文章快速检索     高级检索
  地质与资源 2021, Vol. 30 Issue (2): 143-152  
0
引用本文
谢志涛, 胡海燕, 袁浩莆, 刘冀蓬, 王涛, 刘立航. 页岩组分对五峰-龙马溪组与牛蹄塘组页岩孔隙发育差异的影响——以渝东南焦页1井与湘西北慈页1井为例[J]. 地质与资源, 2021, 30(2): 143-152.  
XIE Zhi-tao, HU Hai-yan, YUAN Hao-pu, LIU Ji-peng, WANG Tao, LIU Li-hang. INFLUENCE OF SHALE COMPONENTS ON THE PORE DEVELOPMENT DIFFERENCES BETWEEN WUFENG-LONGMAXI FORMATION AND NIUTITANG FORMATION: A Case Study of JY-1 Well in Southeast Chongqing and CY-1 Well in Northwest Hunan[J]. Geology and Resources, 2021, 30(2): 143-152.  

页岩组分对五峰-龙马溪组与牛蹄塘组页岩孔隙发育差异的影响——以渝东南焦页1井与湘西北慈页1井为例
谢志涛1 , 胡海燕2,3 , 袁浩莆4 , 刘冀蓬1 , 王涛1 , 刘立航1     
1. 长江大学 地球科学学院, 湖北 武汉 430100;
2. 长江大学 资源与环境学院, 湖北 武汉 430100;
3. 非常规油气湖北省协同创新中心, 湖北 武汉 430100;
4. 西部钻探工程有限公司地质研究院, 新疆 克拉玛依 834000
摘要:根据页岩样品不同孔径范围的累计孔体积与累计比表面积,结合焦页1井五峰-龙马溪组与慈页1井牛蹄塘组页岩样品的地球化学参数与岩样各矿物组分百分含量,分析页岩组分对两套地层孔隙发育差异的影响.结果显示,TOC与微孔呈正相关关系,表明有机质微孔对页岩孔隙发育提供了一定的贡献,五峰-龙马溪组页岩较牛蹄塘组更为发育有机质微孔.石英、黄铁矿含量与微孔的正相关关系表明,矿物支撑的原生孔与发育的边缘孔为页岩孔隙发育提供了有利贡献.石英与中孔、大孔的不同相关性表明石英根据其生物成因贡献的石英含量对中孔、大孔的保护程度不一.黄铁矿含量与大孔的正相关关系表明黄铁矿可以根据其含量的多寡为大孔提供一定程度的保护,长石与孔隙的负相关关系表明其对孔隙的支撑作用受到了压实作用、复杂构造的影响而不明显.碳酸盐矿物与孔隙的相关性不明显表示基于其较弱刚性、不稳的化学性质与较低含量未对孔隙发育产生明显影响.五峰-龙马溪组页岩较高的刚性矿物含量对储层矿物粒间孔、边缘孔等微孔与中孔、大孔的发育起到了较牛蹄塘组更为有利的影响.黏土矿物与微孔、中孔的负相关关系表明在较强压实作用下黏土矿物间孔隙易收缩,对储层孔隙发育产生不利影响,表明牛蹄塘组经历的更深历史埋藏对牛蹄塘组黏土矿物间孔隙发育起到了更加不利的影响.
关键词五峰-龙马溪组    牛蹄塘组    有机碳含量    页岩    孔隙    中上扬子地区    
中图分类号:P618.13            文献标志码:A             文章编号:1671-1947(2021)02-0143-10
INFLUENCE OF SHALE COMPONENTS ON THE PORE DEVELOPMENT DIFFERENCES BETWEEN WUFENG-LONGMAXI FORMATION AND NIUTITANG FORMATION: A Case Study of JY-1 Well in Southeast Chongqing and CY-1 Well in Northwest Hunan
XIE Zhi-tao1 , HU Hai-yan2,3 , YUAN Hao-pu4 , LIU Ji-peng1 , WANG Tao1 , LIU Li-hang1     
1. School of Geosciences, Yangtze University, Wuhan 430100, China;
2. School of Resources and Environment, Yangtze University, Wuhan 430100, China;
3. Hubei Cooperative Innovation Center of Unconventional Oil and Gas, Yangtze University, Wuhan 430100, China;
4. Xibu Drilling Engineering Co., Ltd., CNPC, Karamay 834000, Xingjian Autonomous Region, China
Abstract: Based on the accumulative pore volume and specific surface area by pore diameter of shale samples from JY-1 well of Wufeng-Longmaxi Formation and CY-1 well of Niutitang Formation, combined with the geochemical parameters and percentage of mineral components in samples, the paper analyzes the influence of shale components on the pore development differences between the two formations. The results show that TOC is positively correlated with micropores, indicating the organic micropores contribute to the development of shale pores, and organic micropores are more developed in the shale of Wufeng-Longmaxi Formation than that in Niutitang Formation. The positive correlation between quartz-pyrite contents and micropores indicates the primary pores and developed marginal pores contribute to the development of shale pores. The different correlations between quartz and meso-and macropores reveal the different protection degrees of quartz to the two by biogenic quartz content. The positive correlation between pyrite content and macropores reflects that pyrite can protect macropores to a certain extent in terms of pyrite content. The negative correlation between feldspar and pores shows the less obvious support of feldspar on pores due to the influence of compaction and complex structure. The unobvious correlation between carbonate minerals and pores shows the weak rigidity and instability of chemical properties and low content have no significant influence on pore development. Compared with Niutitang Formation, the high content of rigid minerals in the shale of Wufeng-Longmaxi Formation has a more favorable influence on the development of micropores (such as intergranular and marginal pores), mesopores and macropores. The negative correlations between clay minerals and micro- and mesopores indicate the intermineral pores easy to shrink under strong compaction have a negative effect on the pore development of reservoir, reflecting that the deep burial of Niutitang Formation has an unfavorable effect on the development of intermineral pores.
Key words: Wufeng-Longmaxi Formation    Niutitang Formation    TOC    shale    pore    middle-lower Yangtze Valley area    

