页岩储层粘土矿物对裂缝导流能力伤害的影响

摘 要 页岩气的有效开发依赖于人工裂缝的产生，而要持续高效的进行页岩气开发，需要采用支撑剂保持人工裂缝的导流效果。目前，对于页岩储层支撑裂缝导流能力伤害的微观机理尚不清楚。本文以中国南方海相页岩为研究对象，开展岩板导流能力伤害实验，并与致密砂岩和常规砂岩进行对比，分析压裂液注入过程中导流能力变化规律。结果显示随着压裂液的持续注入，大量的支撑剂逐渐嵌入裂缝内，引起导流能力下降。初期导流能力下降较快，后期降速逐渐减缓。海相页岩支撑裂缝的导流能力伤害程度大幅度高于常规储层。常规储层支撑裂缝导流能力伤害率约为18%，而海相页岩的支撑裂缝导流能力伤害率约为47%~85%。导流能力伤害率与粘土矿物含量和类型关系密切。随着粘土矿物含量的提高，导流能力伤害率迅速升高，尤其是伊利石和伊蒙混层存在可以明显提高导流能力伤害率。粘土矿物具有极强的吸水膨胀能力，易引起支撑裂缝表面硬度软化、蠕变强化，导致支撑剂嵌入和导流能力下降。本文通过页岩导流能力实验，分析了压裂液注入过程中导流能力变化规律及粘土矿物含量对导流能力伤害率的影响，为优化压裂液配方、改进页岩气井排采制度和提高页岩气的产出具有重要意义。

Effect of clay minerals in shale reservoirs on fracture conductivity

The effective development of shale gas depends on the generation of artificial cracks, and the continuous and efficient development of shale gas requires proppant to maintain the effect of artificial cracks. At the same time, to ensure the efficient development of shale gas, the conductivity of artificial fracture network must be maintained. At present, the microscopic mechanism of damage to the fracture conductivity of shale reservoirs is still unclear. In this paper, the marine shale in southern China is taken as the research object, and the experiment of rock plate diversion ability damage is carried out, and compared with tight sandstone and conventional sandstone, the variation law of the conductivity of fracturing fluid during the injection process is analyzed. The results show that with the continuous injection of the fracturing fluid, a large amount of proppant is gradually embedded in the crack, causing the conductivity to decrease. The initial diversion capacity decreased rapidly, and the subsequent deceleration gradually slowed down. The degree of damage of the conductivity of the marine shale support crack is much higher than that of the conventional reservoir. The damage rate of conventional reservoir support fracture conductivity is about 18%, while the damage rate of support fracture conductivity of marine shale is about 47%~85%. The rate of damage to the conductivity is closely related to the content and type of clay minerals. With the increase of clay mineral content, the damage rate of the conductivity is rapidly increased, especially the presence of illite and Yimeng can significantly improve the damage rate of the conductivity. Clay minerals have a strong ability to absorb water and swell, which tends to cause softening and creep strengthening of the surface of the supporting cracks, resulting in a decrease in proppant embedding and conductivity. In this paper, the shale conductivity experiment is used to analyze the variation of the conductivity of the fracturing fluid and the influence of the clay mineral content on the damage rate of the conductivity. In order to optimize the fracturing fluid formulation, improve the shale gas well drainage system and It is important to increase the output of shale gas.