基于全直径CT扫描的准噶尔盆地煤层气储层矿物表征及含气量预测

Mineral Characterization and Gas Content Prediction of Coalbed Methane Reservoirs in the Junggar Basin Based on Full-Diameter CT Scanning

  • 摘要: 准噶尔盆地煤层气储层矿物分布特征复杂,尤其是黏土矿物对储层敏感性影响显著,精准识别与评价矿物是优化开发方案、防止储层损害的关键技术难点。为攻克此难点,本文在准噶尔盆地南缘选取四口典型井煤岩样品,采用全直径CT扫描与场发射扫描电镜分析,引入形状因子和灰度值作为核心评价参数,建立了区分煤岩基质、黏土矿物、黄铁矿和方解石的方法,并应用于单井矿物建模、含量计算、储层敏感性评价及含气量预测研究。结果表明:①结合CT灰度值与形态特征(形状因子)综合分析,可有效区分煤岩中煤岩基质、黏土矿物、黄铁矿及方解石。其中方解石的高形状因子(10~50)是其区别于其他矿物(形状因子1~5)的关键识别标志,为基于CT图像的煤岩矿物精准识别与定量分析提供了重要依据;②基于黏土矿物含量建立了储层敏感性分类方法:弱水敏储层(黏土矿物含量<40%)、中等水敏储层(黏土矿物含量40%~70%)、强水敏储层(黏土矿物含量>70%);③构建了黏土矿物含量与实测含气量的显著负相关回归模型(相关系数>0.7),预测含气量平均误差小于10%。④建议在排采过程中,需重点控制中等水敏和强水敏储层的降压速率,以减轻储层损害。本方法基于全井段矿物连续量化模型,揭示了储层垂向非均质性特征及黏土矿物垂向富集带的分布规律;基于黏土矿物空间分布与敏感性分级的耦合关系,中-强水敏区富集带为排采降压控制提供了直接依据;基于黏土矿物含量建立的含气量预测模型,有效支撑地质甜点定位。

     

    Abstract: The complex mineral distribution, particularly clay minerals impacting reservoir sensitivity, poses a key challenge for optimizing development and preventing damage in the Junggar Basin's coalbed methane reservoirs. To address this, coal samples from four wells were analyzed using full-diameter CT scanning and field emission SEM. Shape factor and CT grayscale value were introduced as key parameters, establishing a method to distinguish coal matrix, clay minerals, pyrite, and calcite. This method was applied for mineral modeling, content calculation, sensitivity evaluation, and gas content prediction. Results show: (1) Combined CT grayscale value and shape factor analysis effectively distinguishes minerals; calcite’s high shape factor (10-50) is a key identifier. (2) A reservoir sensitivity classification based on clay content was developed: weak (<40%), medium (40%-70%), and strong (>70%) water sensitivity. (3) A significant negative correlation model (R>0.7) between clay content and measured gas content was built, with prediction errors <10%. (4) Controlled depressurization rates are recommended for medium-strong sensitivity zones during drainage. Key breakthroughs include revealing vertical heterogeneity and clay enrichment via continuous quantification, coupling spatial clay distribution with sensitivity for drainage control guidance, and supporting “sweet spot” identification via the gas content prediction model.

     

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