The characteristics of pore development of the Lower Cambrian organic⁃rich shale in Sichuan Basin and its periphery

  • Liang Xiong
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  • Exploration and Production Research Institute, SINOPEC Southwest Company, Chengdu 610041, China

Received date: 2019-03-06

  Revised date: 2019-04-25

  Online published: 2019-10-14

Highlights

Lower Cambrian organic-rich shale is widely distributed with great thickness in Sichuan Basin and its periphery, which is the significant replacing layer of shale gas exploration. Based on the shale cores from several key wells, this paper systematically investigated the pore types and structures of Lower Cambrian organic-rich shale using SEM and low pressure nitrogen adsorption, and discussed the main controlling factors of pore development of Lower Cambrian organic-rich shale. The results indicate that there are significant differences between Lower Cambrian organic-rich shale from different regions. The relationship between total organic carbon content (TOC) and porosity is complex due to the influences from thermal maturation and organic matter composition which controls the development of organic matter-hosted pores. The Lower Cambrian organic-rich shale has various pore structures. With increasing maturation, pore structure changes by micropore vanishing, and specific surface area and pore volume decrease. Therefore, thermal maturation is one of the most important parameters for shale gas exploration and assessment of the Lower Cambrian in Sichuan Basin and its periphery.

Cite this article

Liang Xiong . The characteristics of pore development of the Lower Cambrian organic⁃rich shale in Sichuan Basin and its periphery[J]. Natural Gas Geoscience, 2019 , 30(9) : 1319 -1331 . DOI: 10.11764/j.issn.1672-1926.2019.04.009

0 引言

继2009年我国开展南方页岩气选区评价以来,在四川盆地上奥陶统五峰组—下志留统龙马溪组获得了页岩气勘探开发的商业成功,陆续建立了涪陵页岩气田、长宁页岩气田和威远页岩气田,威荣、富顺—永川等页岩气田正在建设之中。相比之下,分布范围更广、厚度更大、有机碳含量更高的下寒武统页岩气勘探举步维艰,直到2016年在鄂西宜昌黄陵隆起周缘下寒武统水井沱组发现高含气页岩层,才证实下寒武统页岩气资源具有勘探开发潜力[1]。本文以四川盆地及周缘下寒武统页岩气勘探最新钻井资料分析结果为基础,系统研究了下寒武统富有机质页岩孔隙微观特征和孔隙结构,并探讨了孔隙发育的主控因素,希望能对准确评价四川盆地及周缘下寒武统页岩孔隙特征、揭示页岩气赋存形式提供参考与借鉴。

1 研究背景

早寒武世梅树村期—筇竹寺期,上扬子地区经历了大范围的海平面上升事件[2],围绕川中碳酸盐岩台地存在四川盆地西南裂陷区和盆地外东南部2个深水陆棚沉积中心[3,4,5],发育了一套海相黑色富有机质泥页岩层系。晚古生代,下寒武统富有机质泥页岩进入生油阶段,早三叠世至晚白垩世大量物质快速沉积导致下寒武统泥页岩埋深达到6 000~8 000m,早期生成的油大量裂解生气[6,7,8],是威远大型震旦系气藏的主力气源[9]。近几年,在威远周边开展的页岩气调查揭示下寒武统富有机质泥页岩仍然含有一些天然气,证实下寒武统富有机质泥页岩具有页岩气勘探前景[10,11,12]
本文以川西南裂陷区金页1井(JY1)和盆外黄页1井(HY1)、恩页1井(EY1)下寒武统富有机质泥页岩为研究对象(钻井位置见图1),旨在分析下寒武统富有机质页岩孔隙度、孔隙结构和扫描电镜下微观特征,明确孔隙发育的主要影响因素,为下寒武统页岩气勘探选区评价提供参考。
图1 四川盆地及周缘下寒武统钻井分布简图(据文献[5]修改)

Fig. 1 The distribution of wellbores of Lower Cambrian shale formation in Sichuan Basin and the periphery (modified from Ref.[5])

