Fire flooding process has been applied to the thick and deep heavy oil reservoirs G3618 and G3 in Liaohe oil field in China. Currently, there are two main operating issues: the serious combustion front gravity override, and the low areal sweep efficiency. Thus, research of process control is conducted for the entire project area, each layer, and also individual well patterns, with the objective of achieving better vertical and areal conformance.
G3 and G3618 have average thickness of 68.6m and 103.8m, with similar depth of 1600m. Three major process control methods are used: using vertical-horizontal well configuration, reconfiguring to line drive plus vertical-horizontal hybrid configuration, and air injecting at top positions. We establish geological model with focus on interlayer vertical communications. Through reservoir simulation and field data analysis, we test potential benefits of using horizontal producers. We further compare the different performances of line drive and pattern flood in G3618 and G3. Finally, with G3618 having 20 degree dip angle, we test the effect of air injection at higher elevations through simulations and laboratory experiments.
First, we have found 2m as the critical thickness for shale interlayer barriers to prevent vertical communications and to minimize gravity override. The combination of vertical and horizontal wells shows great improvements in conformance, since the horizontal producer at bottom of the reservoir could more effectively drain the reservoir. Second, we find line drive is more effective than pattern flood with recovery improvement of around 10%, proven by reservoir simulations and field production analysis. Third, if we inject from top, we benefit from high recovery of gravity drainage, with much oil accumulated at reservoir bottom. We recommend conducting top injection when reservoir thickness is above the critical value of 20m. Finally, we have establish line drive fire flooding configuration in G3 reservoir with air injectors located at top positions of the reservoir, which causes oil production rate to increase by about 80% since initiating these adjustments. For G3618 reservoir, we have also reconfigured the well patterns to line drive with air injectors at elevated locations, with daily production rate increased by 30%.
Through field experience, we have found that controlling combustion front override and improving areal sweep efficiency are great technical challenges for fire flooding process. We demonstrate that measures of implementing line drive, injecting at the top while producing at deeper locations, and configuration of vertical injectors and horizontal producers have already made significant improvements in fire flooding production performance in Liaohe oil field in China.