Selection And Evaluation Of Instant Polymer Displacement System In Offshore Oil Field

There exist characteristics of lower cementing strength, larger porosity, higher permeability, stronger heterogeneity, higher viscosity of crude oil, higher reservoir temperature and higher salinity of solvent water on Bohai oilfield. These characteristics result in worse development effect of water flooding. It is urgent to take measures as intensified fluid diversion to enlarge swept volume, thus improving the development of water flooding. In recent years, field tests about polymer flooding and polymer-gel flooding are conducted on SZ36-1 and LD10-1 oilfield, which attain obvious effect of increasing oil production and reducing water production. Such measures provide an effective way to enhance oil recovery efficiency on offshore oilfields. Compared with oilfields on land, space on the offshore platforms is smaller, which put forward higher request of allocation and injection equipment of polymer and the dissolution rate of polymer. According to the actual demand of polymer flooding on offshore oilfields, the issue, based on the reservoir geology characteristic and fluid property of Bohai oilfield, theoretically guided by reservoir engineering, physical chemistry and macro-molecular chemistry, by means of instrumental analysis, chemical analysis and physical simulation, regarding viscosifying ability, salt resistance, thermal stabilization, rheology, viscoelasticity, seepage characteristic, flooding efficiency and flooding effect as evaluation index, carried out the optimization of soluble polymer, property appraisal of polymer-gel system and technology design of injection equipment. Results showed that soluble polymer which was labeled as Polymer 2 had better comprehensive property. The polymer-gel system that was composed with Polymer 2 and 2# organic Cr3+, not only owned better property of salt resistance, but also performed unique seepage characteristic that the residual resistance factor was bigger than resistance factor. Compared with polymer solution, the flooding injection of Cr3+ polymer-gel system was higher, and the effect of enlarging swept volume was better. The composition of polymer-gel system was: Polymer 2 was chosen as the polymer with the concentration of 1500mg/L~2500mg/L, 2# organic Cr3+ was chosen as the cross-linking agent, the “polymer: Cr3+=120:1~270:1, and the slug size was 0.10PV~0.20 PV.