南阳油田驱油用聚合物的水动力学半径研究

RESEARCH ON HYDRODYNAMIC RADIUS OF POLYMER MOLECULE FOR OIL DISPLACEMENT IN NANYANG OILFIELD

为了获得聚合物分子尺寸与油藏孔喉配伍性的关系,采用动态光散射(DLS)技术测定了南阳油田聚合物驱使用的多种聚合物分子的水动力学半径(Rh).根据'架桥'原理,当聚合物分子水动力学半径大于0.46倍孔喉半径后可对多孔介质形成堵塞.南阳油田聚合物驱油藏的平均孔喉半径中值分布为4～16 μm.驱油用聚丙烯酰胺产品的Rh分布有3种类型:其一是Rh分布较集中,尺寸过大的分子少,不易堵塞地层;其二为含有微凝胶杂质,Rh分布宽,大尺寸分子多,易堵塞地层;其三为分子量虽低,但分布宽,且集中在两端,结果是低分子量部分增黏能力差,高分子量部分易堵塞地层.试验表明,南阳油田在聚合物驱中,聚合物产品品质差或用清水配制聚合物溶液,又遇到油藏渗透率较低时易发生堵塞.

In order to study the compatibility of polymer molecular size with porous throat in reservoir,hydrodynamic radius(R_h) of several kinds of polyacrylamide(HPAM) used in polymer flooding in Nanyang Oilfield was measured with dynamic light scattering(DLS).According to the 'bridging' principle,the relationship of hydrodynamic radius(R_h) of the polymer molecule can form stable block to the pore throat and radius of the pore throat(R) would be: R_h≥0.46R.Generally,median of average radius of the pore throat(R) in most zones varied from 4 μm to 16 μm in polymer flooding,Henan Oilfield.There were three types of R_h distribution for HPAM products used in oil displacement.Firstly,the R_h distribution of HPAM was quite centralized and it was difficult for this kind of HPAM with few big size polyacrylamide molecules to block formation.Secondly,the R_h was very wide and big size molecules and a lot of impurity(microgel) could easily block formation.Thirdly,although molecular weight of HPAM was low,the R_h distribution was still wide with two distribution peaks located at two ends.As a result,the thickening ability of those polymer molecules with ultra-low molecular weight was too low,and the others with high molecular weight could block the formation.Therefore,formation block would appear if the quality of polymer product was low,or polymer solution was prepared with fresh water when polymer flooding was applied in the reservoirs with low permeability.