0 引言

近年来,随着我国南方海相页岩气勘探研究工作的深入,广泛发育着富含有机质的上奥陶统五峰组-下志留统龙马溪组、下寒武统牛蹄塘组(筇竹寺组、水井沱组)的中上扬子地区已成为页岩气勘探开发的热点地区[1-4]. 但目前只有五峰-龙马溪组页岩储层进入了工业性开发阶段,牛蹄塘组页岩仍处于勘探研究阶段[5]. 作为中上扬子地区最具潜力的两套页岩气层,研究页岩组分对五峰-龙马溪组与牛蹄塘组页岩孔隙发育的影响,并以此选择针对性方案来指导牛蹄塘组页岩气勘探开发,则是未来的工作中的关键问题. 为此,本文综合钻测井资料、地球化学实验与X射线全矿物衍射数据,分析页岩各组分对焦页1井五峰-龙马溪组与慈页1井牛蹄塘组页岩孔隙发育的影响,研究造成页岩孔隙差异的组分,以期为牛蹄塘组页岩气勘探开发提供依据.

1 区域地质特征

中上扬子地区隶属于华南地区扬子地层区与江南分区,东与华夏地块相接,西与龙门山构造带、松潘甘孜造山带、三江造山带相连,北至秦岭-大别山构造带与华北陆块连接,南到湘黔贵地块桂中凹陷[6]. 先后发生的加里东运动、印支运动、燕山运动、喜马拉雅运动等4次强烈的构造运动,造成了中上扬子地区多期次、多样式的复杂陆内复合构造系统(图 1a).

图 1 研究区地质构造与沉积相图(据文献[6-7, 9]) Fig.1 Tectonic and sedimentary facies maps of the study area(From References [6-7, 9]) a一中上扬子地区地质构造(lectonics of mitlle-upper YangtreValley area); b一四川盆地及其周缘五蜂-龙马溪组岩相古地理(lithofacies paleogeography of Wiufeng-Longmani fm.in Sichuan Basin and peripheral; c一湘西北牛蹄塘组岩相古地理(lithofacies paleogeography of Niuitang fm. innorthwest Hunman); 1—一级构造单元(frst-onler tectonic unit; 2—二级构造单元(second-order teconic unit); 3—三级构造单元(thir-order fectonicunit); 4一断层(fault); 5—盆地边界(hasin boundary); 6一相边界(facies boundary); 7—页岩厚度等值线(isoline of shale thickness); 8一目的井(target well); 9—城市(city)

渝东南研究区位于八面山隔挡构造带内. 焦页1井目的层五峰-龙马溪组在低能、欠补偿、缺氧的局限海域沉积环境中发育一套大规模海相页岩,五峰-龙马溪组自下而上由深水陆棚沉积环境过渡到浅水陆棚沉积环境[7-8](图 1b).

湘西北研究区位于雪峰基底隆升构造带内. 慈页1井目的层牛蹄塘组在低能、缺氧的还原环境中沉积了一套夹黑色硅质岩、石煤、磷结核的富有机质页岩,炭质含量较高[9-10](图 1c).

