The results of lab tests show that an incremental recovery over water flooding of more than 20% OOIP (original oil in place) can be obtained by early time injection of high molecular weight, high concentration polymer solutions, and the earlier the better. The incremental recovery is comparable to surfactant flooding but at a lower cost.
After the success of a pilot test injecting high concentration polymer fluids in Daqing Oil Field, a high concentration (concentration 1,500 ppm ~ 2,000 ppm, viscosity 400 mPa.S ~ 500 mPa.S) polymer flood pilot test has been started in May 2003. The purpose is to (1) study the feasibility of high concentration polymer flooding, (2) provide technical and practical experiences for expanding this technique to other areas of Daqing Oil Field. The pilot is located in the West Central area of Daqing Oil Field and consists of 9 injectors and 16 producers. Before high concentration polymer flooding, 0.247 pore volumes of low concentration (1,000 ppm, viscosity 44mPa.S~51 mPa.S) polymer solution had been injected and the water cut at the central area had reached its lowest point (65.5%). By the end of Dec. 2005, the water cut at the central area was 79.1%. After injecting high concentration polymer solution, the rate of the water cut increase slowed down and then the water cut decreased from a maximum of 79.6% to a minimum of 73.1% (a decrease of 7.5%) again. The current daily oil production is 29.5 tons. The daily oil production increased from a minimum of 29.8 tons to a maximum of 40.5 tons (an increase of 35.9%). The current recovery over that of water flooding is already 14.3% OOIP. According to numerical simulation, when the water cut reaches 98%, 19.8%~22.9% OOIP incremental recovery over that of water flooding will be attained.
Recently, 6 dispersed wells located in the West Central area of Daqing Oil Field started to inject a higher concentration of polymer fluid also. The 6 wells were first stimulated and then increased the concentration of the injected polymer solution from 1,000ppm to 1,300ppm. At present, good results have been obtained.
The above results illustrate that the injection of high concentration polymer fluids in the field is feasible and can further enhanced the oil recovery significantly. Very few fields have injected such high concentrations of polymer fluids; it should be of reference value to the design and implementation of future chemical (especially polymer) floods.