Experimental Research On Enhancing Oil Recovery In Fractured Reservoir By Increasing Energy With Osmotic Pressure

Typically, the recovery of fractured hydrocarbon reservoirs is very low. In order to enhance the oil recovery of fractured reservoir, this paper is aimed at providing a method of enhancing the oil recovery of fractured reservoir(especially those in low pressure and low energy) by increasing energy with osmotic pressure. The principle of this method is to use osmosis membrane materials on the basis of water driving, then osmosis membrane can be formed on the surface of matrix, as a result, the injected water can permeate into the matrix automatically with the action of osmotic pressure. In addition, the energy of matrix can be enhanced, the trapped oil can be drained, then the process of self-imbibition-energy enhancement-oil drained can be realized. This thesis adopts copper sulfate and potassium ferrocyanide to analog the two-fluid process, then a semi-permeable copper hexacyanoferrate membrane can be formed. In the experiments, I’ll evaluate the effect of osmotic pressure from the following five aspects: the component concentration( 0.12mol/L, 0.24mol/L, 0.36mol/L, 0.48mol/L, 0.60mol/L), the temperature(40℃, 50℃, 60℃, 70℃, 80℃), the salinity(20000mg/L, 40000mg/L, 50000 mg/L, 60000mg/L, 80000mg/L, 100000mg/L), the pH value(pH=3~11) and the permeability of core(0.8μm2~2.3μm2). The result shows that the influence factors of osmotic pressure will obey the following patterns while improve the oil recovery. Firstly, when the concentration of semi-permeable membranes, the ambient temperature and the salinity increase, the recovery degree will increase; secondly, when the pH value is partial to low or high, the recovery degree will decrease; thirdly, when the permeability of reservoir increases, the recovery degree will decrease. Meanwhile, the feasibility and the principle of this method will be elaborated in the thesis. The osmotic pressure can enhance the energy mainly because the low salinity water in fractured reservoir could penetrate into the matrix through the semi-permeable membrane under the action of osmotic pressure. As a result, the energy of matrix can be enhanced, the trapped oil can be drained. The results of feasibility study shows that the osmotic pressure can really help to drain oil and enhance the oil recovery, but at the same time it depends on the salinity of the reservoir and the integrity of a certain semi-permeable membrane. The main reason why osmotic pressure can enhance oil recovery by increasing energy is that the water which is unable to flow into the fractured reservoir matrix before can permeate into the matrix under the action of osmotic pressure, then the swept area can be enlarged.