ABSTRACT
Richfield East Dome Unit (REDU) is located in Orange County, California, southeast of Los Angeles. The East Dome Unit contains several massive unconsolidated sand zones which were produced by depletion drive from 1920 to 1974. In 1974, a water-flood was initiated in the Chapman Zone. The performance of the waterflood has been reduced by the highly hetergeneous nature of the Chapman sand and by the adverse water-oil mobility ratio resulting from the high viscosity crude oil present. Preliminary evaluation of various enhanced recovery processes indicated that the application of mobility control polymer, coupled with selective permeability variation control treatment of certain injection wells, could improve the oil recovery efficiency of the waterflood.
Extensive laboratory testing was conducted in Chapman cores and sand packs to select the most applicable mobility control polymer and the most effective permeability variation control process.
Five commercially available mobility control polyacrylamide polymers were screened to determine their suitability to REDU reservoir rock and fluids. Selection criteria included the oil recovery efficiency, polymer retention, polymer solution viscosity, and residual resistance factor. As a result of the laboratory tests, Cyanatrol WF-940S was selected for additional field testing.
Three commercially available polymer permeability variation control processes were also evaluated in the laboratory. The ability of each process to improve the dimensionless flow rate ratio in parallel sand pack tests was used as the main selection criterion. A polyacrylamide treatment utilizing aluminum cross-linking was selected for additional field testing.
Field tests of both the mobility control polymer and the permeability variation control polymer process have been initiated in the Chapman Zone of the Richfield East Dome Unit.
