still attractive if compared to the non karsted zones. The mapping of the karsted reservoir is based on all the data collected (mud-logging, electrical-logging, cores and production data). This mapping is a critical factor for reservoir management and field development.