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Experimental Investigation of Immiscible N2 WAG in Saline Reservoir at Ultra-High Water-Cut Stage
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, IOR 2019 – 20th European Symposium on Improved Oil Recovery, Apr 2019, Volume 2019, p.1 - 11
Abstract
Gas enhanced oil recovery (EOR) has shown notable improvement in the saline reservoir after water flood. Nevertheless, gas channeling often occurs resulting in poor sweep volume and inefficient oil displacement. Water-Alternating-Gas (WAG) injection is recommended as improving gas mobility control. Herein, a series of coreflood tests were done to investigate the potential of continues gas injection (CGI) and WAG injection at ultrahigh water cut stage in the saline reservoir. The mechanisms of immiscible N2 WAG injection on residual oil distribution (ROD) was analyzed combined with the pore-scale analyzation. Also, the effect of injection parameters on ROD and recovery efficiency were evaluated.
Core-flood results show that tertiary oil recovery efficiency resulting from WAG injection is significantly high than CGI at the ultra-high water cut period. Pore-scale visualization results show that gas moves through the waterflooded channels into the pore space occupied by previously water and residue oil, then become a trapped gas. Injected gas can reduce residue oil saturation whereby displaced/collected residual oil into large waterfilled pores and blocked some water channels. WAG flooding can decrease free gas saturation and increase trapped gas saturation significantly, resulting in decreasing gas and water relative permeabilities. The experiment of optimization result indicates that proper design parameters of WAG could contribute 15.62% OOIP recovery, where is injection pore volume (W+G) of each cycle of 0.3PV and injection gas/water ratio on 2:1. In this study, we explain the mechanism of immiscible N2 EOR at the ultra-high water cut reservoir, the results of injection parameter effect can help researchers and reservoir engineers better understand and implement the immiscible N2 EOR method in the saline reservoir. The achievements of this study are also the foundation of the saline reservoir at ultra-high water cut stage improved remaining oil sweeping efficiency and enhanced oil recovery.