Rejuvenate High WCT Horizontal Wells in a Complex Carbonate Reservoir: A Case Study

B oilfield in the Middle East is a complex carbonate reservoir with strong vertical heterogeneity, regional distribution of high permeability streak and locally developed fracture area. In order to enhance oil recovery from reservoir management point of view linear well pattern with horizontal producers at top of the reservoir and injectors at bottom of the reservoir was adopted for development with water flooding. The existing high permeability streak was not fully recognized at the beginning of the drilling stage for limited well counts before the commencement of water flooding so for some horizontal wells 7 inch production casing was run above the high permeability streak and this made the high permeability streak exposed to the production interval and this results in water breakthrough along the high permeability streak from the injectors to the producers. Rapid water cut increase was noticed after short time of tie-in and the high water cut accelerate the deployment of ESP for stabilizing oil production. Well trajectories are close to or partially penetrated into the high permeability streak and communication between injector and producers is established through local fracture account for few producers with unexpected high water cut so it is not the priority of discussion in this paper. The rapid water break through short time after the water flooding started and this greatly weaken the overall water flooding effect and cause high water cut issues at low recovery factor of OOIP either for individual producer or even the whole reservoir. In order to address the high water cut issue of producers with high water cut resulted from high permeability streak as the dominating channel for water break through three cases are designed and they are respectively re-completion with NICD, AICD and side track. The three cases are designed and simulated with Netool and the optimized design parameter are incorporated into the reservoir model with history match done for forecast for performance evaluation through comparison with the base case. The work flow for the optimization of case design and simulation is also established. The simulation results indicate that both the re-completion with either NICD or AICD and side track contribute to decreasing of the water cut as the production continues and improve final recovery. Re-completion with NICD maximum decrease water cut by 19.1% with average of 1.17% until the end of the contract for 98.98Mstb incremental oil, re-completion with AICD maximum decrease water cut by 17.6% with average of 2.56% with validity period of 6.9 years for 132.59Mstb incremental oil and sidetrack decrease water cut by 22.9% with average of 4.01% with validity period of 6.8 years for 203.32 Mstb incremental oil. The effect of re-completion with AICD is superior to that of re-completion with NICD as to re-completion and sidetrack comes at the top of the choices discussed for total oil.