四川盆地龙马溪组页岩微裂缝发育的“甜点”效应与机制

系统认识和明确页岩“甜点”层段中有机质和脆性矿物促进微裂缝发育的效应和机制，对于提高水力压裂效率，促进页岩气增产稳产具有重要的工程实践意义。本文系统调研了国内外页岩中有机质和脆性矿物控制下的裂缝发育机理等的研究成果，结合数值模拟，对四川盆地龙马溪组页岩“甜点”层段中微裂缝发育的效应和机制进行了全面剖析和探究。研究结果表明：四川盆地龙马溪组页岩特殊的沉积背景为裂缝的发育提供了良好的物质基础。其中有机质的不同成熟度阶段、空间分布和形状、丰度和有机孔隙都在不同程度上控制着微裂缝的形成和发育。脆性矿物在岩石破坏过程中能量的高效转化和良好的脆性响应机制，促进了裂缝的复杂化。少量裂缝的发育还受控于有机质和脆性矿物接触的力学边界、有机酸的溶蚀以及脆性矿物的嵌入等相关效应与机制，进一步突显了裂缝成因的复杂化。由此，建议未来关于页岩储层的脆性评价工作向多元组分的精细化方向发展，同时注重微米—纳米尺度下有机质和脆性矿物力学性质的表征，对于促进并深化页岩破裂机理的认识具有一定的研究价值。

“Sweet spot”effect and mechanism of shale micro-fracture development in Longmaxi Formation,Sichuan Basin

The systematic understanding and clarification of the effect and mechanism of organicmatter and brittle minerals in the shale“sweet spot”layer to promote the development ofmicro-fractures have important engineering practical significance for improving the hydraulicfracturing efficiency and promoting the increase and stability of shale gas production. In thispaper, the research results of the origin and mechanism of fracture development under thecontrol of organic matter and brittle minerals in shale at home and abroad are systematicallyinvestigated. Based on this, combined with the numerical simulation test, this paper focuses onthe comprehensive analysis and exploration of the effect and mechanism of micro-fracturedevelopment in the “sweet spot” section of Longmaxi Formation shale in Sichuan Basin. Theresults show that the special sedimentary background of Sichuan Basin determines thesynchronous enrichment of organic matter and brittle minerals with the bottom, which providesa good material basis for the development of fractures. The formation and development ofmicrofractures are controlled by different maturity stages, spatial distribution and shape,abundance and organic pores of organic matter. In the process of rock failure, the energyconversion of brittle minerals and good brittle response mechanism promote the complexity offracture. The development of individual fractures is controlled by the mechanical boundary ofcontact between organic matter and brittle minerals, the dissolution of organic acids, and theembedding of brittle minerals, which further highlights the complexity of fracture genesis. It issuggested that the future work on shale brittleness evaluation should consider the developmentof multi-component refinement, and pay attention to the characterization of mechanicalproperties of organic matter and brittle minerals at the micro-nano scale, which has certainresearch value forpromoting and deepening the understanding ofshalefracture mechanism.