Abstract: The self-sealing capacity of shale is a critical factor for the enrichment and accumulation of shale oil and gas. However, the current understanding of the self-sealing mechanism of shale oil and gas reservoirs remains insufficient, which severely restricts the development of unconventional oil and gas geology theories and the advancement of hydrocarbon exploration in China. An in-depth research on the self-sealing mechanisms and differences regarding typical marine shale gas will contribute to improving the unconventional hydrocarbon accumulation theories and guiding the exploration and development practice. This study focuses on the Longmaxi Formation shale in Sichuan Basin, and comprehensively using petroleum geology theory, nanoscale water film theory, and adsorption thermodynamics theory, as well as gas reservoir analysis, fine-scale reservoir characterization and theoretical calculations, the following three research achievements have been obtained. (1)This study clarifies the geological characteristics of the self-sealing system of Longmaxi Formation shale gas in Sichuan Basin, discovers the vertical variation patterns and differences in the total organic carbon (TOC)content, pore structure, and fluid characteristics of the shale. These factors serve as important geological foundations for the formation of the shale gas self-sealing system. (2)The study reveals the microscopic self-sealing mechanism in shale gas reservoirs. The tight shale reservoirs with poor pore connectivity facilitate physical self-sealing. The complex organic-inorganic pore system of shale, along with its gas-water distribution patterns, jointly contribute to the capillary force-driven self-sealing effect. This effect is dually controlled by pore structure and water saturation. Moreover, the adsorption capacity of shale can result in self-sealing capacity, which is primarily related to the specific surface area and TOC content of the shale, and is particularly remarkable in organic-rich shale. (3)An analysis has been performed on the vertical differences in self-sealing effects. The upper gas reservoir is dominated by capillary force-driven self-sealing, followed by physical self-sealing. In contrast, the lower gas reservoir exhibits a composite mechanism involving physical self-sealing, capillary force-driven self-sealing, and adsorption force-driven self-sealing. The research results are expected to provide valuable insights for improving the theoretical system of unconventional oil and gas accumulation, and guiding exploration and development practices.

Key words: self-sealing mechanism, difference analysis, shale gas, Longmaxi Formation, Sichuan Basin

摘要： 页岩的自封闭性是页岩油气富集成藏的关键因素,然而目前对页岩油气自封闭成藏机制的认识仍不够深入,这严重制约了中国非常规油气地质理论的发展和勘探工作的推进。深入研究典型海相页岩气的自封闭机理及差异,有助于完善非常规油气成藏理论,指导非常规油气勘探开发。以四川盆地龙马溪组页岩为研究对象,综合运用石油地质理论、纳米水膜理论和吸附热力学理论,通过气藏解剖、储层精细表征和理论计算等方法,取得了3方面的研究成果:①明确了四川盆地龙马溪组页岩气自封闭体系的地质特征,揭示了页岩纵向总有机碳(TOC)含量、孔隙结构和流体特征的变化规律及其差异性。这些因素是形成页岩气自封闭体系的重要地质基础。②揭示了页岩气自封闭的微观机理。页岩储层具有致密性和孔隙连通性差的特征,这有利于形成物性自封闭作用。页岩复杂的有机-无机孔隙系统及其气-水分布特征共同构成了毛细管力自封闭作用,该作用受孔隙结构和含水饱和度双重控制。同时,页岩本身具有一定的吸附能力,可形成吸附力自封闭作用,该作用主要与页岩的比表面积和TOC含量相关,在富有机质页岩中表现得尤为显著。③分析了页岩气自封闭作用在纵向上的差异性。上部气藏以毛细管力自封闭作用为主导,物性自封闭作用次之;而下部气藏则呈现出物性自封闭作用、毛细管力自封闭作用和吸附力自封闭作用三者并存的复合特征。研究成果以期为完善非常规油气成藏理论体系和指导勘探开发实践提供借鉴。

关键词: 自封闭机理, 差异分析, 页岩气, 龙马溪组, 四川盆地