Several papers on polymer flooding pilot test in Daqing have been published previously, they stress on enhancing oil recovery by polymer flooding in thick pay zone of major reservoirs with high permeability and heterogeneity. This paper presents the polymer flooding pilot test results in thin layers of non-essential reservoirs with medium-low permeability and heterogeneity. The purpose is to:

  1. study the feasibility of polymer flooding in such thin pay zones;

  2. test separate injection techniques;

  3. provide data for further extending polymer flooding potentials.

The pilot has 4 injectors and 9 producers in inverted five spot patterns. The polymer flooding through Putaohua P I 1–3 formation had been finished in this pilot in 1990, then S II 10–16 was plugged and S II 10–16 was perforated to perform polymer flooding by dual-pipe separate injection. S II 10–16 formation includes 5 sedimentary time units and has complex geometry of sandbody and some layers pinch out in a few wells in the pilot. Its microstructure relief is large, the deference in depth of the formation is 3 7 meters. The net thickness of a single layer is 0.4 to 4.0 meters. Its average permeability is 0.342 m2 and Dykstra-Parson coefficient is 0.6. Polymer injection started in December of 1993 and 0.35 PV of polymer solution has been injected by the end of 1995.

When 0.025 PV polymer solution was injected, the producers responded one after another. The average water cut of the pilot decreased from 94.5% to 80.1% and daily oil production increased from 37 tons to 95 tons maximum. The water cut of the central well decreased from 95.1% to 63.1%, daily oil production increased from 8 tons to 33 tons. Up to now the oil recovery for the central well has increased 10.84% OOIP over water flooding with the polymer flooding efficiency of 151 tons of oil per ton of polymer.

The measurements of injection and production profile showed that the heterogeneity of the reservoir is adjusted and that separate injection technique by dual-pipe is feasible.

P. 431

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