2 富有机质页岩基本特征

川西南裂陷区JY1井下寒武统筇竹寺组富有机质页岩沉积厚度较薄(约15m),有机碳含量介于1.0%~3.0%之间,平均为1.8%,等效镜质体反射率平均为2.9%。页岩层段矿物组成以黏土矿物和石英矿物为主,其中黏土含量介于43%~60%之间,石英含量介于22%~34%之间,碳酸盐含量小于10%(图2)。黏土质泥页岩中偶见黄铁矿化介形虫和胶结有孔虫化石,有机质多与黏土矿物混合形成凝絮状结构(图3),反映了JY1井筇竹寺组富有机质页岩形成于贫氧—缺氧的环境。
图2 JY1井下寒武统泥页岩储层特征综合剖面

Fig.2 The integrated profile of Lower Cambrian shale reservoir characterizations of Well JY1

图3 JY1井下寒武统页岩显微照片

Fig.3 The microphotographs of Lower Cambrian shale from Well JY1

盆外黔中HY1井下寒武统九门冲组富有机质页岩沉积厚度大(约50m),有机碳含量介于3.5%~7.5%之间,平均为5.54%,等效镜质体反射率平均为3.1%。页岩层段矿物组成以石英矿物和黏土矿物为主,其中石英含量介于30%~53%之间,黏土含量介于13%~37%之间。碳酸盐含量在底部高达29%,其他层段含量小于10%(图4),底部含灰硅质页岩中存在微生物席状结构和方解石化红藻化石(图5),上覆硅质页岩可能为硅质软泥成岩演化的结果,说明HY1井九门冲组沉积时经历了从氧化至还原环境的变迁,对应早寒武纪全球海平面上升事件。
图4 HY1井下寒武统泥页岩储层特征综合剖面

Fig.4 The integrated profile of Lower Cambrian shale reservoir characterizations of Well HY1

图5 HY1井下寒武统页岩显微照片

Fig.5 The microphotographs of Lower Cambrian shale from Well HY1

盆外鄂西EY1井下寒武统水井沱组富有机质页岩沉积厚度大(约100m),富有机质页岩层段夹2层TOC含量较低的薄层灰质泥岩(图6)。富有机质页岩有机碳含量介于3.0%~10.7%之间,平均为6.93%,等效镜质体反射率平均为4.8%。页岩矿物组成以石英矿物和黏土矿物为主,其中石英含量介于24%~65%之间,黏土含量介于3%~30%之间,碳酸盐含量介于2%~20%之间,薄层灰质泥岩有机碳含量小于2.5%,平均为1.75%,黏土含量平均为53%,碳酸盐含量平均为41%,石英含量平均为4%。富有机质页岩存在硅质生物碎屑(图7),同时存在少量的金红石矿物,暗示硅质兼有生物来源和陆源碎屑输入。
图6 EY1井下寒武统页岩储层特征综合剖面

Fig.6 The integrated profile of Lower Cambrian shale reservoir characterizations of Well EY1

图7 EY1井下寒武统页岩显微照片

Fig.7 The microphotographs of Lower Cambrian shale from Well EY1

根据刘忠宝等[5]研究,JY1井筇竹寺组富有机质页岩形成于泥砂质浅水陆棚发生拉张裂陷作用时沉积水体迅速变深产生较深水浊积砂岩沉积,HY1井九门冲组富有机质硅质页岩形成于深水陆棚至斜坡缺氧环境,EY1井水井沱组富有机质页岩形成于炭泥质深水陆棚,由于古地理上靠近灰泥质浅水陆棚,沉积水体的小幅波动导致富有机质页岩沉积不如HY1井稳定。

3 孔隙发育特征

3.1 孔隙度

JY1井筇竹寺组富有机质泥质页岩氦气孔隙度介于3.58%~5.42%之间,平均为4.69%(图2),HY1井九门冲组富有机质硅质页岩氦气孔隙度介于1.09%~4.36%之间,平均为2.28%(图4),EY1井水井沱组富有机质硅质页岩氦气孔隙度介于0.17%~2.98%之间,平均为1.01%,薄层灰质泥岩孔隙度较硅质页岩好,平均为2.5%(图6)。