2 样品选取

渝东南焦石坝地区目的层段五峰-龙马溪组是目前我国最为优质的页岩气储层[11-12]. 焦页1井在五峰-龙马溪组进尺88.00 m (2327.00~2415.00 m),取心84.77 m,自下而上划分为9个小层[13-14]. 通过对焦页1井五峰-龙马溪组中8个小层取样. 获得12个页岩样品,根据中石化勘探分公司的页岩样品实验分析:总有机碳含量(TOC) 0.53%~6.45%,平均2.66%,下部深水陆棚相有机质泥页岩有机碳含量较高,基本大于平均值;镜质体反射率(Ro) 2.20%~3.13%,平均2.65%,属于过成熟演化阶段. 根据中石化勘探分公司的全矿物衍射分析(X射线衍射)实验:石英含量27.02%~48.43%,钾长石1.41%~5.77%,斜长石5.75%~11.82%,方解石0~12.27%,白云石0~10.63%,黄铁矿2.70%~5.13%,黏土矿物含量27.04%~54.12% (图 2a). 12个样品中,6个为浅水陆棚相样品,6个为深水陆棚相样品. 其中2个属于含硅黏土质页岩相,3个属于含黏土/硅混合质页岩相,7个属于含黏土硅质页岩相,基本涵盖目的层段五峰-龙马溪组页岩岩相类型,符合对比评价标准.

图 2 研究区页岩样品全矿物含量 Fig.2 Total mineral contents of shale samples in the study area a一焦页1井页岩样品(shale samples of JY-1 well; b一慈页1井页岩样品(shale sample of C'Y-1 wl); 1一黏土矿物(clay mineral; 2一黄铁矿(pyrite); 3一白云石(dolomie); 4一方解石(calcite); 5一斜长石(plagioclase); 6一钾长石(potash feldspar); 7一石英(quartz)

湘西北慈利地区目的层牛蹄塘组是中上扬子地区另一套分布广泛的富有机质海相页岩,其页岩气参数井——慈页1井在下寒武统牛蹄塘组地层钻遇良好气显示段81 m,在2264.42~2827.64 m井段取心97.30 m. 通过对慈页1井牛蹄塘组4个小层取样,获得8个样品,根据中石化勘探分公司的页岩样品实验分析:TOC含量1.70%~6.19%,平均2.46%;镜质体反射率平均3.42%,达到过成熟演化阶段. 与五峰-龙马溪组相似,总有机碳含量随深度增加而增加. 根据中石化勘探分公司的全矿物衍射分析(X射线衍射)实验:石英含量38.93%~68.21%,钾长石0.86%~9.92%,斜长石2.86%~12.04%,方解石0~3.10%,白云石1.98%~8.92%,黄铁矿0.88%~4.10%,黏土矿物含量14.82%~40.97% (图 2b). 8个样品中,主要沉积环境为缺氧还原环境,其中5个属于含黏土硅质页岩相,2个属于混合硅质页岩相,1个属于硅质页岩相,基本涵盖目的层段牛蹄塘组页岩岩相类型,符合对比评价标准.

3 五峰-龙马溪组与牛蹄塘组页岩孔隙差异化影响因素

将样品研磨至60~80目进行筛选,110 ℃条件下抽真空,持续脱气12 h,然后通过0 ℃下CO2吸附、-196.15 ℃(77 K) N2吸附、高压压汞实验,借助非定域密度函数方程、骤冷固体密度函数方程、Washburn-Yong-Duper方程,计算目的层样品的全孔径分布曲线,利用数学方法微分曲线获得目的层样品的累计孔体积与累计比表面积数据[15-18] (图 3). 结果显示,焦页1井五峰-龙马溪组页岩样品中大孔体积分数最大,中孔次之,微孔最小,平均总孔体积在37.04×10-3 cm3/g;而慈页1井牛蹄塘组页岩样品则以微孔、中孔体积为主,大孔的体积分数最低,平均总孔体积在10.33×10-3 cm3/g. 五峰-龙马溪组页岩孔隙比表面积以微孔为主,中孔次之,大孔的比表面积最小,平均总孔比表面积在22.90 m2/g;牛蹄塘组页岩孔隙比表面积同样以微孔为主,中孔、大孔比表面积依次降低,平均总孔比表面积为16.98 m2/g. 对比发现,牛蹄塘组页岩孔隙发育远低于五峰-龙马溪组,集中表现为大孔体积发育差异,这会影响牛蹄塘组气渗通道的连通性,但微孔的发育相差远小于中孔、大孔的差距. 从页岩气的赋存机理上看,页岩气吸附气主要赋存于微孔表面[19-20],五峰-龙马溪组微孔平均比表面积为15.25 m2/g,牛蹄塘组微孔平均比表面积为13.68 m2/g,表明牛蹄塘组较五峰-龙马溪组亦有充足的页岩气吸附空间. 钻井资料显示,牛蹄塘组历史埋藏更深,压实作用更加剧烈,这是影响牛蹄塘组孔隙发育的一个主要宏观因素. 有机质页岩中影响孔隙发育的因素有很多,除历史埋藏外还有页岩中的各组分,如TOC、矿物组分.

