一种计算水驱油藏高含水期驱油效率的新方法

A New Method for Calculating Oil Displacement Efficiency of Water Drive Reservoirs at High Water Cut Stage

常规驱油效率一般通过非稳态相渗的办法计算,但行业标准中的相渗实验条件并不适合特高含水期条件下,多倍水驱后特高含水期的驱油效率难以确定。基于张型广适水驱特征曲线计算推导油田动态数据与驱油效率间的内在联系,从文献已推出的含水率与采出程度关系出发,利用Welge方程中油水两相区间平均含水饱和度与出口端含水饱和度的理论关系,推导出一种计算水驱油藏高含水期驱油效率的新方法。基于张型广适水驱特征曲线推导出油田驱油效率,可以计算含水率为99.9%~99.999%下的极限驱油效率。该方法 推导出的极限驱油效率可以在一定程度上反映高驱替倍数水驱条件下特高含水期驱油效率的定量表征问题,拓展了张型广适水驱特征曲线的应用,解决了疏松砂岩油藏取心困难以及多倍水驱后不同阶段驱油效率确定的难题。

The oil displacement efficiency generally calculated by unsteady relative permeability is hard to be determined at ultra-high water cut stage after multiple pore volumes of water flooding for the experiment conditions of relative permeability in the industry standard are not suitable for that at ultra-high water cut stage.Based on the internal relationship between oilfield dynamic data and oil displacement efficiency calculat-ed and derived by Zhang′ s type water drive characteristic curve,starting from the relationship between water cut and recovery degree introduced in the literature,a new method for calculating oil displacement efficiency of water drive reservoirs at high water cut stage is proposed using the theoretical relationship between aver-age water saturation in oil-water two-phase interval and water saturation at outlet in the Welge equation.Based on the oil displacement efficiency of the oilfield derived by Zhang ′ s type water drive characteristic curve,ultimate oil displacement efficiency at water cut of 99.9%-99.999% can be calculated.The ultimate oil displacement efficiency deduced by the new method can reflect the quantitative characterization of oil dis-placement efficiency at ultra-high water cut stage under the condition of high pore volume of water drive to a certain extent,which expands the application of Zhang′ s type water drive characteristic curve and solves the difficulty of coring in loose sandstone reservoirs and determining oil displacement efficiency at different stages after multiple pore volume of water flooding.