3.2 孔隙类型

通过场发射扫描电镜观察发现,JY1井筇竹寺组富有机质泥质页岩主要发育有机质孔和黏土矿物晶间孔(图8)。有机质孔普遍存在于充填有机质和残余原生有机质内部,孔径小于50nm,相比龙马溪组有机质孔孔径偏小。充填有机质分布于黄铁矿晶间、石英或黏土矿物骨架之间,与龙马溪组充填有机质具有相同特征,这些充填有机质内普遍发育良好的纳米级孔隙[图8(a), 图8(b)],其岩相学特征说明干酪根初次生烃产生的液态烃类滞留在或运移至基质骨架孔中,随后经历更强烈的热蚀变效应形成具有多孔的焦沥青[13,14,15]。黏土矿物晶间孔存在未被有机质充填的现象[图8(d)],说明这些晶间孔可能是孤立的,另外,有机质含量偏低而黏土矿物含量高(TOC含量平均为1.8%,黏土含量平均为51%)可能导致产生的次生有机质不够充填所有的黏土矿物晶间孔。
图8 JY1井筇竹寺组富有机质泥质页岩SEM微观特征

(a)充填于黄铁矿晶间有机质发育海绵状孔隙, 3 288.46m ,50 000×;(b)充填于石英矿物骨架间有机质发育海绵状孔, 3 290.23m,50 000×;(c)残余原生有机质内发育许多微小孔隙, 3 296.8m, 120 000×;(d)黏土矿物晶间孔未被有机质充填,与黏土矿物共存的有机质发育海绵状孔隙, 3 296.8m,25 000×

Fig.8 SEM characterization of organic-rich Qiongzhusi Formation shale from Well JY1

HY1井九门冲组富有机质硅质页岩有机质大致可分为残余原生有机质和充填次生有机质2种,残余原生有机质一般呈条带状或大型块状[图9(a)],一般内部不发育孔隙[图9(b)],充填次生有机质分布于石英和黏土矿物骨架之间,普遍发育海绵状孔隙[图9(c),图9(d)],孔径小于50nm。硅质页岩X-射线谱图与龙马溪组底部硅质页岩相似,硅质为微晶石英颗粒,粒径小且具棱角[图9(d)],说明HY1井九门冲组富有机质页岩的硅质来源于生物硅的成岩转化。除普遍存在的有机质孔之外,硅质矿物发育较多的粒内孔隙[图9(c),图9(d)],零星分布,孔径一般小于100nm。
图9 HY1井九门冲组富有机质硅质页岩SEM微观特征

(a)10 000×,2 388m,条带状残余原生有机质(红箭头)不发育孔隙,充填状次生有机质(黄箭头)发育海绵状孔隙;(b)65 000×,2 388m,残余原生有机质放大,不发育孔隙;(c)120 000×,2 398m,充填于矿物骨架间的有机质发育海绵状孔隙,石英矿物发育粒内孔;(d)65 000×,2 406m,充填于石英矿物骨架间的有机质发育海绵状孔隙,石英矿物发育粒内孔

Fig.9 SEM characterization of organic-rich Jiumenchong Formation shale from Well HY1

EY1井水井沱组富有机质页岩黏土矿物平均含量仅为13%,石英矿物平均含量为50%,石英颗粒与HY1井九门冲组硅质页岩具有相似的特征,可能暗示硅质来源系生物成因。有机质呈块状或充填状分布于石英矿物骨架之间,扫描电镜观察有机质孔隙发育差,无论是原生有机质残余还是充填状次生有机质,超过60%的有机质颗粒基本不发育孔隙(图10)。SEM观察到的有机质孔一般孔径较小,与JY1井和HY1井有机质孔相当,孔径稍大的孔隙呈不规则形态,有机质孔发育密度明显差于JY1井和HY1井富有机质页岩[图10(b)]。薄层灰质泥岩中的有机质充填于矿物基质空隙中[图11(a)],它们来源于上下富有机质页岩早期生成烃类的运移富集,充填有机质中普遍发育海绵状孔隙,孔径小于100nm[图11(b)]。
图10 EY1井水井沱组富有机质硅质页岩SEM微观特征

(a)25 000×,3 822m,充填于石英矿物骨架间有机质基本不发育孔隙;(b)20 000×,3 845m,有机质发育不规则形态的孔隙,孔径分布不均;(c)80 000×,3 890m,有机质零星发育少量孔隙,孔径较小;(d)7 000×,3 912m,充填于石英矿物骨架间有机质不发育孔隙

Fig.10 SEM characterization of organic-rich siliceous shale of Shuijingtuo Formation from Well EY1

图11 EY1井水井沱组灰质泥岩SEM微观特征

(a)1 200×,3 857.85m,有机质充填于矿物基质中,浅灰色为黏土,深灰色为方解石,黑色为有机质;(b)80 000×,3 877.08m,充填有机质发育海绵状孔隙,孔径小于100nm