图 3 目的层页岩样品累计孔体积与累计孔比表面积 Fig.3 Accumulative pore volume and specific surface area of shale samples from farget layers a一焦页1井样品累计孔体积(accumulative pore volume of samples from JY-1 well); b一焦页1井样品累计孔比表面积(acumulative specific surarearea of samples from JY-1 well); c—慈页1井样品累计孔体积(accumulative pore volume of samples from CY-l wel); d一慈页1井样品累计孔比表面积(accumulative specific suface area of samples from C'Y-1 well); 1一微孔(micropore); 2—中孔(mesopore); 3—大孔(macropore)
3.1 TOC对页岩孔隙发育差异的影响

除个别样品外,五峰-龙马溪组页岩样品中,TOC与微孔、中孔总孔体积呈现出较强的明显正相关关系,与大孔总孔体积的相关性不明显;与微孔总孔比表面积、中孔总孔比表面积同样呈现出较强的明显正相关关系,与大孔总孔比表面积表现出较强的不明显正相关关系(图 4ab). 而牛蹄塘组页岩中TOC只与微孔总孔体积、微孔总孔比表面积有较强的明显正相关关系,与中孔、大孔之间的正相关性不明显(图 4cd). 这表明TOC对有机质页岩中的微孔发育有较好的促进作用,这是因为有机质在热解生烃过程中,由于有机质的消耗而形成有机质微孔的缘故[21-22]. TOC对五峰-龙马溪组与牛蹄塘组间孔隙差异的影响体现在微孔发育上,在均处于过成熟演化阶段条件下,五峰-龙马溪组页岩样品的TOC平均值为2.66%,略高于牛蹄塘组页岩样品的平均值2.46%,这是二者微孔发育差异的一个重要因素.

图 4 TOC与目的层样品孔隙的相关性分析 Fig.4 Correlation between 'TOC and sample pore of target layers a一TOC与五峰-龙马溪组样品总孔体积相关性(corelation between 'TOC and total pore volume of samples from Wufeng-Longmaxi fm.); b一TOC与五峰-龙马溪组样品总孔比表面积相关性(corelation between TOC and total pore specific surace area of samples from Wiufleng-Longmaxi fm); c—TOC与牛蹄塘组样品总孔体积相关性(eorrelation belween'TOC and total pore volume f saumples from Niutiang fm.); d一TOC与牛路塘组样品总孔比表面积相关性(correlation between 'TOC and total pore specific suface area of samples from Niutitang fm); 1一微孔(micropore); 2一中孔(mespore); 3一大孔(macrypore)
3.2 矿物组分对页岩孔隙发育差异的影响

页岩矿物受沉积环境与成岩过程的控制,组分繁复[23-24]. 通过全岩矿物X衍射分析,将样品中的矿物组分划分为石英、长石(钾长石、斜长石)、碳酸盐矿物(方解石、白云石)、黄铁矿等刚性矿物与黏土矿物等塑性矿物,分类进行分析.

3.2.1 石英

石英属于刚性矿物,在焦页1井五峰-龙马溪组样品中,除个别样品外,表现为与微孔、中孔的总孔体积、总孔比表面积有明显的正相关关系,与大孔总孔比表面积有不明显的正相关关系,与大孔的总孔体积相关性则不明显(图 5ab);在慈页1井牛蹄塘组样品中,除个别样品外,石英与微孔、大孔的总孔体积和微孔、中孔总孔比表面积表现为明显的正相关关系,而与中孔的总孔体积相关性不明显,与大孔总孔比表面积有不明显的正相关关系(图 5cd). 五峰-龙马溪组中石英含量与TOC有较明显的正相关关系,而牛蹄塘组与TOC的相关性极差(图 5q),这表明焦页1井中石英的生物成因贡献较大,而慈页1井中石英的生物成因贡献较小. 综上说明石英矿物对页岩中微孔的发育有一定的促进作用,这是因为同沉积石英矿物可以抑制压实过程对原生孔隙的压实强度,一定程度上保存原生孔隙,并发育颗粒边缘孔隙[25]. 而慈页1井与焦页1井中石英矿物含量与中孔、大孔发育的差异表明不同成因的石英矿物对孔隙发育的影响不同,非生物成因石英可能对大孔的发育更为有利. 五峰-龙马溪组样品中石英的平均含量为37.29%,略高于牛蹄塘组样品中34.90%的,且生物成因贡献的石英含量相对较多,更加有利于微孔、中孔的保护,这是造成牛蹄塘组微孔、中孔发育略差于五峰-龙马溪组的一个重要因素.

