下寺湾地区延长组陆相页岩孔隙特征及影响因素

(1.陕西延长石油(集团)有限责任公司研究院,陕西 西安 710075; 2.陕西省陆相页岩气成藏与开发重点实验室,陕西 西安 710075)

地质资源与地质工程; 孔隙特征; 场发射扫描电镜; 孔隙类型; 孔径大小

Pore characteristics and influential factors on lacustrine shale in Yanchang Formation,Xiasiwan Area
WU Chen-hong1,2,ZHANG Li-xia1,GAO Chao1,2

(1.Research Institute of Shaanxi Yanchang Petroleum(Group)Corp.,Ltd.,Xi'an 710075,China; 2.Shaanxi Key Laboratory of Lacustrine Shale Gas Accumulation and Exploitation,Xi'an 710075,China)

geological resources and engineering; pore characteristics; field emission scanning electron microscopy; pore types; pore diameter

DOI: 10.13800/j.cnki.xakjdxxb.2018.0616

备注

鄂尔多斯盆地下寺湾地区陆相页岩孔隙类型多样,微观非均质性强,为研究该区延长组长7陆相页岩储层孔隙特征,文中通过岩心描述、薄片观察、场发射扫描电镜等直接观察技术手段,结合气体吸附、核磁共振等实测分析技术,对陆相页岩的孔隙类型、大小分布进行研究。研究结果表明:长7页岩孔隙类型包括无机粒间孔、无机粒内孔和有机孔3大类及残余粒间孔、溶蚀粒间孔、碎屑与黏土粒间孔、溶蚀粒内孔、黏土矿物晶间微孔、有机孔、微裂缝7个亚类。页岩孔径从0.3 nm至15 μm范围内均发育,孔径100 nm以下的微孔,以有机孔和黏土矿物晶间孔隙为主,占总孔孔体积的41%~73%; 孔径大于5 μm的孔隙,以溶蚀孔隙为主,占总孔孔体积的25%~55%,页岩中的孔体积主要是由大孔和微孔贡献最大,成因以溶蚀孔和有机孔为主。分析孔隙发育影响因素可知:长7页岩中大孔(孔径>10 μm)孔隙体积与黏土矿物(25%~60%)、方解石含量(0.6%~2.7%)具有负相关关系,黏土矿物和方解石含量的增加占据粒间孔隙空间,大孔孔隙体积与斜长石、石英含量具有正相关关系,微孔(孔径<100 nm)的体积与黏土矿物含量具有正相关性。有机质含量和热演化程度是控制有机孔体积的主要因素,在低热演化背景下(Tmax<460 ℃),有机孔体积随热成熟度增大而增高。

The pore types of the lacustrine shale are diverse and the microcosmic heterogeneity is strong in the Ordos Basin.In order to study the reservoir characteristics and its influence on lacustrine shale in Chang 7formation,Chang 7shales pore characteristics were studied by core and thin section observation,field emission scanning electron microscopy(FSEM)in combination with nitrogen isothermal adsorption experiments and NMR core analysis.It is pointed that pore types of Chang 7shale are residual intergranular pore,dissolution intergranular pore,debris and clay intergranular pore,dissolution intragranular pore,intergranular micropore between clay minerals,organic pore and micro fracture,pores smaller than 100nm and greater than 5μm are most abundant.The pores with pore diameter below 100nm are mainly organic pore and clay mineral intergranular pores,accounting for 41%~73% of the total pore volume.Pores greater than 5μm are mainly in the dissolution of pores,accounting for 25%~55%.The pore volume in shale is mainly contributed by large pores and micro pores,which are mainly the dissolution and organic pores.The results indicate that the macropore(diameter>10μm)has a negative correlation with the amount of clay minerals(25%~60%)and calcites(0.6%~2.7%),with increase in their content taking up the intergranular pore space,and has a positive correlation with the amount of quartz and plagioclase.The micropore(diameter<100nm)has a positive correlation with the amount of clay minerals.The volume of organic pores is controlled by TOC and thermal maturity.At the background of low thermal evolution(Tmax< 460℃),organic pores developed more with the increase of thermal maturity.