Fig.11 SEM characterization of limy mudrock of Shuijingtuo Formation from Well EY1

3.3 孔隙结构

选用下寒武统富有机质页岩40~60目颗粒样品开展低压氮气吸附脱附实验,不同区域样品的氮气吸附脱附曲线存在显著的差异,暗示下寒武统页岩存在多样的孔隙结构。JY1井和HY1井下寒武统富有机质页岩的氮气吸附脱附曲线具有相似的特征,明显的迟滞现象且高压阶段没有吸附饱和平台(图12),说明页岩同时含有介孔和宏孔[16]。另外,低压阶段(P/P 0<0.01)较大的吸附量说明富有机质页岩含有一定量的微孔。EY1井下寒武统富有机质页岩的氮气吸附曲线与脱附曲线基本重合,高压阶段没有吸附饱和平台,且最大吸附量低,低压阶段(P/P 0<0.01)无吸附数据(图12),暗示EY1井富有机质页岩孔隙发育较差且以宏孔为主,不含氮气能有效进入的微孔[14]。JY1井和HY1井富有机质页岩最大吸附量介于5.9~14.2cm3/g之间,EY1井富有机质页岩最大吸附量小于5.4cm3/g,说明JY1井和HY1井富有机质页岩孔隙体积明显高于EY1井。
图12 下寒武统富有机质页岩氮气吸附—脱附曲线

Fig.12 Nitrogen adsorption/desorption curves of Lower Cambrian organic-rich shale

3.4 比表面积和孔容

基于低压氮气吸附曲线,采用BET方程计算[17]页岩的比表面积,T图法计算[18,19]微孔孔容和非微孔比表面积。微孔可以进一步分为极微孔(孔径<0.7nm)和次微孔(孔径介于0.7~2nm之间)[20],当多孔介质存在较多的极微孔时,氮气吸附未能检测到极微孔的存在,导致评价结果显著低于真实情况,此时二氧化碳吸附更具优势[21]。因此,本文采用T图法获得的微孔孔容为次微孔孔容,表1列出了下寒武统富有机质页岩比表面积和孔容分析数据。JY1井和HY1井富有机质页岩总孔容较大,次微孔孔容贡献为1/3,EY1井富有机质页岩总孔容较低,且不含次微孔,总孔容与孔隙度数据相吻合。JY1井和HY1井下寒武统页岩比表面积较大,TOC含量较高的HY1井富有机质页岩具有更大的比表面积,微孔不发育的EY1井富有机质页岩比表面积很小。从JY1井和HY1井富有机质页岩比表面积来看,微孔对比表面积的贡献超过50%,最高达90%以上。
表1 下寒武统富有机质页岩比表面积和孔容数据

Table 1 Specific surface areas and pore volumes of Lower Cambrian organic-rich shale

井号 深度/m

TOC

/%

总孔容

/(cm3/100g)

非微孔孔容

/(cm3/100g)

微孔孔容

/(cm3/100g)

比表面积

/(m2/g)

非微孔比表面积

/(m2/g)

微孔比表面积

/(m2/g)

JY1 3 288.95 1.00 1.12 0.73 0.39 11.59 1.71 9.88
3 290.8 1.56 0.94 0.48 0.45 13.37 1.81 11.56
3 292.1 1.25 1.00 0.65 0.35 11.41 2.87 8.55
3 296.8 3.01 1.85 1.43 0.42 17.63 7.75 9.88
3 298.2 2.10 0.91 0.39 0.52 14.71 1.60 13.11
HY1 2 371 7.48 1.69 0.97 0.72 22.01 1.35 20.66
2 374 7.31 1.19 0.47 0.72 20.96 2.57 18.39
2 378 5.53 0.92 0.46 0.46 13.07 1.26 11.81
2 383 5.24 1.60 0.96 0.64 19.46 3.56 15.89
2 388 3.46 1.51 0.92 0.59 18.85 4.67 14.17
2 392 5.15 1.54 1.06 0.48 16.23 4.55 11.68
2 398 5.08 1.39 0.88 0.52 15.08 1.90 13.18
2 402 5.61 1.42 0.82 0.60 17.89 2.65 15.25
2 406 4.87 2.01 1.34 0.67 23.47 8.13 15.34
2 411 5.71 1.88 1.25 0.63 22.86 7.94 14.92
2 414 5.89 1.84 1.27 0.58 21.89 7.94 13.95
2 417 3.77 2.20 1.87 0.33 19.34 12.41 6.93
2 420.39 5.55 1.73 1.31 0.43 18.54 8.60 9.94
2 422.5 6.92 1.20 0.83 0.37 13.78 4.93 8.85
EY1 3 814.9 8.95 0.64 0.64 0 3.94 3.94 0
3 835.12 5.86 0.83 0.83 0 8.29 8.29 0
3 844.9 5.75 0.66 0.66 0 3.70 3.70 0
3 857.85 2.29 1.31 1.31 0 3.99 3.99 0
3 877.08 1.2 0.93 0.93 0 1.53 1.53 0
3 901.45 7.44 0.57 0.57 0 1.59 1.59 0

