Foam Application in Fractured Carbonate Reservoirs: A Simulation Study

裂缝性碳酸盐岩油藏约占全球石油资源的25%，伊朗石油储量的90%。由于碳酸盐岩的油润湿特性，气体重力排油（GOGD）是主要的生产机制。气体注入裂缝性介质时，主要问题是流体倾向于通过裂缝网络而非基质单元，导致大部分原始油（OOIP）未被扫及。为解决这一问题，泡沫被注入以降低驱替相的流动性，提高注入效率。本文通过CMG STARS 2015软件模拟了泡沫注入过程，研究了影响基质单元中石油提取的三个主要机制：泡沫/油重力排油、裂缝中泡沫流动引起的粘性压力降以及表面活性剂从裂缝向基质的扩散。通过敏感性分析，探讨了泡沫强度、注入速率、裂缝和基质特性、基质高度以及基质中初始油饱和度对石油提取的影响。结果表明，表面活性剂的质量传递和粘性压力降的作用显著，尤其是在基质平均高度较小时。此外，粘性压力降机制在整个过程中保持不变，持续助力石油从基质中提取，而其他两个机制随时间减弱。

CMG软件的应用情况

在本研究中，CMG软件（Computer Modelling Group）被广泛应用于模拟泡沫注入过程，具体应用包括：
  1. 流体模型构建：使用CMG WinPropTM软件创建CO2-油和CO2-盐水混合物的组成和性质。
  2. 模拟实验设计：将流体模型整合到CMG-GEMTM组成的和非传统储层模拟器中，以重现本研究中进行的泡沫注入和CO2-WAG驱替测试。
  3. 结果预测与分析：通过模拟实验结果，预测泡沫注入在高压和高温条件下的表现，并与实验结果进行对比分析，验证模型的准确性。

作者单位

  • Ahmed Zoeir, Mohammad Chahardowli, Mohammad Simjoo  伊朗大不里士沙罕理工大学石油与天然气工程学院

Abstract
Fractured carbonate reservoirs account for 25% of world’s total oil resources and for 90% of Iranian oil reserves. Since calcite and dolomite minerals are oil wet, gas oil gravity drainage (GOGD) is known as the most influencing production mechanism. The most important issue within gas injection into fractured media is the channeling problem which makes the efficiency of gas injection process extremely low. As a solution, foam is used to change the mobility ratio, to increase volumetric sweep efficiency, and to overcome the fingering problem. In this work, we inspected three main influencing mechanisms that affect oil extraction from matrix, namely foam/oil gravity drainage, viscous pressure drop due to foam flow in fractures, and foaming agent diffusion from fractures into the matrixes. Foam injection simulations were performed using CMG STARS 2015, on a single matrix unit model and on some vertical cross section models. A number of sensitivity analyses were performed on foam strength, injection rate, fracture and matrix properties, matrix heights, and the initial oil saturation within matrixes. The results show that the roles of the mass transfer of the foaming agent and viscous pressure drop are significant, especially when matrix average heights are small. Moreover, the mechanism for viscous pressure drop remains unchanged, which continues to aid oil extraction from matrixes while the other two mechanisms weaken with time.

Keywords: Foam, Fractured Reservoir, Gravity Drainage, Gas Invaded Zone, CMG STARS

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