不同边界条件下的渗吸驱动因素

Driving Force for Spontaneous Imbibition Under Different Boundary Conditions

建立不同边界条件下的渗吸数学模型,分别研究在单一边界(OEO边界条件)和混合边界条件(TEO-OW边界条件)下重力和毛管压力对渗吸作用的驱动。结果表明:OEO边界条件下,只存在逆向渗吸,并且当开启端面在下端时,重力抑制渗吸进行;当开启端面在上端时,重力促进渗吸进行;TEO-OW边界条件下,同时存在逆向渗吸和同向渗吸,对于逆向渗吸,重力是阻力,对于同向渗吸,重力是动力,当Bond数倒数较小时,重力在渗吸作用中占主导地位,当Bond数倒数较大时,毛管力占主导地位。对比OEO开启端面在上端时和TEO-OW边界条件下重力和毛管力对渗吸作用的大小。结果显示,在相同Bond数倒数下,OEO边界条件下重力作用的渗吸排油比例要高于TEO-OW边界条件下重力作用的渗吸排油比例。对比不同Bond数倒数下OEO和TEO-OW渗吸速度发现,当Bond数倒数较小时,重力起主导作用,OEO边界渗吸速度更快;当Bond数倒数较大时,毛管力起主导作用,TEO-OW边界条件渗吸速度更快。

Mathematical models of imbibition under different boundary conditions were built with piston-like displacement assumption.Effect of gravity and capillary pressure on imbibition under OEO(single boundary)and TEO-OW(mixed boundary)boundary conditions are studied.It shows that oil is produced only by counter-current imbibition under OEO boundary conditions.Gravity inhibits imbibition as the open face is at the lower end face of core and gravity promotes imbibition as the open face is at the upper end face of core.Oil is produced by combination of co-and counter-current imbibition under TEO-OW boundary condition.Gravity inhibits counter-current imbibition and promotes co-current imbibition under TEO-OW boundary condition.Gravity is dominant driving force as the inverse Bond number is smaller and capillary pressure is dominant driving force as inverse Bond number is greater.In addition,effect of gravity and capillary pressure on imbibition under OEO and TEO-OW boundary conditions are studied.It shows that oil production by gravity under OEO boundary condition is greater than that under TEO-OW boundary condition with same inverse Bond number.The rate of oil production under OEO boundary condition is faster than that under TEO-OW boundary condition as inverse Bond number is smaller and opposite phenomena is observed as inverse Bond number is greater.