Karachaganak is a giant oil, gas and condensate field located in north-western Kazakhstan, operated by Karachaganak Petroleum Operating b.v. (KPO b.v.). 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 consist of gas-condensate and oil with strong compositional gradients.
Since 1997, the focus of the field development has been on the oil rim with the objective of producing low GOR oil. This is being achieved by drilling sub-horizontal wells. The design of these wells is aimed at maximizing the reservoir contact to overcome the challenges of significant heterogeneity present in the field. It also allows to access to partially or fully isolated compartments associated with both reservoir heterogeneity and the presence of clinoforms formed during the evolution of Carboniferous platform.
Initially horizontal wells were completed open-hole. Since 2011 new horizontal wells start being completed with multi-stage stimulation completions (swelling packers and sliding sleeves). Previous attempts at analyzing the benefit of multi-stage stimulation were hampered by a small population size for meaningful statistics. Today, the number of wells completed with multi-stage completions with available data is over 50. It's now therefore possible to make firmer conclusions regarding the potential benefits of multi-stage completions.
Three specific areas of potential benefits of multi-stage completions over open holes have been identified and reviewed, these are as follows: Impact on well PI – Initial well PI (Deliverability);Flow Distribution – Percentage of wellbore contributing to flow (Enhanced sweep efficiency), andEase of well re-entry for rig-less operations – Data acquisition and remedial jobs.
The available data indicate that multi-stage stimulations improve well productivity, downhole flow profile and the number of zones that contribute to flow. In addition to these primary benefits, there is an improvement in the ability to intervene in wells for data gathering. Based on these findings, it can be concluded that multi-stage completions result in a net positive contribution.
