变质岩裂缝扩展特征及矿物组成对裂缝扩展的影响以渤海湾盆地锦州25-1南油田太古宇潜山油藏为例

    Fracture propagation characteristics of metamorphic rocks and the influence of mineral composition: a case study of buried hill reservoir of Taipaleoyu in Jinzhou 25-1 South Oilfield, Bohai Bay Basin

    • 摘要: 潜山具有巨大的勘探价值,近年来成为了渤海湾海域的勘探热点。为了研究渤海湾潜山变质岩在应力作用下的裂缝扩展特征,本文以渤海湾盆地锦州25-1南油田太古宇潜山变质岩为研究对象,采用实时X-射线CT扫描单轴压缩试验分析不同岩性裂缝扩展特征,并且对破坏后的试样进行矿物定量分析,研究矿物组成对裂缝扩展的影响。研究表明,在单轴压缩条件下,与应力方向夹角较小的垂向高角度初始裂纹比水平初始裂纹更容易发生扩展;峰值强度前的屈服变形阶段是试样加载过程中裂缝扩展最主要的阶段;在相同的应变条件下,二长片麻岩裂缝最发育,其次是斜长片麻岩和混合片麻岩;主裂缝多沿着断裂韧性小的矿物和矿物界面发生扩展,二长片麻岩中通过形成更多的弱矿物界面(如:钾长石-斜长石界面、钾长石-黑云母界面)促进裂缝的发育,且多种含量相近的矿物混合分布对裂缝扩展有积极影响。微裂缝扩展后可作为优质储集空间和渗流通道,以上研究成果对预测岩性控制下潜山构造裂缝发育程度具有指导意义,对锦州25-1南油田开发方案的制定有一定参考价值。

       

      Abstract: The buried hill has great exploration value and has become a hot spot of exploration in Bohai Bay in recent years. In order to study the fracture propagation characteristics of metamorphic rocks in Bohai Bay buried hill under stress, this study focuses on the Archean metamorphic rocks from the buried hills in the Jinzhou 25-1 South Oilfield, located in the Bohai Bay Basin. Real-time X-ray CT scanning uniaxial compression tests were employed to analyze the fracture propagation characteristics of different lithologies, and quantitative mineral analyses were conducted on the damaged samples to study the influence of mineral composition on fracture propagation. Results indicate that, under uniaxial compression, vertical high-angle initial cracks oriented at smaller angles relative to the stress direction are more prone to propagation than horizontal initial cracks. The yield deformation stage preceding peak strength emerges as a crucial phase for fracture propagation during specimen loading. Under identical strain conditions, monzogneiss exhibits the most developed fractures, followed by plagiogneiss and migmatite gneiss. The major fractures mostly propagate along minerals and mineral interfaces with low fracture toughness. Additionally, the formation of more weak mineral interfaces (such as those between potassium feldspar-plagioclase and potassium feldspar-biotite) within monzogneiss facilitates fracture development, and the mixed distribution of various minerals with similar contents has a positive impact on fracture propagation. Microfractures can be used as high-quality reservoir space and seepage channel after expansion. The above research results have guiding significance for predicting the development degree of structural fractures in buried hills under lithology control, and have certain reference value for formulating development plan of Jinzhou 25-1 South oilfield.

       

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