36 / 2025-11-19 10:58:01

超临界CO2等流体对页岩力学特性及可压裂性的影响研究 Effects of Supercritical CO₂ and Other Fluids on the Mechanical Properties and Fractability of Shale

作为破解能源供需困局、维护国家能源安全的关键战略路径，页岩气高效开发已成为我国能源战略的重大需求。然而国内页岩气储层普遍埋藏较深，因此开展高温高压条件下超临界CO₂作用对页岩力学性能以及可压裂性的影响研究对深入了解超临界CO₂强化深部页岩气开采和CO₂地质封存具有重要意义。本研究以牛蹄塘组页岩为研究对象，通过高温（100 ℃）、高压（15 MPa、30 MPa、45 MPa以及60 MPa）条件下不同流体（超临界CO₂、水以及超临界CO₂+水）与页岩的相互作用实验系统研究了流体浸泡对页岩力学性能、矿物组分、微观结构及可压裂性的影响规律。研究结果表明：超临界CO2等流体均会导致页岩的力学特性弱化，其影响程度由大到小依次为超临界CO₂+水、纯水、超临界CO₂。在矿物组分及微观结构方面，超临界CO₂主要促进微孔隙发育，水浸泡引起长石、黄铁矿等矿物溶蚀，而超临界CO₂+水复合作用进一步加剧矿物溶蚀与元素释放，并形成复杂裂缝网络。声发射监测显示，超临界CO₂及其复合体系促进裂纹扩展，事件多集中于不稳定裂纹阶段，且分形维数分析揭示其破坏模式存在显著差异。在工程指标方面，随浸泡压力升高，超临界CO₂单独作用可提升页岩脆性指数，而水与复合流体因水化软化作用使脆性普遍降低。三种流体作用均使页岩可压裂性指数随压力上升而提高，尤以超临界CO₂+水作用条件提升最为显著。本研究揭示了超临界CO₂与地层水协同作用对深部页岩力学行为与压裂潜能的强化机制，为深部页岩气绿色高效开发及CO₂封存一体化技术提供了理论依据。

As a crucial strategic approach to addressing energy supply-demand challenges and safeguarding national energy security, the efficient development of shale gas has become a significant requirement within China's energy strategy. However, given that shale gas reservoirs in China are generally deeply buried, investigating the effects of supercritical CO₂ under high-temperature and high-pressure conditions on the mechanical properties and fractability of shale is of great importance for understanding enhanced deep shale gas extraction and CO₂ geological sequestration. This study focuses on the shale from the Niutitang Formation, systematically investigating the effects of fluid immersion—using supercritical CO₂, water, and a supercritical CO₂-water mixture under high temperature (100°C) and high-pressure conditions (15 MPa, 30 MPa, 45 MPa, and 60 MPa)—on the mechanical properties, mineral composition, microstructure, and fractability of shale. The results indicate that all fluids lead to the weakening of the mechanical properties of shale, with the degree of impact in descending order as follows: supercritical CO₂ + water, pure water, and supercritical CO₂. In terms of mineral composition and microstructure, supercritical CO₂ primarily promotes the development of micropores, water immersion leads to the dissolution of minerals such as feldspar and pyrite, while the combined action of supercritical CO₂ and water further exacerbates mineral dissolution and element release, forming a complex fracture network. Acoustic emission monitoring reveals that supercritical CO₂ and its combination with water promote crack propagation, with events predominantly concentrated in the unstable crack growth stage. Fractal dimension analysis further indicates significant differences in the failure modes induced by different fluids. Regarding engineering indicators, as the immersion pressure increases, supercritical CO₂ enhances the brittleness index of shale, whereas water and the supercritical CO₂-water mixture reduce brittleness due to hydration softening effects. All three fluid treatments result in an increase in the fractability index of shale with rising pressure, with the most significant enhancement observed under the supercritical CO₂-water condition. This study reveals the synergistic mechanism of supercritical CO₂ and formation water in enhancing the mechanical behavior and fracturing potential of deep shale, providing a theoretical basis for the integrated technology of green and efficient deep shale gas development and CO₂ sequestration.