非常规能源在开发过程中涉及压裂，二氧化碳（CO₂）压裂不仅可以强化页岩气开采效果，还能够就地封存CO₂和实现开采过程的碳中和，是一种具有发展前景的页岩气开采技术。本文通过物理模拟实验、理论分析以及数值模拟实验等方法，明确了CO₂ 压裂破裂压力和裂缝扩展形态的影响因素，分析了裂缝扩展时空演变规律，系统地研究了页岩CO₂ 压裂裂缝扩展规律。本文的研究方法和结论可供后续探究页岩等非常规储层CO₂ 压裂裂缝扩展影响因素以及裂缝扩展机理作为参考。本文主要研究内容与结论如下：

（1）利用氦孔隙仪测量了页岩和砂岩的孔隙度；采用非稳态渗透率测定中的脉冲衰减方法，结合渗透率测量仪获得了页岩和砂岩的渗透率；利用压力试验机通过单轴抗压实验以及巴西劈裂实验，获得了页岩和砂岩的弹性模量、泊松比、抗压强度和抗拉强度。结果表明：相比于砂岩，页岩孔隙度和渗透率更低，抗拉强度更大，非均质性更强。

（2）基于CO₂ 压裂物理模拟实验系统，开展了不同注入速率、不同围压以及不同岩石性质下的CO₂ 压裂实验，分析了页岩CO₂ 压裂过程，研究了页岩CO₂ 压裂破裂压力规律。结果表明：当注入速率超过注入速率阈值后，随着注入速率的升高，页岩破裂压力、凝结相时间和达到破裂压力的时间降低；围压和岩石抗拉强度越大，破裂压力越高。基于实验结果，验证了两个经典的破裂压力公式H-W公式和H-F公式在预测CO₂ 压裂破裂压力中的适用性。

（3）对于页岩CO₂ 压裂裂缝扩展过程的数值模拟，引入了全局嵌入0厚度cohesive单元的有限元模拟方法，减少了压裂裂缝起裂和扩展数值模拟过程人为因素干扰。建立了页岩CO₂ 压裂裂缝扩展模型，研究了注入速率、射孔角度和天然裂缝对CO₂ 压裂裂缝扩展形态的影响规律。结果表明：随着CO₂注入速率升高，裂缝网络趋于复杂；射孔角度和天然裂缝显著影响裂缝走向。

（4）基于压裂实验中声发射信息，还原了CO₂ 压裂裂缝发育过程，结合声学、地震学以及信息论的相关理论，研究了压裂各阶段声发射事件率、b值、RA-AF值和时空熵值等参数的演变趋势，揭示了页岩CO₂ 压裂裂缝扩展规律。结果表明：CO₂ 压裂裂缝扩展过程主要分为三个阶段：阶段1：CO₂ 压缩冷凝阶段；阶段2：裂缝成核成团阶段；阶段3：裂缝的不稳定发展阶段。压裂过程中产生的主导裂缝类型变化为：张拉裂缝-混合裂缝-剪切裂缝，并且整体上剪切裂缝多于张拉裂缝。声发射空间和时间熵值在页岩达到断裂失稳前都会急剧下降。

Fracturing is involved in the exploitation of unconventional energy sources, and carbon dioxide (CO₂) fracturing can not only strengthen the effect of shale gas extraction, but also sequester CO₂ in situ and achieve carbon neutrality in the recovery process, which is a promising shale gas recovery technology. In this paper, through physical simulation experiments, theoretical analysis and numerical simulation experiments, the influence factors of CO₂ fracturing fracture pressure and fracture expansion pattern are clarified, and the spatial and temporal evolution of fracture expansion is analysed, so as to systematically study the fracture expansion pattern of CO₂ fracturing in shale rock. The research methods and conclusions of this paper can be used as a reference for the subsequent investigation of the influencing factors of CO₂ fracturing fracture extension and the fracture extension mechanism in unconventional reservoirs such as shale. The main research contents and conclusions of this paper are as follows:

(1) The porosity of shale and sandstone was measured using a helium porosimeter; the permeability of shale and sandstone was obtained by using the pulse attenuation method in the determination of non-stationary permeability in combination with a permeability meter; and the modulus of elasticity, Poisson's ratio, compressive strength, and tensile strength of shale and sandstone were obtained by uniaxial compression test as well as Brazilian cleavage test using a pressure tester. The results show that shale has lower porosity and permeability, greater tensile strength and greater non-homogeneity than sandstone.

(2) Based on the physical simulation system of CO₂ fracturing, CO₂ fracturing experiments were carried out under different injection rates, different peripheral pressures and different rock properties to analyse the process of CO₂ fracturing in shale, and to study the fracture pressure law of CO₂ fracturing in shale. The results show that when the injection rate exceeds the threshold of the injection rate, the fracture pressure, the condensed phase time and the time to reach the fracture pressure decrease with the increase of the injection rate, and the higher the peripheral pressure and the tensile strength of the rock, the higher the fracture pressure. Based on the experimental results, the applicability of the two classical fracture pressure formulas, H-W formula and H-F formula, in predicting the fracture pressure of CO₂ fracturing is verified.

(3) For the numerical simulation of CO₂ fracturing in shale rock, a finite element simulation method with a globally embedded 0-thickness cohesive unit is introduced to reduce the interference of human factors in the numerical simulation of fracture initiation and extension. A shale CO₂ fracturing fracture extension model was established, and the effects of injection rate, injection angle and natural fractures on the fracture extension pattern of CO₂ fracturing were investigated. The results show that the fracture network tends to be more complicated with the increase of CO₂ injection rate, and the injection angle and natural fractures significantly affect the fracture direction.

(4) Based on the acoustic emission information in the fracturing experiments, the fracture development process of CO₂ fracturing is restored, and the evolution trends of parameters such as acoustic emission event rate, b-value, RA-AF value and spatial and temporal entropy value at each stage of fracturing are investigated by combining acoustic, seismic and information theory theories, so as to reveal the fracture expansion pattern of CO₂ fracturing in shale rock. The results show that the fracture expansion process of CO₂ fracturing is mainly divided into three stages: Stage 1: CO₂ compression and condensation stage; Stage 2: fracture nucleation and clustering stage; and Stage 3: unstable development of fracture. The dominant fracture types generated in the fracturing process change to: tension fracture-mixed fracture-shear fracture, and overall there are more shear fractures than tension fractures. Both spatial and temporal entropy values of acoustic emission decrease dramatically before the shale reaches fracture instability.