图 5 刚性矿物组分与目的层样品孔隙及TOC相关性分析 Fig.5 Correlation between rigid mineral components and sample pore of target layers a-石英含量与五峰-龙马溪组样品总孔体积相关性(quartz content vs. total pore volume of Wufeng-Longmaxi fm.);b-石英含量与五峰-马溪组样品总孔比表面积相关性(quartz content vs. total pore specific surface area of Wufeng-Longmaxi fm.);c-石英含量与牛蹄塘组样品总孔体积相关性(quartz content vs. total pore volume of Niutitang fm.);d-石英含量与牛蹄塘组样品总孔比表面积相关性(quartz content vs. total pore specific surface area of Niutitang fm.);e-长石含量与五峰-龙马溪组样品总孔体积相关性(feldspar content vs. total pore volume of Wufeng-Longmaxi fm.);f-长石含量与五峰-龙马溪组样品总孔比表面积相关性(feldspar content vs. total pore specific surface area of Wufeng-Longmaxi fm.);g-长石含量与牛蹄塘组样品总孔体积相关性(feldspar content vs. total pore volume of Niutitang fm.);h-长石含量与牛蹄塘组样品总孔比表面积相关性(feldspar content vs. total pore specific surface area of Niutitang fm.);i-碳酸盐矿物含量与五峰-龙马溪组样品总孔体积相关性(carbonate mineral content vs. total pore volume of Wufeng-Longmaxi fm.);j-碳酸盐矿物含量与五峰-龙马溪组样品总孔比表面积相关性(carbonate mineral content vs. total pore specific surface area of Wufeng-Longmaxi fm.);k-碳酸盐矿物含量与牛蹄塘组样品总孔体积相关性(carbonate mineral content vs. total pore volume of Niutitang fm.);l-碳酸盐矿物含量与牛蹄塘组样品总孔比表面积相关性(carbonate mineral content vs. total pore specific surface area of Niutitang fm.);m-黄铁矿含量与五峰-龙马溪组样品总孔体积相关性(pyrite content vs. total pore volume of Wufeng-Longmaxi fm.);n-黄铁矿含量与五峰-龙马溪组样品总孔比表面积相关性(pyrite content vs. total pore specific surface area of Wufeng-Longmaxi fm.);o-黄铁矿含量与牛蹄塘组样品总孔体积相关性(pyrite content vs. total pore volume of Niutitang fm.);p-黄铁矿含量与牛蹄塘组样品总孔比表面积相关性(pyrite content vs. total pore specific surface area of Niutitang fm.);q-TOC与焦页1井、慈页1井石英含量相关性(TOC vs. quartz content of shale samples from CY-1 and JY-1 wells);1-微孔(micropore);2-中孔(mesopore);3-大孔(macropore);4-焦页1井(JY-1 well);5-慈页1井(CY-1 well)
3.2.2 长石

长石(钾长石、斜长石)属于刚性矿物,同样在一定程度上起着抑制压实过程对原生孔隙破坏的作用. 在焦页1井五峰-龙马溪组样品中,表现为与微孔、中孔的总孔体积、总孔比表面积较明显的负相关关系,与大孔的总孔比表面积不明显的负相关关系,与大孔的总孔体积的相关性不明显(图 5ef);在慈页1井牛蹄塘组样品中,除个别样品外,表现为与中孔的总孔体积、总孔比表面积较明显的负相关性,与大孔的总孔比表面积有不明显的负相关关系,与微孔的总孔体积、总孔比表面积及大孔的总孔体积无明显相关性(图 5gh). 表明在这两套地层中,长石未起到保护孔隙的作用,这可能是因为在页岩样品中,随着长石相对含量的增加,黏土矿物的相对含量也在增加,且大于长石的增加量,而黏土矿物的易压实收缩孔隙强度强于长石对孔隙的保护强度,导致了微孔、中孔的总孔体积与总孔比表面积的降低. 五峰-龙马溪组样品中,钾长石平均含量为2.17%,斜长石平均含量为7.15%,略高于牛蹄塘组样品中钾长石的平均含量1.39%、斜长石平均含量6.67%,表明五峰-龙马溪组样品抵挡黏土矿物压实收缩孔隙影响的强度也略高于牛蹄塘组样品. 这是造成两套地层孔隙差异的另一因素.

