页岩岩相组合划分标准及其对缝网形成的影响——以四川盆地志留系龙马溪组页岩为例

Division of shale lithofacies associations and their impact on fracture network formation in the Silurian Longmaxi Formation, Sichuan Basin

沈骋 任岚 赵金洲 陈铭培

Cheng Shen Lan Ren Jinzhou Zhao Mingpei Chen

页岩气储层需通过水力压裂实现经济产能，但不同页岩岩相组合类型具有不同的压裂改造效果。综合考虑矿物组分、储层物性、层理缝和层理对缝网形成的影响，结合露头、岩心发育特征和压裂改造特征，以四川盆地志留系龙马溪组页岩为研究对象，建立了Ⅰ型(FA1)、Ⅱ型(FA2)、Ⅲ型(FA3)和Ⅳ型(FA4)共4类页岩相组合划分标准。研究表明，FA1受明显成岩改造，胶结充填裂缝极为发育，压裂前期可优先激活形成缝网，但易发生压裂施工异常，导致裂缝扩展受限；FA2受沉积作用控制明显，易形成优势储集层与优势可压裂层的高密度交互；FA3和FA4受陆源物质影响较大，被改造能力较差，对缝网形成的促进作用不明显。总体上，FA1与FA2岩相组合是压裂施工的甜点。研究成果对储层压裂改造选井选层和压裂方案设计具有理论支撑和现场指导意义。

A commercial development of shale gas reservoirs largely depends on the effect of hydraulic fracturing.However, shale of different lithofacies associations responds differently to the treatment.The study used the Silurian Longmaxi Formation shale in the Sichuan Basin as an example to conduct a division of lithofacies associations and an analysis on the impact of the associations upon fracture networks.The roles of mineral composition, physical properties, beddings and bedding-parallel fractures of the shale in the formation of fracture networks were analyzed and then integrated with characterization of crops, cores and stimulation effect of hydraulic fracturing in the shale to define the association divisions.The results show that there are four types of lithofacies associations in the shale.Type Ⅰ association (FA1) is obviously the result of diagenesis modification and contains well-developed calcite-filled fractures, which can be activated preferentially to generate fracture networks but are also likely to confine the expansion of fractures during the earlier stage of fracturing.Type Ⅱ (FA2) shows evident signs of sedimentary control and tends to contain interbeds of promising gas reservoirs with crackable reservoirs.Type Ⅲ (FA3) and Type Ⅵ (FA4) are dominated by terrigenous components in comparison and are difficult to crack to from fracture networks.In all, FA1 and FA2 are the potential sweet spots for fracturing.The study is of theoretical support and on-site guiding significance to target formation selection and scheme design in fracturing.

10.11743/ogg20210109