Reservoir heterogeneity and its role in long-term CO₂ storage performance: A case study of Air Benakat formation

为支持印尼2050年实现碳中和目标，本研究以南苏门答腊盆地的Air Benakat组为研究对象，评估其在不同储层非均质性条件下的CO₂地质封存效果。通过构建均质与不同非均质性（Lorenz系数 Lk = 0.0、0.2、0.4、0.6）条件下的储层模型，模拟了CO₂注入30年及后续1000年的运移与封存过程。

本研究强调了在CCS项目中考虑储层非均质性的必要性，以提高封存量评估的准确性和长期安全性。

CMG软件应用情况

  • 软件平台：CMG-GEM（Compositional Simulator）
  • 模拟方法：
    • 使用WINPROP进行流体PVT性质建模，构建Peng-Robinson状态方程；
    • 构建三维组分模型（100×100×60网格，共60万个网格块）；
    • 模拟CO₂注入30年及后续1000年的运移、封存机制（自由相、残余相、溶解相）；
    • 应用Lorenz系数（Lk）量化储层渗透率非均质性，比较不同Lk值下的CO₂封存行为；
    • 未考虑地球化学反应（如矿物封存）和地质力学耦合。

主要结论

  1. 注入期压力控制：储层非均质性越强，注入期峰值压力越低（Lk=0.6时比均质模型降低63 psi，降幅3.69%）。
  2. 封存机制转化：随着非均质性增强，CO₂由自由相和残余相向溶解相转化更为显著，Lk=0.6时溶解封存比例达72%，比均质模型高29.4%。
  3. 羽状流迁移特征：非均质性增强导致CO₂羽状流横向更不对称、分散，垂向分布更复杂，最大横向扩展面积增加23.4%。
  4. CCS选址与风险评估建议：应基于非均质模型进行封存容量评估、注入压力设计及监测井布设，避免高估封存能力。

作者单位

印尼廖内伊斯兰大学石油生产研究中心（PSP3MB）/ 美国德克萨斯大学奥斯汀分校地球与行星科学系

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Abstract

Indonesia’s strategy for attaining net-zero emissions by 2050 is contingent upon carbon capture and storage (CCS). The long-term CO₂ storage performance of Air Benakat formation in the South Sumatra Basin was assessed in this study, with a particular emphasis on the influence of reservoir heterogeneity. We compared the behavior of CO₂ (trapping mechanisms and migration) under homogeneous and heterogeneous conditions by utilizing reservoir modeling. Sequential Gaussian simulation (SGS) was implemented to represent spatial variability in porosity and permeability. Increased degrees of heterogeneity are quantified by Lorenz coefficients of permeability (Lk) of 0.0, 0.2, 0.4, and 0.6. The simulation results over a 1000-year period indicate that pressure accumulation during the 30-year injection phase is reduced, and pressure dissipation is enhanced post-injection as a consequence of increased heterogeneity. The distribution of permeability substantially impacts the trapping mechanisms for CO₂, including free-phase (supercritical), residual (trapped), and dissolved. Heterogeneous models exhibit greater long-term dissolution as a result of flow redistribution, whereas homogeneous models retain a larger amount of free-phase and trapped CO₂. Moreover, the consequences of heterogeneity are further illustrated by plume migration patterns. With the increase in Lk values, lateral migration becomes more asymmetric and fragmented, and the plume area expands by up to 23.4 % in comparison to the homogeneous case. Heterogeneity redirects CO₂ into additional strata without altering the maximal height, as evidenced by vertical plume analysis, with occupancy differences reaching up to 9.2 %. Overall, results highlight that ignoring heterogeneity leads to overestimations in CO₂ storage efficiency, particularly in trapped CO2 capacity.

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