四川盆地川西坳陷三叠系须家河组页岩有机孔演化及成因

2022年 43卷 第No.2期
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Evolution and genesis of organic pores in Triassic Xujiahe Formation shale, Western Sichuan Depression, Sichuan Basin
徐亮 杨威 姜振学 陈冬霞 王耀华 鲁健康 赵明珠 李兰
Liang Xu Wei Yang Zhenxue Jiang Dongxia Chen Yaohua Wang Jiankang Lu Mingzhu Zhao Lan Li
以川西坳陷须家河组陆相页岩为例,通过场发射扫描电镜与EDS能谱相结合的方法有效识别出固体沥青、镜质体和惰质体三大显微组分,以及油沥青、焦沥青、结构镜质体、无结构镜质体、镜屑体、丝质体、半丝质体、惰屑体、菌类体等显微亚组分。扫描电镜下不同类型有机质孔隙发育程度差异大,有机粘土复合体中的固体沥青孔隙最为发育,其次为单独片状分布的固体沥青,镜质体和惰质体孔隙发育较差,主要以残余原生孔隙为主。受显微组分生烃潜力差异的控制,从固体沥青、镜质体到惰质体,三者的碳元素质量百分比依次增大,生烃潜力依次变差,成孔能力也依次变差;受粘土矿物催化作用的控制,随着伊利石含量增加,粘土矿物的比催化活度增加,可促进伊利石附近的固体沥青大量发育孔隙。仿真地层热模拟实验表明,不同有机显微组分孔隙演化差异大:随成熟度增加,固体沥青发育大量蜂窝状孔隙,面孔率不断增大,后期由于生烃枯竭导致面孔率逐渐减小;而镜质体和惰质体的孔隙发育较差,其原生孔隙还随成熟度的增加迅速减少。但镜质体和惰质体中广泛发育的微裂缝连通了沥青孔和其他无机孔,形成了微观孔-缝网络系统,提高了页岩储层的储集和渗流能力。
Samples from non-marine organic rich shale in the Xujiahe Formation, Western Sichuan Depression, Sichuan Basin, were analyzed with field emission scanning electron microscope and EDS energy spectrum. Three maceral components, including solid bitumen, vitrinite and intertinite, as well as microscopic subcomponents such as oil bitumen, tar bitumen, structured vitrinite, unstructured vitrinite, detrital-vitrinite, fusinite, semi-fusinite, detrital-intertinite, and sclerotinite were identified in these organic-rich shale samples. The organic pores of different types vary greatly under scanning electron microscopy: the organic pores develop the best in solid bitumen in organoclay complex, well in individual solid bitumen flakes, and the worst in vitrinite and intertinite mainly with residual primary pores. Controlled by difference in hydrocarbon generation potential, the three macerals have their weight percentages of carbon increasing and hydrocarbon generation and pore-forming potential deteriorating successively from solid bitumen, vitrinite to intertinite. Higher content of illite means higher specific catalytic activity, which promotes the development of pores in solid bitumen near the illite. Thermal simulation experiments show that the pore evolution of different macerals varies greatly. With maturity increasing, solid bitumen responds differently from other two maceral groups, it develops a large number of honeycomb pores with increasing cross-sectional porosity, which later gradually decreases due to the exhaustion of hydrocarbon generation. Meanwhile vitrinite and intertinite develop less pores and have their primary pores decreasing rapidly. However, the widely developed microcracks in the latter two groups connect bituminous pores and other inorganic pores, forming a microscopic pore-fracture network and improving the storage and seepage capacity of shale reservoirs.
成孔能力; 显微组分; 孔隙非均质性; 孔隙演化; 页岩; 须家河组; 川西坳陷; 四川盆地;
pore-forming capacity; maceral; pore heterogeneity; pore evolution; shale; Xujiahe Formation; Western Si-chuan Depression; Sichuan Basin;
10.11743/ogg20220207