大庆中低渗油层聚合物驱可行性室内实验研究

A Laboratory Experimental Study of Feasibility of Polymer Flood for Middle-Low Permeability Reservoirs in Daqing

对可用于大庆油田中低渗油藏聚合物驱的聚合物HPAM的适宜分子量进行了研究.取聚合物溶液粘度为12 mPa·s(45℃,7.34 s-1),由粘浓曲线求得分子量为2.4×106、5.0××106、8.0×106及1.0×107的聚合物溶液浓度应分别为1000、800、600、400 mg/L.指出油藏孔隙半径中值大于聚合物分子线团回旋半径的5倍时,聚合物不会堵塞该油藏.在水相渗透率为9.87×10-3～22.0×10-3 μm2的18支储层岩心上,用不同分子量、不同浓度的聚合物溶液测定阻力系数和残余阻力系数,根据注聚合物时和后续注水时注入压差的变化和残余阻力系数值,判断聚合物是否堵塞岩心,确定上述不同分子量聚合物分别适用于水相渗透率为0.01、0.03、0.10、0.20 μm2的油藏.在渗透率为0.130～0.214 μm2的岩心上,用粘度～12 mPa·s的聚合物溶液驱油,注入量～1 PV,分子量1.0×107的聚合物对岩心造成堵塞,其余分子量的聚合物提高采收率的幅度,由分子量2.4×106时的6.5%提高到分子量8.0×106时的7.6%.结合试验区先期注入井的结果,分子量8.0×106的聚合物可用于大庆油田大多数中低渗油藏,分子量超过8.0×106时有一部分油藏会发生堵塞.数值模拟表明,在分子量6.5×106、聚合物用量420 (mg/L)·PV、注入流量0.15 PV/a条件下,聚合物溶液浓度由400 mg/L增至1200 mg/L时,采收率增值仅由6.75%增至7.25%.图1表4参3.

The molar mass (MM) of polymer HPAM suitable for use in polymer flood in middlle-low permeability reservoirs of Daqing is studied.Supposing that the polymer solution viscosity is of 12 mPa.s, the solution concentration for polymers of MM 2.4×106, 5.0×106, 8.0×106, and 1.0×107is ascertained to be of 1000, 800,600, and 400 mg/L, respectively, according to their viscosity (45℃, 7.34 s-1)—concentration curves.It is stated that a given reservoir might not be plugged by a polymer with coil gyration radius smaller than 1/5 of the pore radius median.On 18 reservoir cores of water phase permeability 9.87×10-3—220.2×10-3 μm2, the resistance factor and the residual resistance factor (RRF) are measured for polymers of different MM in solution of different concentration, the changes in injecting pressure of polymer solution and of successive water and theRRFvalue measured indicate whether blockages are creacted in a core or not and the above mentioned polymers with different MM are shown to be suitable to reservoirs of permeability 0.01, 0.03, 0.10, and 0.20μm2, respectively.On reservoir cores of permeability 0.130—0.214μm2 injecting ~1 PV of polymer solution of viscosity ~ 12 mPa.s leads to enhancement in oil recovery (EOR) increased with polymer MM from 6.5% for MM=2.4×106to 7.6% for MM=8.0×106meanwhile polymer of MM=1.0×107creates blockages in cores. Taking into consideration the results of preliminary pilot wells, it is concluded that polymers of MM=8.0×106can be used in most middle-low permeability reservoirs of Daqing and blockage creation will occur in some of such reservoirs with polymers of MM>8.0× 106.A digital simulation investigation shows that by using polymer solutions of concentration increased from 400 to 1200 mg/L under conditions of MM=6.5×106, polymer use level 420 ( mg/L).PV and injecting flow rate 0.15 PV/a, the EOR increases from 6.75% to 7.25% merely.