3.2.3 碳酸盐矿物

碳酸盐矿物(方解石、白云石)属于脆性/刚性矿物. 在焦页1井五峰-龙马溪组样品中,表现为与微孔的总孔体积、总孔比表面积有明显的正相关关系,与中孔的总孔体积、总孔比表面积有较明显的正相关关系,与大孔的总孔比表面积有不明显的正相关关系,与大孔的总孔体积相关性则不明显(图 5ij);在慈页1井牛蹄塘组样品中,与微孔的相关性不明确,只与中孔、大孔的总孔比表面积有不明显的正相关关系(图 5kl). 这是因为碳酸盐矿物虽属脆性矿物,对孔隙起着一定程度的保护作用,但较于石英、长石颗粒来说稳定性弱,保护强度低,当含量较低时,这种保护作用则不明显. 这是影响五峰-龙马溪组与牛蹄塘组页岩孔隙差异的另一因素.

3.2.4 黄铁矿

黄铁矿属于刚性矿物,在焦页1井五峰-龙马溪组样品中,表现为与中孔的总孔体积有良好的明显正相关关系,与微孔、大孔的总孔体积有较差的正相关关系,与微孔、中孔的总孔比表面积有良好的正相关关系,与大孔的总孔比表面积有不明显的正相关性(图 5mn);在慈页1井牛蹄塘组样品中,除个别样品外,表现为与微孔、大孔的总孔体积和微孔的总孔比表面积有明显的正相关关系,与中孔的总孔体积、总孔比表面积无明显相关性(图 5op). 表明黄铁矿属于刚性矿物,对微孔、大孔的保护作用依然有效,在强压实作用下,可以有效地保护孔隙,但随着埋藏深度、压实强度的增加而减弱,随黄铁矿含量的降低而降低. 牛蹄塘组页岩中普遍低于五峰-龙马溪组的黄铁矿含量是造成其大孔弱发育的一个重要因素.

3.2.5 黏土矿物

黏土矿物是页岩中的重要矿物成分,尽管其所包含的矿物种类繁多,对矿物晶间与颗粒间孔隙的影响范围不尽相同,但共有特性依然存在,即强塑性. 黏土矿物只有在埋藏较浅,压实作用强度较小时,才能为储层孔隙发育提供一定的贡献. 在焦页1井五峰-龙马溪组样品中,黏土矿物表现为与微孔、中孔的总孔体积、总孔比表面积有明显的负相关关系,与大孔的总孔比表面积有不明显的负相关关系,与大孔的总孔体积相关性则不明显(图 6ab);在慈页1井牛蹄塘组样品中,表现为与微孔、中孔、大孔的总孔体积均有一定程度的负相关关系,与微孔、中孔总孔比表面积有明显的负相关关系,与大孔总孔比表面积有不明显的负相关关系(图 6cd). 表明黏土矿物对大孔的孔隙结构影响微弱,而蒙脱石、伊蒙混层形成的微孔与伊利石、绿泥石形成的微孔-中孔在较大埋深下由于黏土矿物较强塑性的缘故不能对储层孔隙提供有效贡献,这是造成两套地层微孔、中孔发育差异的重要因素.

图 6 黏土矿物含量与目的层样品孔隙相关性分析 Fig.6 Correlation between clay mineral content and sample pore of target layers a-黏土矿物含量与五峰-龙马溪组样品总孔体积相关性(correlation between clay mineral content and total pore volume of samples from Wufeng-Longmaxi fm.);b-黏土矿物含量与五峰-龙马溪组样品总孔比表面积相关性(correlation between clay mineral content and total pore specific surface area of samples from Wufeng-Longmaxi fm.);c-黏土矿物含量与牛蹄塘组样品总孔体积相关性(correlation between clay mineral content and total pore volume of samples from Niutitang fm.);d-黏土矿物含量与牛蹄塘组样品总孔比表面积相关性(correlation between clay mineral content and total pore specific surface area of samples from Niutitang fm.);1-微孔(micropore);2-中孔(mesopore);3-大孔(macropore)
4 结论

(1) 渝东南五峰-龙马溪组与湘西北牛蹄塘组的孔隙发育差异主要集中在中孔与大孔,孔隙的发育程度影响了牛蹄塘组页岩的气流通道. 基于实验测试结果与数据分析发现,五峰-龙马溪组与牛蹄塘组均能为页岩气提供足够的吸附表面.

(2) 焦页1井与慈页1井钻、测井资料揭示,牛蹄塘组较五峰-龙马溪组经历了更深的历史埋深,强烈的压实作用收缩了牛蹄塘组中的部分孔隙,造成了牛蹄塘组与五峰-龙马溪组页岩气赋存空间的差异.

(3) 五峰-龙马溪组页岩与牛蹄塘组页岩中TOC均与微孔发育有良好的正相关关系,表明有机质孔对储层整体孔隙发育提供了一定贡献,证明了五峰-龙马溪组页岩中略高于牛蹄塘组页岩的TOC相对发育了更多的孔隙空间.

