Study of Polymer Flooding in Heterogeneous Porous Media by Using Nuclear Magnetic Resonance

摘要

Polymer has been successfully used to enhance crude oil recovery at high water cut stage. However, the application of polymer flooding is limited by the heterogeneity of reservoir. In this work, the role of polymer flooding in heterogeneous reservoir was explored by nuclear magnetic resonance (NMR) spectroscopy. Parallel core displacement experiments were carried out to study polymer flooding in heterogeneous formation. The results showed that the polymer flooding area was related to permeability and pore connectivity. At the end of the water flooding stage, the residual oil was not evenly distributed in porous media. The percent crude oil recovery increased with the increase of pore diameter. Crude oil recovery from cores with larger pores was higher, and water broke through the highly permeable core first. After 0.3 PV polymer injection, the water mobility of the high permeability core decreased. Polymer injection showed a dual effect, an oil displacement effect and a traction effect. The oil displacement effect was responsible for driving out the crude oil in large pores, whereas the traction effect was responsible for driving out residual oil from small pores. After 1 PV polymer injection, the polymer solution channeled through the highly permeable core rapidly. The crude oil in large pores was washed out completely. The NMR water-phase spectrum line of the highly permeable core was much higher than that of the low permeable core. Under different core permeability and porosity, the NMR peak of the crude oil-phase spectrum line indicated that the polymer flooding is mainly effective on pores ＞ 40 μm.