4 孔隙发育影响因素

4.1 孔隙度

对于四川盆地龙马溪组页岩而言,孔隙度与TOC含量具有很好的线性正相关性,表明有机孔是它的主要孔隙类型[22,23]。下寒武统页岩孔隙度与TOC含量的关系显得较为复杂(图13),成熟度接近的JY1井和HY1井下寒武统页岩孔隙度与TOC含量不存在线性正相关性,孔隙度随着TOC含量增加先增大而后减小(图13),JY1井页岩孔隙度主要受到有机质含量的控制。Marcellus页岩孔隙度与TOC含量的关系更清楚反映了两者之间的关系[24],高TOC含量意味着单位体积页岩中含有更多的有机质,而有机质的抗压实能力弱于矿物基质,导致相同条件下高TOC含量页岩压实效应强于低TOC含量页岩,孔隙度减小。另外,不同类型的有机质具有不同的孔隙发育特征[25,26],HY1井页岩残余原生有机质不发育孔隙(图9),虽然对TOC含量有贡献,但对孔隙度没有影响。
图13 下寒武统页岩孔隙度与TOC的关系

Fig.13 The relationship between porosity and TOC of Lower Cambrian shale

成熟度为4.8%的EY1井下寒武统页岩孔隙度低于TOC含量相近但成熟度较低的HY1井下寒武统页岩(图13),含有相同TOC含量的低成熟度Marcellus页岩孔隙度高于高成熟度页岩[24],高温高压模拟实验说明进入高—过成熟阶段后页岩孔隙度随模拟条件的进一步升高而降低[27],张建坤等[28]指出成熟度为3.2%时有机质开始碳化,在压实作用下有机孔塌陷而减少,使得页岩孔隙度变小。
值得注意的是,下寒武统页岩孔隙度与黏土矿物含量存在一定的相关性(图14),主要与沉积环境和成岩演化有关。JY1井位于川西南裂陷区,大量陆源黏土碎屑的输入导致有机质与黏土形成絮状凝聚物,成岩演化适中,有机孔与黏土矿物骨架孔均发育(图8),因此孔隙度较好。HY1井和EY1井位于盆外被动大陆边缘,下寒武统页岩矿物组成相似,有机质来源与硅质生物相关,演化程度较低的HY1井富有机质页岩不管是有机质还是无机孔发育均好于演化程度较高的EY1井富有机质页岩(图9,10),相应地,HY1井页岩孔隙度好于EY1井页岩。
图14 下寒武统页岩孔隙度与黏土含量的关系

Fig.14 The relationship between porosity and clay mineral content of Lower Cambrian shale