(4) 根据刚性矿物与孔隙发育的相关系数,发现石英、黄铁矿等硬度较大、抗机械压实能力强的刚性矿物可以有效地保留原生孔隙、粒间孔的孔隙形态,保存微孔. 石英因生物成因贡献的含量不同而对中孔、大孔的保护程度不一,黄铁矿则可以根据含量的多寡为大孔提供一定程度的保护,而长石、碳酸盐矿物等硬度稍弱、含量较低的矿物与孔隙发育的相关性较混乱,表明不同刚性矿物对孔隙发育的贡献不一. 根据化学性质的稳定性强弱与矿物含量,五峰-龙马溪组中较高含量的刚性矿物形成了强于牛蹄塘组的刚性矿物格架,为储层孔隙发育提供了更有利的贡献.

(5) 黏土矿物多发育狭缝状矿物孔隙,根据其塑性易压实的特征,在牛蹄塘组更强的压实作用下很难保留孔隙空间,为储层孔隙发育提供有利贡献.

参考文献
[1]
邹才能, 董大忠, 王玉满, 等. 中国页岩气特征、挑战及前景(一)[J]. 石油勘探与开发, 2015, 42(6): 689-701.
Zou C N, Dong D Z, Wang Y M, et al. Shale gas in China: characteristics, challenges and prospects (Ⅰ)[J]. Petroleum Exploration and Development, 2015, 42(6): 689-701. DOI:10.11698/PED.2015.06.01
[2]
邹才能, 董大忠, 王玉满, 等. 中国页岩气特征、挑战及前景(二)[J]. 石油勘探与开发, 2016, 43(2): 166-178.
Zou C N, Dong D Z, Wang Y M, et al. Shale gas in China: characteristics, challenges and prospects (Ⅱ)[J]. Petroleum Exploration and Development, 2016, 43(2): 166-178. DOI:10.11698/PED.2016.02.02
[3]
Chalmers G R, Bustin R M, Power I M. Characterization of gas shale pore systems by porosimetry, pycnometry, surface area, and field emission scanning electron microscopy/transmission electron microscopy image analyses: examples from the Barnett, Woodford, Haynesville, Marcellus, and Doig units[J]. AAPG Bulletin, 2012, 96(6): 1099-1119. DOI:10.1306/10171111052
[4]
Hao F, Zou H Y, Lu Y C. Mechanisms of shale gas storage: Implications for shale gas exploration in China[J]. AAPG Bulletin, 2013, 97(8): 1325-1346. DOI:10.1306/02141312091
[5]
田涛, 付德亮, 杨甫, 等. 米仓山-汉南隆起区牛蹄塘组页岩矿物组分与微观孔隙的关系[J]. 煤炭学报, 2018, 43(S1): 236-244.
Tian T, Fu D L, Yang F, et al. Relationship between mineral composition and micro-pores of Niutitang-Formation shale in Micangshan-Hannan Uplift[J]. Journal of China Coal Society, 2018, 43(S1): 236-244.
[6]
周永刚. 中上扬子地块浅部褶皱逆冲格局: 遥感卫星图像处理与解释[D]. 青岛: 中国海洋大学, 2009.
Zhou Y G. The surface-outcropped structural pattern of folds and thrusts in the Upper-Middle Yangtze block: Processing and interpretation of remote sensing satellite images[J]. Qingdao: Ocean University of China, 2009.
[7]
郭旭升. 南方海相页岩气"二元富集"规律——四川盆地及周缘龙马溪组页岩气勘探实践认识[J]. 地质学报, 2014, 88(7): 1209-1218.
Guo X S. Rules of two-factor enrichment for marine shale gas in southern China-understanding from the Longmaxi Formation shale gas in Sichuan Basin and its surrounding area[J]. Acta Geologica Sinica, 2014, 88(7): 1209-1218.
[8]
Hu H Y, Hao F, Lin J F, et al. Organic matter-hosted pore system in the Wufeng-Longmaxi (O3w-S1l) shale, Jiaoshiba area, Eastern Sichuan Basin, China[J]. International Journal of Coal Geology, 2017, 173: 40-50. DOI:10.1016/j.coal.2017.02.004
[9]
金之钧, 郑和荣, 蔡立国, 等. 中国前中生代海相烃源岩发育的构造-沉积条件[J]. 沉积学报, 2010, 28(5): 875-883.
Jin Z J, Zheng R H, Cai L G, et al. Tectonic-sedimentary conditions for development of pre-Mesozoic marine source rocks in China[J]. Acta Sedimentologica Sinica, 2010, 28(5): 875-883.
[10]
扈金刚. 湘西北地区富有机质页岩孔隙结构及其演化特征研究[D]. 武汉: 中国地质大学, 2016.
Hu J G. Study on pore structure and evolution characteristics of organic-rich shale in northwestern Hunan province[J]. Wuhan: China University of Geosciences, 2016. (in Chinese)
[11]
郭旭升, 胡东风, 魏志红, 等. 涪陵页岩气田的发现与勘探认识[J]. 中国石油勘探, 2016, 21(3): 24-37.
Guo X S, Hu D F, Wei Z H, et al. Discovery and exploration of Fuling shale gas field[J]. China Petroleum Exploration, 2016, 21(3): 24-37.
