Effect of Wettability and Fractures System on Oil Recovery in a Naturally Fractured Reservoir

From three-dimensional water saturation development during water floods at water wet and at oil wet conditions in un fractured and fractured blocks of chalk, Water movement during water flooding was significantly affected by the presence of fractures at strongly water-wet conditions and at oil wet conditions. For un fractured and embedded fractured chalk the oil recovery by water flooding was similar for water-wet chalk and for oil wet chalk, if the fractures permeability after fracturing was high enough with compare to matrix permeability the oil recovery was similar for embedded fractured and interconnected fractured chalk. Production rate and total oil production was affected by fractures at water-wet and oil wet conditions. For oil-wet chalk oil recovery was reduced when the permeability increase after fracturing was high. Open fractures are a key to produce water gravity segregation, when water enter an open fracture it accumulate at the bottom of fracture and makes gravity segregation. The recovery mechanisms changed towards more viscous dominant flow regimes at less water- wet conditions; this was even observed in fractured blocks. At interconnected fracture network, the vertical fractures which have not role in the transfer of water from inlet to outlet, act like weak barriers against the flow .After their behind blocks were filled with water they act like a closed fracture. At oil wet conditions they act like a fracture forever. Increasing the flow rate has been shown to produce a less dispersed waterfront. In water floods starting at higher initial water saturation there was essentially no water front at all, i.e. a uniform increase in water saturation was recorded. Water breakthrough in the block with interconnected fractures occurred somewhat earlier and the block produced slightly less oil. The hydraulic contact from inlet to outlet also resulted in a period with two-phase production. This trend is more noticeable for the higher permeability increase with connected fractures. In the water wet system if there is a hydraulic contact between inlet and outlet (interconnected fracture system) there is an increase in recovery compare to conventional reservoir or an embedded fracture system and in an oil wet system the presence of fractures itself is good enough to ensure a higher oil recovery compare to a conventional reservoir and the type of fractures (embedded or interconnected) has not an efficient role in changing the recovery. At the end, there is a comparing between simulation runs and experimental jobs which had been done by graue et.al. to validate the accuracy of simulation jobs.

Keywords:

Wettability , Fracture system , Naturally Fractured reservoir , Simulation , Oil recovery