高含水期油田水驱特征曲线关系式的理论推导

传统水驱特征曲线推导的理论基础是中含水阶段油水相对渗透率比(Kro/Krw)与含水饱和度(Sw)成半对数直线关系,而在高含水阶段Kro/Krw与Sw在半对数坐标中明显偏离直线关系,水驱特征曲线普遍存在上翘现象。为了准确预测油田开发后期开发动态和可采储量,对实际岩心相对渗透率曲线进行平均化处理,并借鉴文献中岩心数据资料,拟合出适合高含水阶段Kro/Krw与Sw关系的新型表达式;应用Buckley-Leverett前沿推进方程和Welge平均含水饱和度方程,推导出适合高含水期油田的新型水驱特征曲线关系式。应用分析表明,新方法预测水驱可采程度与产量递减方法计算结果吻合度较好,对于油田生产后期开发指标预测具有一定的实用性。

Derivation of water flooding characteristic curve for high water-cut oilfields

The linear relationship between relative permeability ratio (Kro/Krw) and water saturation (Sw) on the semi-log coordinate in the stage of middle water-cut is the theoretical basis for the derivation of traditional water flooding characteristic curves. However, the relationship of Kro/Krw versus Sw deviates from the straight line in the high water-cut stage, which results in the upwarping of water flooding characteristic curve. In order to accurately predict the production performance and recoverable reserves in the late development stage, the relative permeability curves of actual cores were averaged. Furthermore, using the core data in the reference, a new expression of Kro/Krw versus Sw was obtained by regression for the high water-cut stage. On the basis of the frontal-drive equation and the average water saturation equation proposed respectively by Buckley-Leverett and Welge, a new water flooding characteristic curve was derived which is more applicable for high water-cut oilfields. The calculation results indicate that the recoverable reserves calculated by the new approach is almost equal to the result of the production decline method, proving it is a practical tool in the prediction of production indexes in the late development stage of oilfields.