Experimental Study On Enhancement Of Thick Zone Recovery Efficiency By Adaptive System After Polymer Flooding In Daqing Oilfield

The typical problem in Daqing oilfield after years of polymer drive development is that the inhomogeneity of thick reservoirs is further aggravated,the distribution of remaining oil is more fragmented,and the dominant seepage channels are obviously developed,which requires a combination of plugging and adjustment to further improve the recovery of inhomogeneous reservoirs.Therefore,pre-cross-linked gel particles(PPG)are combined with the ternary system to form an adaptive oil drive system.The two play a synergistic role in blocking the high permeability layer and the dominant seepage channel,and at the same time,the subsequent injection of the adaptive system causes deep fluid flow diversion,which expands the wave volume of the middle and low permeability layers,thus improving the recovery rate after polydrive.In this paper,a porous permeable long core model,a four-layer non-homogeneous thickening model and a four-layer non-homogeneous core well network model are developed based on the physical parameters of a class of reservoirs in Daqing oilfield.The stability of the adaptive system was evaluated by indoor static experiments;the transport pattern of the adaptive system in the core was studied by a porous percolation long core model,and the microscopic oil repelling mechanism of the adaptive system was studied by combining the microscopic photolithography glass visualization model oil repelling experiment.The optimal concentration of PPG and polymer and the optimal injection volume of the system were selected by the four-layer non-homogeneous thickening model oil repelling experiment.Finally,based on the selected system formulation and injection quantity,the pressure field analysis and oil saturation monitoring of each layer were carried out before and after the adaptive drive using a four-layer non-homogeneous core well network model in a five-point well network model to further investigate the seepage pattern and oil drive effect of the adaptive system.The results show that the optimum molecular weight of polymer is 25 million,the content of surfactant and alkali is 0.2% and 1.2% respectively;the expansion factor of PPG is 3 and the particle size is 0.15-0.3mm,the recovery improvement value of low permeability layer in the adaptive drive stage is 29.91%;the concentration of PPG and polymer in the adaptive system is 400mg/L and 1200mg/L respectively,and the injection volume of the system is 0.5PV,the recovery improvement value of this stage is 19.0%,the total recovery is 71.4%,the water content reduction is 33.1%.The recovery improvement value at this stage is 19.0%,the total recovery rate is 71.4%,the water content reduction rate is 33.1%,and the final diversion rate is23.88% and 15.89% for the middle and low permeability layers respectively.Adaptive drive stage: the pressure from the injection end to the recovery end showed a decreasing trend,showing a more obvious gradient distribution,and the oil-bearing saturation decrease from the extra-high permeability layer to the low-permeability layer increased one by one,and the recovery increase value after well network encryption was 18.4%,which was 2.1% higher than that of one injection and one recovery.