深层富有机质页岩孔隙结构分形特征及其地质意义——以四川盆地威远地区下志留统龙马溪组为例  

Fractal characteristics of organic-rich shale pore structure and its geological implications:A case study of the Lower Silurian Longmaxi Formation in the Weiyuan block,Sichuan Basin

作　　者：管全中 董大忠[2] 孙莎莎[2] 胡澜潇 漆麟 李冲达 陈诚 陈鑫 GUAN Quanzhong;DONG Dazhong;SUN Shasha;HU Lanxiao;QI Lin;LI Chongda;CHEN Cheng;CHEN Xin(Chengdu University of Technology,Chengdu,Sichuan 610059,China;PetroChina Research Institute of Petroleum Exploration and Development,Beijing 100083,China;Shale Gas Exploration and Development Project Manager Department,CNPC Chuanqing Drilling Engineering Co.,Ltd.,Chengdu,Sichuan 610051,China;CCDC Geological Exploration&Development Research Institute,Chengdu,Sichuan 610051,China)

机构地区：[1]成都理工大学 [2]中国石油勘探开发研究院 [3]中国石油集团川庆钻探工程有限公司页岩气勘探开发项目经理部 [4]中国石油集团川庆钻探工程有限公司地质勘探开发研究院

出　　处：《天然气工业》2024年第3期108-118,共11页Natural Gas Industry

基　　金：国家自然科学基金项目“深层页岩有机质力学稳定性及对有机质孔隙的保存机理”(编号:42202192);四川省自然科学基金项目“富氦页岩气藏氦气封闭机理研究——以四川盆地龙马溪组为例”;中国石油“十四五”重大专项“川南海相深层页岩气资源潜力及富集规律研究”(编号:2021DJ1901)。

摘　　要：与中、浅层页岩不同,四川盆地南部地区上奥陶统五峰组—下志留统龙马溪组深层富有机质页岩经历了复杂的成岩作用,发育不同的孔隙结构,影响页岩气的赋存状态。为了探讨深层富有机质页岩的孔隙结构、分形特征及其对页岩气富集的影响,以该盆地南部威远地区龙马溪组页岩为研究对象,综合运用有机碳分析、X射线衍射、高分辨率扫描电镜和低温氮气吸附等测试手段,定量表征研究区深层富有机质页岩储层的基础参数及其孔隙结构特征;并运用FHH分形理论,结合低温氮气吸附实验,计算页岩孔隙分形维数,讨论孔隙结构的影响因素及其地质意义。研究结果表明:(1)研究区龙马溪组深层页岩有机质含量(TOC)高,平均值为2.04%,石英等脆性矿物含量占38.00%~73.00%;(2)龙马溪组深层页岩储层普遍发育墨水瓶状有机孔、狭缝型或平板状无机孔等,BET比表面积介于1.252~28.676 m^(2)/g,BJH孔体积介于0.013 192~0.063 874 cm^(3)/g;(3)深层页岩孔隙分形具有明显的分段性,分形维数D_(2)>D_(1),孔隙结构受页岩组成控制,分形维数受控于比表面积和孔径,且与TOC密切相关;(4) LM1—LM3笔石带沉积的富有机质硅质页岩TOC高、分形维数D_(1)和D_(2)值大,介孔BET比表面积和BJH孔体积最大,既有较多的气体吸附位点赋存吸附气,又有良好的孔隙空间贮存游离气,是深层页岩气富集的“甜点段”。结论认为,综合页岩品质参数和分形维数特征可有效评价页岩气富集的“甜点段”,并对实现深层页岩气的增储上产具有现实的指导意义。Different from medium and shallow shales,the deep organic-rich shales from the Upper Ordovician Wufeng Formation to Lower Silurian Longmaxi Formation in the southern Sichuan Basin have experienced intricate diagenesis,resulting in diverse pore structures that have a significant impact on shale gas occurrence.To explore the pore structure of deep organic-rich shale and its fractal characteristics and impact on shale gas enrichment,this paper quantitatively characterizes the basic parameters and pore structures of deep organic-rich shale reservoirs in the Longmaxi Formation in the Weiyuan block,southern Sichuan Basin by means of organic carbon analysis,X-ray diffraction,high-resolution scanning electron microscopy and low-temperature nitrogen adsorption.Then,based on the Frenkel-Halsey-Hill (FHH) fractal theory and low-temperature nitrogen adsorption experiments,the pore fractal dimension of shale is calculated,and the influencing factors and geological significance of the pore structure are discussed.The results show that the deep shale samples of the Longmaxi Formation in the Weiyuan block have a high total organic carbon (TOC) content (averaging 2.04%) and contain brittle minerals such as quartz (accounting for 38.00%-73.00%).The deep shale reservoirs of the Longmaxi Formation universally develop inkpot-like organic pores and slot-type or tabulate inorganic pores,with a BET specific surface area of 1.252-28.676 m^(2)/g and a BJH pore volume of 0.013 192-0.063 874 cm^(3)/g.The pores in the deep shales present obviously segmented fractals,with the fractal dimension D_(2)>D_(1).The pore structure is controlled by the composition of shales,while the fractal dimension is controlled by the specific surface area and pore diameter,and is closely related to the TOC content.The organic-rich siliceous shales deposited in the LM1-LM3graptolite zones have a high TOC content,high fractal dimension D_(1) and D_(2) values,and the largest BET specific surface area and BJH pore volume of mesopores.Therefore,they have many gas ads

关 键 词：四川盆地 威远地区 下志留统龙马溪组 深层页岩 孔隙结构 分形特征 

分 类 号：TE122.23[石油与天然气工程—油气勘探]