变质岩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

    The influence of metamorphic rock mineral composition on fracture propagation: a case study of buried-hill reservoir of Archean 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-斜长石界面和钾长石-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. To study the fracture propagation characteristics of metamorphic rocks in buried hill in the Bohai Bay under stress, the Archean metamorphic rocks from the buried hills in the Jinzhou 25-1 South Oilfield were studied. Real-time X-ray CT scanning uniaxial compression tests on three types of rock specimens, i.e., monzogneiss, plagiogneiss, and migmatitic gneiss were performed to analyze the fracture propagation characteristics. Quantitative mineral analyses were conducted on damaged samples to study the influence of mineral composition on fracture propagation. Results indicate that, under the uniaxial compression, vertical high-angle initial cracks at smaller angles relative to the stress direction are more prone to propagation than horizontal ones. The yield deformation stage before peak strength is the crucial phase for fracture propagation during specimen loading. Under the same strain conditions, monzogneiss specimen showed the most developed fractures, followed by plagiogneiss and migmatitic gneiss specimens. The major fractures propagated mostly along minerals and mineral interfaces with low fracture toughness. Additionally, the formation of more weak interfaces of mineral (such as those between potassium feldspar-plagioclase and potassium feldspar-biotite) in monzogneiss favored the fracturing, and the distribution of various minerals with similar contents had a positive impact on fracture propagation. After expansion of microfractures, they can be used as high-quality reservoir space and seepage channel. This study provided a guidance for predicting the degree of fracture development in buried hill structures under lithological control, and a certain reference value for formulating development plan of Jinzhou 25-1 South Oilfield.

       

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