水相分流量全过程有理式模型的建立及应用

Establishment and application of whole process rational formula model of water fractional flow

水相分流量曲线是研究油藏开发动态的重要基础资料之一,主要获取途径是室内实验测试。受实验周期及实验设备限制,注入量有限,无法直接得到水相分流量曲线端点值。现有的计算模型基本未考虑极限驱替,曲线端点值无法通过拟合计算获得。基于油藏工程理论,明确水相分流量曲线的理论关系、曲线特征和边界条件。通过对比分析多种数学模型,确定采用有理式函数为基础形式建立水相分流量的全过程模型。结果表明,模型计算值与实测值的平均相对误差仅为0.4%,计算精度高,能够实现极限驱替时刻残余油饱和度预测以及相对渗透率比值全过程曲线的计算。研究过程所需参数可从相对渗透率测试报告中获取,数学模型具有较高的普及性和实用性,能够为水驱油藏开发的理论极限、剩余开发潜力及下一步调整方向提供指导和帮助。

The curve of water fractional flow is of vital importance to the research on reservoir development,which can be achieved by laboratory test.The endpoint value(water saturation)of this curve cannot be obtained directly owing to insuffi⁃cient injection volume limited by experimental period and instruments.Also,the endpoint value cannot be calculated by fit⁃ting because current calculation models neglect limit displacement.Based on the reservoir engineering theory,the theoreti⁃cal relationship,characteristics,and boundary condition of the curve of water fractional flow were specified.The rational for⁃mula is chosen for building the whole process model of water fractional flow through the comparison of multiple mathemati⁃cal models.The results show that the rational formula model has high accuracy as the average relative error between calcu⁃lation value and test value is 0.4%,for which it can be used for forecasting the residual oil saturation data at the point of limit displacement and calculating the whole process curve of relative permeability ratio.This rational formula model has great practicality and can be widely adopted because the parameters in the calculation are accessible in the test report on relative permeability.More importantly,it can provide some guidance for the theoretical limit,surplus potential,and direc⁃tion adjustment of the development of water drive reservoirs.