深层低渗致密气藏甜点预测与分类评价方法——以东海盆地西湖凹陷中央背斜带南部X气田平湖组为例

An evaluation method for sweet spot prediction and classification in deep low-permeability tight gas reservoirs: a case study of Pinghu Formation in gasfield X of southern central anticline belt, Xihu Sag, East China Sea Basin

  • 摘要: 针对东海西湖凹陷中央背斜带南部始新统平湖组储层埋藏深(>3 900 m)、非均质性强、低渗致密制约气藏效益开发的难题,提出一套融合岩性、物性与含气性特征的深层低渗致密气藏甜点综合识别与分类评价方法。通过开展储层分类建模与流体替换AVO分析,明确了速度比与泊松阻抗对岩性敏感,泊松阻尼因子对物性敏感,流体因子与体积模量对含气性敏感。基于AVO响应特征,建立了四级甜点的地球物理响应模式。依托相控叠前弹性反演,计算速度比、泊松阻抗、泊松阻尼因子、流体因子及体积模量等关键参数,实现了储层岩性、物性及含气性等综合预测。进一步提出基于稀疏主成分分析(Sparse PCA)与自适应权重(Adaptive Weighting)的多属性甜点评价框架(SPCA-AW),通过L1正则化实现属性载荷稀疏化来自动筛选主要地震属性,并依据稀疏度与载荷强度构建自适应权重以提升属性融合效果,最终优选出物性好、气饱高的优质甜点。该方法在气田目标层位的应用表明,预测结果与测井解释及试气成果的综合匹配率超过80%,有效识别了气藏甜点发育有利区带,为深层低渗致密气藏的滚动评价、井位部署及效益开发提供了可靠依据。

     

    Abstract: The study aims to address the challenges of developing gas reservoirs in the Eocene Pinghu Formation of the southern part of the central anticline belt in the Xihu Sag, East China Sea Basin, which are characterized by deep burial (>3 900 m), strong heterogeneity, and low-permeability tightness limiting gas production. A comprehensive evaluation method for sweet spots identification and classification in deep, low-permeability, tight gas reservoirs, integrating lithology, physical properties, and gas-bearing characteristics, was proposed. By conducting reservoir classification modeling and amplitude variation with offset (AVO) analysis via fluid replacement modeling, it was clarified that the velocity ratio and Poisson impedance were sensitive to lithology, the Poisson damping factor was sensitive to physical properties, and the fluid factor and bulk modulus were sensitive to gas-bearing properties. Based on AVO response characteristics, a geophysical response pattern for four classes of sweet spots was established.Relying on facies-controlled pre-stack elastic inversion, key parameters such as velocity ratio, Poisson impedance, Poisson damping factor, fluid factor, and bulk modulus were estimated to achieve a comprehensive prediction of reservoir lithology, physical properties, and gas-bearing characteristics. A multi-attribute sweet-spot evaluation framework based on sparse principal component analysis (SPCA) and adaptive weighting (AW) was further proposed. The L1-regularization was used to enable sparsity in attribute loadings to automatically screen the main seismic attributes, and adaptive weights were constructed based on sparsity and loading strength to improve attribute fusion, ultimately selecting high-quality sweet spots with good physical properties and high gas saturation. Application of this method to target layers in the gas field showed that the comprehensive matching rate between the prediction results and the well log interpretation and gas testing results exceeded 80%. This approach effectively identified favorable zones for sweet spot development in gas reservoirs, providing a reliable basis for rolling evaluation, well location deployment, and efficient development of deep, low-permeability, tight gas reservoirs.

     

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