Study on Blockage and Fluid Diversion Behaviors of Polymer Microspheres

Abstract

Polymer microsphere (PM) flooding is a deep fluid diversion technology that is suitable for high water-cut oilfields to further enhance oil recovery. It has been successfully applied in some oilfields in China. However, the flow characteristics of polymer microspheres in porous media are very complex, involving blockage, elastic deformation, and remigration. On this account, we used microfluidic tests and core flow experiments to investigate how polymer microspheres block pore throats and promote fluid diversion. Two types of microfluidic chips are first used to study the flow behaviors of polymer microspheres at the pore scale. The blockage and migration behaviors are observed through a single microchannel, and the real-time inlet pressure is monitored by a precision pressure sensor. To explore how polymer microspheres divert fluid, the unequal-diameter dual microchannel model tests are carried out. On this basis, the capacity of polymer microspheres to adjust the shunt flow in high and low permeable cores was investigated by a parallel sand-packed pipe flow experiment from a macroscopic level. The results of the single microchannel model tests show that when the particle size of the polymer microspheres is smaller than the inner diameter of the microchannel, the microspheres can freely pass through the microchannel. When the particle size of the microspheres is larger than the inner diameter of the microchannel, the microspheres may first be blocked in the microchannel, and then deform and migrate through the microchannel; correspondingly, the inlet pressure first increases and then decreases. When multiple large-sized microspheres are bridging and blocking the microchannel, it may be difficult for the microspheres to enter and pass through the microchannel, and the inlet pressure shows a rising trend. The results of dual microchannel model tests show that the polymer microspheres can divert flow direction by alternately blocking wide and narrow microchannels. The results of the parallel sand-packed pipe shunt flow experiment show that the polymer microspheres can cause fluid diversion by blocking high permeable cores so that more subsequent fluid can enter the low permeable cores. The variation of the shunt flow rates in the two sand-packed pipes directly reflects the fluid diversion capacity of polymer microspheres from a macro perspective. Polymer microspheres flooding breaks the shackles of the traditional idea of using homogeneous displacing fluid to increase oil recovery. As a novel aspect, this paper further interprets how polymer microspheres block pore throats and promote fluid diversion, which is the key mechanism for enhanced oil recovery of this heterogeneous particle suspension.