Water Flooding, CO_2 Flooding and Water-alternating-CO_2 Flooding Effect Contrast in Extra-low Permeability Reservoir

To extra-low permeability reservoirs,we simulate the practical reservoir conditions and carry out water flooding,CO2 flooding and water-alternating-CO2 flooding in laboratory.The results show that under the same conditions the recovery of water alternating-CO2 flooding is 22.63 percent higher than that of CO2 flooding,and 27.22 percent higher than that of water flooding.For water flooding,the water breakthrough time is early,moisture content rises fast,and injection pressure is high.Although CO2 flooding injection pressure is low,CO2 gas channeling is very serious.The injection pressure of water-alternating-CO2 flooding is higher than CO2 flooding,but far lower than the water flooding pressure.The gas breakthrough time and water breakthrough time of water-alternating-CO2 flooding is separately later than CO2 flooding and water flooding,but gas-oil ratio and moisture content rise slowly.Therefore,when using CO2 flooding we should first choose water-alternating-CO2 flooding.