Polymer Flooding Cluster Residual Oil And Its Microscopic Oil Displacement Law

Cluster-type residual oil accounts for a huge proportion in all types of residual oil, but the correlative research work of cluster-type residual oil is seldom and most of the work is carried out on the micromodel whose pore structure is extremely similar to reservoir. So it is weak targeted and poor experimental reproducibility for researching cluster-type residual oil. In addition, there is short of systemic and quantitative research on the micro displacement of cluster-type residual oil as well as its influence factors. Therefore, this work present a combination of experiments including the establishment of the setup of micromodel displacement, the determination of oil displacement system, the formation of cluster-type residual oil after water flooding, polymer flooding and its influence factors to investigate microscopic displacement law of cluster-type residual oil. It is benefit for the development of cluster-type residual oil in reservoir and the screening of displacing fluid. The main contents are as follows:First of all, according to the pore structure of the cluster-type residual oil in the reservoir, 8 kinds of micro-visual models, which have a unique pore structure— "small pores surrounded by big pores", were designed for researching the cluster-type residual oil specially, including 4 kinds of micromodel with the same small pore width(8?m) but the different pore diameter ratio(3 times,5 times,8 times and 10 times) and 4 kinds of micromodel with the same pore diameter ratio(5 times) with the different small pore size(8?m?12?m?16?m? 20?m). On the basis, the micro-chips which fulfill the requirement of visualization were fabricated after screening the transparent materials and surveying the existing processing technology. And finally, the setup of micromodel displacement was assembled with the micro-chip, the micro syringe pump (minimum flow 2nL/min), the real-time pressure acquisition system and the real-time video acquisition system.Secondly, calculate the shear rate of polymer flowing in porous media on the basis of the permeability of micromodel measured by the Darcy law and the Darcy velocity determined by the critical viscoelastic velocity. The glycerin, HPAM and hydrophobically associating polymer CP-1 which have the same shear viscosity that are separately 10mPa·s,30mPa·s, 50mPa·s at 30.7s-1 were determined by the shear rate scanning test on advanced rheometer. At the same time, the first normal stress difference of oil displacement system was tested.Thirdly, the morphology of residual oil after water flooding and the effect of displacement velocity and pore structure on water flooding were studied by utilizing the setup of micromodel displacement. The study found that after water flooding, the oil recovery of high permeability zone is up to more than 70% and the residual oil is dispersion-type. In the middle and low permeability zone, the oil recovery is less than 5% so that there is residual oil which almost fill in all small pores. When the water flooding velocity is higher (6m/d), it is easy to break the structure of the cluster-type residual oil. When the water flooding velocity is higher (0.8m/d), there is a wide of residual oil in high permeability zone.3m/d was selected as water flooding velocity. The change of pore structure parameters of micromodel has little effect on water flooding.At last, the experiment temperature is 45?. Polymer flooding the cluster-type residual oil and its influence factors was studied. The study found that polymer go along with one or several channels which have lower resistance into the low permeability zone and then divergently move forward to expand swept volume and push the cluster-type residual oil out. When the displacing front of polymer breakthrough, the residual oil that still stuck in the micromodel will be difficult to activate, the oil recovery of cluster-type residual oil is increasing with displacement velocity and the main reason is the increase of the displacement pressure synchronously. When the viscosity of oil displacement system increases, the oil recovery of cluster-type residual oil is surge. When the shear viscosity of displacement system is the same, the greater of the elasticity is, the greater effective viscosity and the displacement pressure are, the higher oil recovery is. fixed the small pore width or pore diameter ratio, when the pore diameter ratio increases, the oil recovery will decrease. When small pore width increases, the oil recovery will increase. So there is a critical pore diameter ratio (or small pore width). When pore diameter ratio (or small pore width) is greater than (or smaller than) the critical value, the oil recovery will be close to zero. With the increase of oil viscosity, the oil recovery sharply decrease. By comparing the change rate of influence factors with one unit increment of oil recovery, it's found that the influence factors with the degree of influence on oil recovery from large to small are oil viscosity, oil displacement system viscosity, displacement pressure, the first normal stress difference, displacement velocity.