Karachaganak is a giant gas-condensate field located in north-western Kazakhstan. In 1997 a production sharing agreement was signed between the partner companies and the Republic of Kazakhstan. Karachaganak Petroleum Operating b.v. (KPO b.v.) joint venture is operated by Shell (previously BG-Group) and Eni S.p.A. Chevron, LUKoil and KazMunayGas are the rest shareholders in this project. Karachaganak was discovered in 1979 and the production began in 1984. The field comprises Permian and Carboniferous reservoirs with complex geological and fluid properties. The reservoir fluids are gas-condensate with the underlying oil leg. Since 1997 the focus of the field development has been on the oil leg with the objective of producing low gas-oil ratio (GOR) oil. This is being achieved by drilling sub-horizontal wells. The design of these wells is aimed at maximising the reservoir contact to overcome the challenges of significant heterogeneity present in the field. It also allows accessing partially or fully isolated compartments associated both with reservoir heterogeneity and with the presence of clinoforms formed during the prograding phase of the Carboniferous platform evolution. Initially a drain length of sub-horizontal wells was limited to 700 metres by the available drilling technology. Today, modern rigs are capable of drilling a single 2000 metre long sub-horizontal drain to a total well length of more than 6600 metres. Simulation studies indicate that long drains optimise the field development by reducing the number of wells required to maximise the oil recovery. This paper focuses on the impact that drilling long sub-horizontal wells has had on well performance in the Karachaganak field. The paper also discusses the evolution of the well completions from open-hole drains to multistage stimulation completions that allow selective stimulation of a drain interval.

No abstract