特提斯域板块构造约束下上扬子地区二叠系龙潭组页岩气的差异性赋存

全球页岩气勘探开发在海相页岩中取得了巨大成功，在海-陆过渡相和陆相页岩中也进行了积极探索，但尚未形成商业开发局面。在分析华南地区二叠纪板块构造对原型盆地和富有机质页岩形成分布控制的基础上，研究了龙潭组岩相、地化、矿物组合、储层特征，通过与具有相似沉积背景且已进行商业开发的国内外典型页岩层系的对比，明确了龙潭组海-陆过渡相-海相页岩气赋存特征及资源前景。研究认为：①受秦岭洋和金沙江洋俯冲消减的拖拽作用和“峨眉地裂运动”等构造事件的影响，扬子台地内部和边缘分别发育了一系列的裂陷盆地，发生了强烈的构造-沉积分异作用，形成了一套陆相-海-陆过渡相-海相的沉积体系。②四川盆地龙潭组富有机质层段可以划分为泥页岩夹灰岩型、砂泥灰互层型、泥页岩夹煤层型3种类型，分别形成于深水陆棚、浅水陆棚、潮坪-潟湖环境。③川东北地区二叠系龙潭组页岩沉积时古水深大，沉积水体滞留严重，封闭性和还原性增强，是有机质富集的理想场所。该区不仅具有下三叠统膏盐岩优质区域盖层，而且具备良好的顶板（长兴组灰岩）和底板（茅口组灰岩）条件，保存条件总体较好。④川东北地区龙潭组泥页岩具有“高有机碳含量（TOC>2%）、高热演化程度（R_o>2%）、高孔隙度（Φ>5%）、高石英含量（>40%）、高含气量（解吸气含量>3 m³/t）、高压力系数（~1.5）”六高特征，具有良好的页岩气赋存条件和资源潜力。⑤四川盆地二叠系龙潭组与五峰组-龙马溪组、Barnett、Ohio、Antrim、New Albany等国内外典型海相页岩类似，具备形成规模性页岩气赋存的良好地质条件，有望在埋深相对较浅、硅质页岩厚度较大的川东北-川东地区率先获得战略性突破。

Differential occurence of shale gas in the Permian Longtan Formation of Upper Yangtze region constrained by plate tectonics in the Tethyan domain

Great success has been achieved in marine shale gas exploration and development worldwide.Exploration in marine-terrestrial transitional and terrestrial shales has also been active in China but a large scale commercial development is yet to come.Based on the analysis of the controlling effect of the Permian plate tectonics on the formation and distribution of prototype basins and organic-rich shales in South China, we explored the petrographic, geochemical and mineral assemblages as well as reservoir characteristics of the Longtan Formation shale in the Sichuan Basin.In comparison to typical shale formations of similar sedimentary settings that are under commercial development elsewhere, we clarified the occurrence features and resource prospect of marine shale gas in the formation.The main conclusions are as follows: (1) Under the influence of the subduction of the Qinling and Jinshajiang (ocean) blocks and other tectonic events such as the Emei taphrogeny, multiple rift basins were developed in both the center and edge of the Yangtze platform and a set of continental-transitional-marine sedimentary system was also deposited by the subsequent intensive tectonic-sedimentary differentiation.(2) The organic-rich Longtan Formation in the Sichuan Basin can be lithologically categorized into three types: the mud-shale intercalated with limestone intervals of deep-water shelf facies, sandstone-mudstone-limestone interbeds of shallow-water shelf facies and mud-shale intercalated with coal beds of tide flat-lagoon facies.(3) The Longtan Formation in northeastern Sichuan Basin that was deep in stagnant water with good sealing and reducing properties during the Permian provided an ideal place for organic matter enrichment.In terms of preservation, the formation was not only confined by the regional Lower Triassic gypsolyte cap rocks, but also perfectly clamped between the Changxing Formation limestone (on top) and the Maokou Formation limestone (at the bottom).(4) The high organic carbon content (TOC>2%), thermal evolution maturity (R_o>2%), porosity (Φ>5%), quartz content (>40%), gas content (desorption gas content>3 m³/t), and high pressure coefficient (about 1.5) of the formation indicate favorable conditions for shale gas generation.(5) The Longtan Formation, similar to such typical marine shales as the Wufeng-Longmaxi Formations in the same basin, or as the Barnett, Ohio, Antrim and New Albany shales in the U.S., is geographically favorable to the generation of large-scale shale gas deposits.It is expected to take the lead in making strategic shale gas exploration breakthroughs, especially in the northeastern and eastern parts of the basin where the burial depth is relatively shallow and the siliceous shale is relatively thick.