Fracture has a significant impact on sweep efficiency of displacement agent, especially for WAG process. Flooding can be affected negatively by the formation of water and gas channeling. Numerical efforts have been made to improve WAG in fracture reservoirs, however, some deficiencies still exist in understanding behavior of plugging agent and designing injection strategy. This study is conducted to investigate mechanisms of polymer gel injection for profile modification during WAG in fractured reservoirs by core flooding tests and numerical model simulations. Additionally, effect of gel solution on improving sweep efficiency under different WAG parameters is evaluated.

Cores with artificial fractures are applied to flooding experiments using oil, water, CO2 and polymer gel solution. CT image analysis is conducted to evaluate the effect of fracture, WAG and gel injection parameters on performances of sweep efficiency during WAG process. Results of core flooding are matched with numerical simulation model to optimize scheme of gel solution injection.

Core flooding experiments indicate that polymer gel solution in proper composition can control displacement profile effectively by observing CT scan images that can evaluate oil distribution changes quantitatively by image analysis. Additionally, injection strategy of gel profile modification for oil recovery in the period of WAG is optimized by using the core-scale model matched with core flooding, mainly including gel injection volume and timing. Relationship between fracture and injection strategy of WAG and gel is also analyzed. It is shown that WAG ratio of 1:1, small WAG single slug, large volume of gel and early gel injection can provide favorable condition for EOR in reservoir with large fracture. However, considering issues of economy and injection pressure, too large and early gel injection would affect oil production negatively.

The purpose of this study is to provide a much more in-depth and comprehensive understanding of polymer gel control for fractured reservoir during WAG. The idea of method can be an effective guide for enhancing field oil production.

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