川东北地区下侏罗统自流井组大安寨段陆相页岩脆性特征及其控制因素

Brittleness features and controlling factors of continental shale from Da’anzhai Member of the Lower Jurassic Ziliujing Formation， northeastern Sichuan Basin

王濡岳 胡宗全 赖富强 刘粤蛟 邬忠虎 何建华 邹冠贵 王鹏威 李治昊

Ruyue WANG Zongquan HU Fuqiang LAI Yuejiao LIU Zhonghu WU Jianhua HE Guan’gui ZOU Pengwei WANG Zhihao LI

以川东北地区下侏罗统自流井组大安寨段页岩层系为研究对象，通过系统开展岩相与矿物组分、动态和静态岩石力学性质以及成岩作用等研究，明确了大安寨段不同夹层类型页岩的脆性特征及其控制因素。结果表明：①大安寨段陆相页岩层系内主要包括黏土质页岩、粉砂质页岩、介壳灰质黏土质页岩和介壳灰岩4种岩石类型，整体表现为高黏土矿物含量、碳酸盐矿物局部富集特征。长英质矿物以陆源碎屑来源为主，有机质丰度与黏土、长英质和碳酸盐矿物含量间相互关系复杂。②页岩脆性受矿物含量、矿物结构及其相互关系共同影响。大安寨段处于中成岩阶段，固结程度较低，长英质矿物对脆性影响弱于碳酸盐矿物。钙质介壳含量的增加导致动、静态岩石力学参数的差异，并降低了岩石破裂及裂缝扩展所需的能量消耗。③大安寨段夹层类型多样，矿物组成与结构复杂。夹层结构均一型页岩动、静态力学参数具有良好正相关性，夹层结构不均一型（介壳夹层）页岩动、静态杨氏弹性模量总体负相关。因此，应充分考虑岩性、夹层类型、岩石力学性质差异性和成岩作用等因素，建立侏罗系陆相页岩脆性与可压裂性评价体系。上述结论对深化复杂夹层类型陆相页岩油气储层脆性认识与地质-工程甜点评价具有重要参考意义。

The brittleness features and their controlling factors of shale are clarified based on the systematic study of lithofacies and mineral composition， dynamic and static rock mechanical properties， and diagenesis of the Da’anzhai Member of the Lower Jurassic Ziliujing Formation in the northeastern Sichuan Basin. The following results are obtained. First， the continental shale sequence of the Da’anzhai Member is mainly composed of clayey shale， silty shale， shell limy clayey shale and shell limestone， featuring high content of clayey minerals and local enrichment of carbonate minerals. The source of felsic minerals is mainly terrigenous detritus， and the correlations between the TOC， clay， felsic and carbonate minerals are complex. Second， the brittleness of shale strata is under a joint effect of mineral content， mineral architecture and their interactions. The Da’?anzhai Member is at the middle diagenetic stage， with a low degree of concretion， and its felsic mineral content has a weaker effect on brittleness compared with carbonate minerals. The increasing content of calcareous shells leads to differences in dynamic and static rock mechanical parameters and reduces the energy consumed for rock fracturing and fracture propagation as required. Third， the interbeds in the Da’anzhai Member are diverse in type and complicated in mineral composition and architecture. The dynamic and static mechanical parameters of shale with interbeds of homogeneous architecture are in good positive correlation， while those of shale with interbeds of heterogeneous architecture （i.e. shell interbed） are in negative correlation in terms of Young’s modulus. In all， factors such as lithology， interbed type， differences in rock mechanical properties， and diagenesis should be fully considered to establish an evaluation system for the brittleness and fracability of continental shale in the Jurassic. The conclusions achieved above are of important referential value to deepening the understanding of the brittleness and the evaluation of geological-engineering sweet spots of continental shale reservoirs with interbeds of complex types.

10.11743/ogg20230209