[12]
Hao F, Zou H Y. Cause of shale gas geochemical anomalies and mechanisms for gas enrichment and depletion in high-maturity shales[J]. Marine and Petroleum Geology, 2013, 44: 1-12. DOI:10.1016/j.marpetgeo.2013.03.005
[13]
郭彤楼. 涪陵页岩气田发现的启示与思考[J]. 地学前缘, 2016, 23(1): 29-43.
Guo T L. Discovery and characteristics of the Fuling shale gas field and its enlightenment and thinking[J]. Earth Science Frontiers, 2016, 23(1): 29-43.
[14]
戴方尧. 川东-湘西地区龙马溪组与牛蹄塘组页岩孔隙与页岩气赋存机理研究[D]. 武汉: 中国地质大学, 2018.
Dai F Y. The study of pores characteristics and shale gas occurrence of Longmaxi and Niutitang Formation in East of Sichuan and West of Hunan area[J]. Wuhan: China University of Geosciences, 2018.
[15]
Rouquerol J, Avnir D, Fairbridge C W, et al. Recommendations for the characterization of porous solids (technical report)[J]. Pure and Applied Chemistry, 1994, 66(8): 1739-1758. DOI:10.1351/pac199466081739
[16]
罗超, 刘树根, 罗立志, 等. 贵州丹寨南皋下寒武统牛蹄塘组黑色页岩孔隙结构特征[J]. 地质科技情报, 2014, 33(3): 93-105.
Luo C, Liu S G, Luo L Z, et al. Pore structure characteristics of black shale in the lower Cambrian Niutitang Formation of Nangao section in Danzhai, Guizhou province[J]. Geological Science and Technology Information, 2014, 33(3): 93-105.
[17]
陈相霖, 郭天旭, 石砥石, 等. 陕南地区牛蹄塘组页岩孔隙结构特征及吸附能力[J]. 岩性油气藏, 2019, 31(5): 52-60.
Chen X L, Guo T X, Shi D S, et al. Pore structure characteristics and adsorption capacity of Niutitang Formation shale in southern Shaanxi[J]. Lithologic Reservoirs, 2019, 31(5): 52-60.
[18]
冯小龙, 敖卫华, 唐玄. 陆相页岩气储层孔隙发育特征及其主控因素分析: 以鄂尔多斯盆地长7段为例[J]. 吉林大学学报(地球科学版), 2018, 48(3): 678-692.
Feng X L, Ao W H, Tang X. Characteristics of pore development and its main controlling factors of continental shale gas reservoirs: a case study of Chang 7 member in Ordos Basin[J]. Journal of Jilin University (Earth Science Edition), 2018, 48(3): 678-692.
[19]
Curtis J B. Fractured shale-gas systems[J]. AAPG Bulletin, 2002, 86(11): 1921-1938.
[20]
Kinley T J, Cook L W, Breyer J A, et al. Hydrocarbon potential of the Barnett shale (Mississippian), Delaware Basin, West Texas and southeastern New Mexico[J]. AAPG Bulletin, 2008, 92(8): 967-991.
[21]
Loucks R G, Reed R M, Ruppel S C, et al. Morphology, genesis, and distribution of nanometer-scale pores in siliceous mudstones of the Mississippian Barnett shale[J]. Journal of Sedimentary Research, 2009, 79(12): 848-861.
[22]
Jarvie D M, Hill R J, Ruble T E, et al. Unconventional shale-gas systems: the Mississippian Barnett shale of north-central Texas as one model for thermogenic shale-gas assessment[J]. AAPG Bulletin, 2007, 91(4): 475-499.
[23]
Hickey J J, Henk B. Lithofacies summary of the Mississippian Barnett shale, Mitchell 2 T.P. Sims well, Wise county, Texas[J]. AAPG Bulletin, 2007, 91(4): 437-443.
[24]
Thyberg B, Jahren J, Winje T, et al. From mud to shale: rock stiffening by micro-quartz cementation[J]. First Break, 2009, 27(2): 170-173.
[25]
Loucks R G, Reed R M, Ruppel S C, et al. Spectrum of pore types and networks in mudrocks and a descriptive classification for matrix-related mudrock pores[J]. AAPG Bulletin, 2012, 96(6): 1071-1098.