Research and Application of Micron-Size Polyacrylamide Elastic Microspheres (MPEMs) as a Smart Sweep Improvement and Profile Modification Agent

摘要

Micron-size polyacrylamide elastic microspheres (MPEMs) are a smart sweep improvement and profile modification agent, which can be prepared controllably through inverse suspension polymerization using acrylamide cross-linked with an organic cross-linker. MPEMs can tolerate high temperature of 90 °C, high salinity of 20000 mg/L and wide pH value range of 4.0-10.3. MPEMs can suspend in produced water easily and be pumped into formation at any rate. More importantly, MPEMs can reach the designed size after hydration swelling in formation and a reliable blockage can be formed; MPEMs can deform elastically and move forward step by step to realize a moveable sweep improvement and profile modification process in reservoirs. In this paper, the pore-scale visualization experiments were conducted, and the results indicate that MPEMs prefer to enter into large pores, and can selectively plug large pore-throats through mechanisms of capture-plugging, superposition-plugging and bridge-plugging; the plugging at inlet is temporary, and MPEMs can deform depending on their elasticity and pass through these pore-throats through four steps of capture-plugging, elastic deformation, steady migration and deformation recovery. Heterogeneous double-tube physical modeling experiments under the simulated reservoir conditions show that MPEMs mainly enter into and plug high permeability layer whose permeability is reduced from 3.642 μm~2 to 0.546 μm~2 , and almost do not clog low-permeability layer whose permeability is reduced from 0.534 μm~2 to 0.512 μm~2 ; the enhanced oil recovery (EOR) mainly comes from the low-permeability layer (15.49% from low-permeability layer compared with 4.37% from high-permeability layer) and total EOR is more than 12%. Field application results of MPEMs treatment in a serious heterogeneous, high temperature and high salinity reservoir show that MPEMs can effectively improve swept volume and displacement efficiency. Because of the excellent properties, MPEMs treatment will become a cost-effective method for sweep improvement and profile modification to serious heterogeneous, high temperature and high salinity reservoirs with fractures and channels.