Terms
The volumetric sweep efficiency at any time is the fraction of the total reservoir volume contacted by the injected fluid during the recovery. When using water, consideration of the mobility of the fluids, is an important factor when determining the area and vertical sweep efficiencies. This would help to determine the mobility ratio. If M is less than 1 then oil is capable of travelling at a rate equivalent to the water. An increase in the viscosity of the oil would mean that M would increase and this would lead to the injected fluid moving around the oil. This would also make it harder for the oil to penetrate the pore. To improve this ratio then the viscosity of the water has to be increased. When M is greater than 1 the displacing fluid has greater mobility than the displaced fluid. Also the position of the water injection and the flooding patterns would go a long way to determining the recovery patterns. Also to consider in oil recovery is the position and orientation of the injection wells around the production well. As the mobility ratio increases the sweep efficiency decreases. Once a channel of water exists between the injector and the producer then little additional oil would be recovered.
If permeability varies vertically then an irregular vertical fluid front can develop and this is as a result of the differing permeabilities and the mobility ratio.
Displacement efficiency refers to the fraction of oil that is swept from unit volume of reservoir upon injection. This depends on the mobility ratio, the wettability of the rock and the pore geometry. The wettability is determined by whether or not the grains preferentially absorb oil of water.
Read more about this topic: Enhanced Oil Recovery
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