By conventional mechanism, polymer flooding, due to its high viscosity, decreases the mobility ratio, increases the Volumetric Sweep Efficiency and recovery of the reservoir. When the fluid viscosity reaches a certain value, the decrease in mobility ratio has less effect on further increasing the volumetric sweep efficiency, therefore the practical amount and concentration of polymer that is used is limited.
However, due to the mechanism that the elastic properties of the driving fluid can increase the Displacement Efficiency, Daqing Oil Field started pilot tests of high elasticity driving fluid in the field 9 years ago, the incremental recoveries were all more than 20%OOIP above that of water flooding, about double that of conventional viscosity (40~50 cp) polymer flooding. Due to the very good results, in the recent 3 years, Daqing has rapidly expanded high viscous-elastic fluid flooding to more than 5 thousand wells. From the results of 1000 wells that are using this EOR method and for a sufficient time to predict the results, all these large scale field floods will attain an incremental recovery of more than 20%OOIP. Therefore, in Daqing, high elasticity flooding is taking the place of conventional polymer flooding and alkaline-surfactant-polymer (ASP) flooding to increase the oil field recovery.
Field experience shows the difficulties in solving the technical problems of producing, pumping, gathering and treating produced fluid from high viscous-elastic flooding are about the same as that of conventional polymer flooding and much easier to solve then ASP flooding.
The field results also show that the economics (costs per ton of produce oil) of this EOR method is about the same as conventional polymer flooding.
This is a very promising new EOR method that could significantly increase the recovery in other fields.