Osmotic pressure is perceived as the cause of shale formation swelling during drilling. In the swelling process, low-salinity water enters the pores of shale, which swells the shale. Low-salinity water injected into high-salinity Bakken formation could similarly enter the matrix pores to displace oil by counter current flow, which we have observed in core experiments. As a result, we believe, low-salinity water can potentially enhance oil recovery from Bakken using appropriate injection-production well patterns. In this paper, we report on experimental and numerical modeling studies we have conducted to evaluate the potential of low-salinity waterflooding of Bakken. For laboratory experiments, we started with a vertical core obtained from a North Dakota, Middle Bakken primary horizon. Then, horizontal core plugs, parallel to the bedding plane, were drilled out from the vertical core for low-salinity experiments. In the mathematical model, we calculated osmotic pressure by tracking the salinity concentration. The model performance was calibrated against experimental results. In addition to osmotic pressure, gravity and capillary effects were also modeled. The results indicate that osmotic pressure promotes water-oil counter-current flow to produce oil from the shale pores. Oil production takes place not only in the water-wet rock but also in the oil-wet segments.
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