相比龙马溪组页岩孔隙度主要受TOC含量控制,下寒武统页岩孔隙度与TOC含量、有机质组成、热成熟度等多因素相关,不同区域页岩孔隙度受控于不同的因素,需要区别研究。

4.2 比表面积与孔容

随着成熟度增加,有机质内微孔增多[29,30],同时微孔比表面积增大,因此TOC含量和成熟度是影响页岩比表面积的主要因素。四川盆地龙马溪组页岩TOC含量与比表面积具有正相关关系[22,31,32],北美主要页岩也具有相似关系[30]。对于下寒武统页岩,情况又变得复杂了。EY1井富有机质页岩比表面积显著低于JY1井和HY1井富有机质页岩[图15(a)],富有机质页岩不发育次微孔,说明过高的成熟度可能导致有机质不发育0.7~2nm微孔。当TOC含量小于5%时,比表面积随TOC含量线性增大[图15(a)],由于HY1井页岩不同程度地含有不发育孔隙的残余原生有机质,导致TOC含量大于5%时比表面积和TOC含量不存在明显相关性[图15(a)]。次微孔比表面积与TOC含量的关系[图15(b)]说明HY1井页岩虽然TOC含量高,但有机质贡献的次微孔比表面积却与JY1井相当,暗示HY1井页岩中不是所有的有机质都发育次微孔。因此,TOC含量、成熟度和有机质组成共同影响四川盆地下寒武统页岩比表面积的发育。
图15 下寒武统页岩比表面积和孔容与TOC含量的关系

Fig.15 The relationships between surface area and pore volume with TOC of Lower Cambrian shale

下寒武统页岩孔容与TOC含量之间表现出比表面积与TOC含量较相似的特征[图15(c)],EY1井页岩由于演化程度高,孔容普遍很小,高TOC含量页岩有机质对孔容的贡献基本相同,低TOC含量页岩有机质分散与矿物基质中,有机孔保持较好(图11),有机质对孔容的贡献反而较高。JY1井和HY1井页岩孔容随TOC含量先增大后减小,HY1井页岩残余原生有机质不发育孔隙,对孔容无贡献,导致TOC含量增加孔容反而减小。JY1井和HY1井页岩次微孔孔容基本相同[图15(d)],说明两者在相同的成熟度条件下发育次微孔的有机质含量相当。同样地,四川盆地下寒武统页岩孔容发育受到TOC含量、成熟度和有机质组成的共同制约。

4.3 有机孔

有机纳米孔隙对页岩气储集能力和渗流机理具有重要的影响意义,有机孔的结构特征显示它们形成于页岩中滞留烃类二次裂解生成气态烃的阶段[33,34,35,36],即有机孔的产生与热成熟度相关,形成于有机质裂解生气阶段[37]。针对Woodford页岩的研究认为有机孔的演化不仅与热成熟度有关,还受到其他因素的影响,如有机质组成[38],Bernard等[39]认为沥青组分在高成熟度条件下的二次裂解会形成含纳米孔隙的焦沥青。综合而言,热成熟度和有机质组成是影响有机孔发育的主要因素。
四川盆地下寒武统页岩热成熟度高,普遍处于过成熟阶段,有机质组成虽然相对简单,但经历了长期的热蚀变作用。JY1井和HY1井下寒武统页岩热成熟度接近,HY1井(EVRo=3.1%)略高于JY1井(EVRo=2.9%),EY1井下寒武统页岩热成熟度较高(EVRo=4.8%),长石种类主要为与低中级变质作用相关的钡长石。有机孔的发育与热成熟度密切相关,扫描电镜图像显示JY1井和HY1井下寒武统页岩有机质孔隙发育较好,而EY1井下寒武统页岩有机质孔隙发育较差(图8图10)。同时,不同有机质组分孔隙发育特征不同,有机孔主要发育在充填次生有机质中,而残余原生有机质具有不同的孔隙发育特征[图8(c), 图9(b)], 可能与母源类型有关。热成熟度升高,有机质内产生微孔[29,30],氮气吸附实验结果(图12,表1)表明EY1井下寒武统页岩不发育0.7~2nm微孔,说明有机质微孔的形成是具有热成熟度上限的。不管是从扫描电镜微观观察还是从孔隙结构特征来考虑,EY1井下寒武统页岩所处的热成熟阶段可能达到了有机孔消亡的门限。

5 结论

(1)不同地区下寒武统页岩孔隙度差异大,与TOC含量不存在简单的正相关关系,受到TOC含量、有机质组成、热成熟度等多因素的影响,超过热成熟度上限,页岩孔隙度会逐渐减小。
(2)下寒武统富有机质页岩氮气吸附脱附曲线表明不同成熟度的页岩具有不同的孔隙结构,JY1井和HY1井富有机质页岩以微孔和介孔为主,EY1井富有机质页岩以宏孔为主。页岩比表面积和孔容同时受到TOC含量、热成熟度和有机质组成的影响。
(3)下寒武统富有机质页岩含有残余原生有机质和充填次生有机质,有机孔主要分布在充填次生有机质之中,超过热成熟度上限,有机孔不发育。有机孔的发育受到有机质组成与热成熟度的共同控制。
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