改进的混合单元格法预测最小混相压力

An effective way to forecast minimum miscibility pressure based on improved multiple-mixing-cell approach

 张晨朔 范子菲 许安著 赵伦

 （中国石油勘探开发研究院，北京 100083）

 (Research Institute of Petroleum Exploration & Development, PetroChina, Beijng 100083, China)

 最小混相压力（MMP）是确定油藏能否达到混相驱的关键参数。混合单元格法作为一种计算MMP的方法具有快速、方便的优点，但在实际应用中常常难以找到斜率为0的关键系线，并且需要在临近MMP时作指数式拟合外推，从而导致预测结果存在较大的不确定性。为此，文中提出一种基于系线长度最小值变化规律的改进混合单元格方法。首先利用混合单元格法的气液混合过程计算得到系线长度曲线，研究系线长度曲线和临界点随压力的变化规律，提出了改进混合单元格方法的计算步骤，最后通过实例进行对比验证。研究表明，改进的混合单元格法克服了原方法搜索关键系线的不稳定性和参数拟合的不确定性。通过与4组已发表的算例对比，该方法与混合单元格法、系线解析法和细管实验法具有相近的计算结果，平均相差分别为1.07%，5.15%和4.20%，具有较好的稳定性和较高的预测精度。

 The minimum miscibility pressure(MMP) is the key parameter to evaluate the miscibility during displacement under a given reservoir pressure. Multiple-mixing-cell approach is fast and convenient, however, it relies on finding the unique key tie line with 0 value, which can be difficult and the multiple-parameter regression used for extrapolation usually leads to inaccurate results. Therefore, an effective way was developed to forecast MMP: the improved multiple-mixing-cell approach relying on the transition of tie line in pressures. In this paper, the tie line length is calculated using the mixing contacts from multiple-mixing-cell approach, and the influence patterns of pressure on tie line and critical point are researched. After that, a novel procedure in detail is introduced to improve the multiple-mixing-cell approach. Finally, this approach is verified by contrast calculation using multiple-mixing-cell approach, analytical method of characteristics, and slim tube experiment in 4 cases. The study indicates that this new method can fix the uncertainty and inaccuracy of key tie lines searching and regression. The MMP results calculated from improved multiple mixing cell approach differ by 1.07%, 5.15% and 4.20% respectively from other methods, which shows that this method is accurate and robust.

10.6056/dkyqt201605014