Computing Method Research On Sweep Efficiency Of Polymer Flooding For Five-Spot Pattern

At the oil fields, polymer flooding has been proved to be an effective EOR technology. Adding macromolecule polymer into water can increase the water viscosity and improve the mobility ratio, thus expand the sweep efficiency. What's a pity that there are a few scholars who had made research on the analytic calculation of sweep efficiency for polymer flooding by now. On the base of streamtube model of five-spot pattern, get a theoretical plate about the relation between sweep efficiency of polymer flooding and mobility ratio, which afford a theoretical criteria for compounding polymer viscosity at the oil fields.This thesis reviewed the development and states about the research method of sweep efficiency and stream tube at home and abroad. The main research methods about sweep efficiency are experiment, numerical simulation and empirical formula. The streamtube model has been built on the base of streamline and streamtube theory.Under the condition of homogeneous reservoir and constant injection rate, calculate the sweep efficiency for different mobility ratios by the streamtube model of five-spot pattern. When the mobility ratio is equal one, the sweep efficiency is 71% at the time of breaking of water flooding front. The error compared with the result of Muskat is only 1%. The changing trend under different mobility ratios is also the same as the experimental result. Calculated the curve indicated the time-dependence changing of flow rate and front location when the pressure drop is constant.By considering the absorbing factor and inaccessible pore, a linear dimension mathematic model of polymer flooding has been built on the base of mechanism of polymer flooding. We can get the changing regular pattern of sweep efficiency for different mobility ratios by solving the mathematic model in the streamtube model of five-spot pattern. Compiling this calculation process into the VBA software, we can draw the plate about the relation between the sweep efficiency and reciprocal mobility ratio under different water cut conditions. With the viscosity of polymer increased, the sweep efficiency also increased. It is indicated that the sweep efficiency of polymer flooding increased 5% than water flooding at the condition of the same water cut.Streamtube model of five-spot pattern has been built up for heterogeneous reservoir, compared the effect of heterogeneous reservoir on the sweep efficiency of water flooding and polymer flooding. The permeability of four stream tubes is 0.8D, 0.7D, 0.6D and 0.5D from inside to outside. The calculation indicates that the sweep efficiency for homogeneous reservoir decreased by 20% than the heterogeneous reservoir when the mobility ratio is equal one. However the sweep efficiency increased by 10% when the polymer was applied which indicates that polymer can expand the sweep area by adjusting the injection profile.