Most of the old oilfields in eastern China have already entered into an ultrahigh water cut period, but their annual oil production and remaining recoverable reserves still occupy a pivotal position. Due to severe edge-bottom water coning, the main horizontal production well G104-5P70 of Gaol04-5 block in Jidong oilfield has seen an early water breakthrough while a large amount of remaining oil is still stuck in the high structural region. An innovative in-depth fluid diversion technique, gel barrier placement (GBP), proves to be a promising approach to tap the potential of remaining oil in the period of ultrahigh water cut, which involves injecting gel into the horizontal well at the toe end to form 'gel barriers', then the edge-bottom water will bypass these barriers and be diverted into the upper zones where the remaining oil is relatively enriched. In this present work, sensitivity analysis was carried out to study the influence of plugging location, plugging size and plugging strength on the in-depth fluid diversion effect, and optimization design of the plugging system was then conducted with regard to the agent dosage and slug combination. Simulation results indicate that: (1) the main plugging location should be the upper two layers while the appropriate angle between gel barrier and horizontal wellbore is 45°; (2) an obvious water plugging effect is observed for gel barriers with radial slug length of 80m, horizontal probing thickness of 10m and vertical plugging ratio of 0.6; (3) with the permeability reduction factor around 0.05, gel barrier placement will ensure a comparatively high enhanced oil recovery; (4) three-round injection mode is designed to apply on 1500m3 compound plugging agent for the gel barrier placement. Field application shows mat the designed GBP is valid for two years with increased oil amount of 1670t and enhanced oil recovery of 6.4％. Compared with traditional profile control techniques, gel barrier placement has prolonged the water control period, improved the plugging accuracy and reduced the plugging agent dosage. It will provide an effective reference for similar edge-bottom water reservoirs in ultrahigh water cut period to further enhance oil recovery.
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