Water Shut-Off: Simulation and Laboratory Evaluation

Abstract

Abstract Many North Sea reservoirs are produced under waterflooding. With time the production wells start to experience water breakthrough problems due to incorformance of flood, gravity underride, presence of high permeable thief zones. The most common water shut off methods today are polymer gel treatment, cement squeeze and mechanical isolation. The polymer gel systems have several important advantages in comparison with other methods: – The polymer system is injected as a solution and can penetrate deep in the reservoir and reduce permeability in the near wellbore area. – The injected solution can move up and down the outside well bore, sealing cracks and existing microannuli especially in poorly cemented high permeable sands. – Gel left in the well bore can be cleaned out by jetting via coiled tubing with either a mild acid or water. – Not expensive due to reduced crew and rig time. During recent years polymer gel systems with Disproportional Permeability Reduction (DPR) effect were developed and successfully tested in the laboratories for North Sea reservoir conditions. Selective gels preferentially blocking water phase in the reservoir make well treatments more attractive, especially for advanced wells with complicated completion design (deviated, horizontal, multilateral). In spite of relatively small volume of chemicals involved in well treatments, evaluation of potential and possible benefits of near well treatments remain an important issue. Accurate near well model is required to simulate production of the well and effects of chemical treatment in the near well bore. Correct modelling of inflow is as important as representative modelling of gel generation process. Fine grid radial models allow to account more accurately for near well reservoir properties based on available log, core and production data. Template well models were established and used for screening of potential candidate wells for treatments. They proved to be useful in history matching and evaluating treatment effect in several field pilots in the North Sea. The paper will discuss the mechanism of water shut off, recent laboratory studies and screening results, give simulation and field evaluation examples for North Sea wells. P. 447