Characteristics of organic matter-hosted pores in Lower Silurian Longmaxi shale with different maturities, Sichuan Basin
-
摘要: 有机质孔隙是页岩气的主要储集空间,也是页岩天然渗流通道的重要组成部分。选取四川盆地不同热成熟度的下志留统龙马溪组页岩,采用场发射扫描电镜开展页岩不同显微组分有机质孔隙形成演化研究。笔石是龙马溪组页岩主要的结构有机质,含量较少,自身不发育有机质孔隙。成岩过程中由脂类原位聚合或外部地质聚合物交代使得笔石化石具有一定的生烃潜力,导致局部存在有机质孔隙。固体沥青是龙马溪组页岩最主要的显微组分,也是有机质孔隙发育的主要载体。考虑细粒沉积物成岩和有机质生烃演化,结合固体沥青赋存形态,可将固体沥青区分为前油沥青和后油沥青,且后油沥青含量占绝对优势。固体沥青有机质孔隙演化与热成熟度密切相关。总体上,随着热成熟度增加,固体沥青有机质孔隙越来越发育。成熟-高成熟早期(GRo < 2.3%),固体沥青孔隙不太发育,可能受到有机质生成的烃类物质掩盖。高成熟晚期-过成熟早期(2.3% < GRo < 4.5%)是固体沥青有机质孔隙大量发育的主要时期,含海绵状孔隙和气泡状孔隙2种类型,富有机质页岩有机质孔隙度对总孔隙度的贡献达50%以上。过成熟晚期(GRo > 4.5%),有机质炭化对页岩孔隙产生强烈破坏作用,导致页岩气勘探风险加剧。Abstract: Organic matter-hosted pores provide reservoir space and migration pathways for shale gas. The evolution of organic matter-hosted pores (OM pores) of different macerals from Longmaxi shale with a wide variety of thermal maturities has been investigated using field emission scanning electron microscopy (FE-SEM). The Longmaxi shale contains rare graptolites which are the main component of structured organic matter. No OM pores occur in graptolite fragments, irrespective of thermal maturity. OM pores locally developed in graptolite fragments are formed from hydrocarbon generation of organic matter which was replaced by macromolecular material from surrounding sediment or in situ polymerized by lipids from the organism itself. Solid bitumen is not only the major organic component in the Longmaxi shale, but also the main host of OM pore development. The diagenesis of fine-grained sediments and thermal evolution of organic matter have been combined with the morphology of solid bitumen to distinguish pre-oil solid bitumen and post-oil solid bitumen. The post-oil solid bitumen is dominant. The evolution of OM pores within solid bitumen is closely related to thermal maturity. Generally, OM pores within solid bitumen become greater as thermal maturity increases. During the mature to early postmature (GRo < 2.3%) stages, OM pores within solid bitumen are not well developed probably due to the masking by oil and bitumen generated from organic matter. OM pores within solid bitumen are well developed during the late postmature to early overmature (2.3% < GRo < 4.5%) stages, with two main types being spongy and bubble-shaped. For organic-rich Longmaxi shale, the contribution of OM porosity to total porosity is more than 50%. During the late overmature (GRo>4.5%) stage, organic matter carbonization will cause intense damage to shale pores so that the exploration risk of shale gas increases.
-
Key words:
- organic matter-hosted pore /
- thermal maturity /
- maceral /
- solid bitumen /
- shale /
- Longmaxi Formation /
- Lower Silurian /
- Sichuan Basin
-
表 1 四川盆地龙马溪组页岩样品基本参数
Table 1. Basic parameters of Longmaxi shale, Sichuan Basin
样品编号 深度/m 有机碳含量/% 矿物组成/% 黏土 石英 长石 方解石 白云石 黄铁矿 其他 CMB 露头 2.12 36.6 53.0 4.4 0.9 0.6 3.2 1.3 YC1 1 099.0 1.11 55.4 31.2 5.7 1.4 0.8 1.0 4.5 CHP 露头 4.05 26.8 63.8 3.9 1.1 0.2 2.8 1.4 DBY 露头 4.87 39.1 53.3 1.3 0.9 0.1 1.6 3.7 GD1 1 247.1 1.17 38.7 40.4 11.5 4.5 1.2 2.1 1.6 WY35 3 711.9 3.43 45.3 29.7 8.0 3.5 5.8 6.2 1.5 N208 1 269.3 1.21 45.0 34.1 10.1 5.7 2.0 1.9 1.2 YY1 3 813.6 5.04 38.5 45.6 3.9 2.3 3.2 5.2 1.3 PY1 2 153.3 2.47 48.4 42.4 4.9 0.3 0.8 1.7 1.5 LY1 2 829.3 4.58 25.2 59.6 6.7 2.7 1.7 2.3 1.8 JY41 2 609.3 3.74 48.6 38.0 6.4 1.0 1.8 2.6 1.6 YZ1 4 503.1 4.81 35.9 50.9 7.0 0.3 1.5 1.4 3.0 MY1 3 093.2 3.66 4.8 9.2 0.7 34.6 49.0 1.3 0.4 表 2 四川盆地涪陵页岩气田焦页2井龙马溪组页岩有机显微组分组成特征
Table 2. Maceral groups of Longmaxi shale from well Jiaoye 2, Fuling Shale Gas Field, Sichuan Basin
深度/m 层位 有机碳含量/% 全岩有机显微组分含量/% 固体沥青 动物碎屑 类脂组 合计 2 542.68 下志留统 2.95 5 0.2 0.1 5.3 2 567.62 下志留统 3.82 7 0.2 0.1 7.3 2 568.50 下志留统 7.13 15 0.4 0.1 15.5 2 572.30 上奥陶统 5.27 10 0.2 0.1 10.3 表 3 四川盆地龙马溪组页岩固体沥青扫描电镜有机质孔隙度与计算有机质孔隙度数据
Table 3. Calculated organic matter porosity based on SEM of solid bitumen in Longmaxi shale in Sichuan Basin
样品编号 w(TOC)/% SEM有机质孔隙度/% 含孔有机质含量/% 有机质孔隙度1/% 有机质孔隙度2/% YC1 1.11 0.38 2.81 0.01 0.02 CHP 4.05 1.20 9.92 0.12 0.18 DBY 4.87 28.89 11.82 3.42 5.25 GD1 1.17 29.35 2.96 0.87 1.34 WY35 3.43 27.95 8.46 2.37 3.64 N208 1.21 21.20 3.06 0.65 0.99 YY1 5.04 16.23 12.21 1.98 3.05 PY1 2.47 17.72 6.16 1.09 1.68 LY1 4.58 20.04 11.16 2.24 3.44 JY41 3.74 31.34 9.19 2.88 4.43 YZ1 4.81 27.49 11.69 3.21 4.94 MY1 3.66 15.40 9.01 1.39 2.13 注:含孔有机质含量=w(TOC)×0.95/[w(TOC)/1.25+(100-w(TOC))/2.7];有机质孔隙度1=SEM有机质孔隙度×含孔有机质含量/100,有机质孔隙度2=有机质孔隙度1/0.65。 -
[1] 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. doi: 10.2110/jsr.2009.092 [2] MILLIKEN K L, RUDNICKI M, AWWILLER D N, et al. Organic matter-hosted pore system, Marcellus Formation (Devonian), Pennsylvania[J]. AAPG Bulletin, 2013, 97(2): 177-200. doi: 10.1306/07231212048 [3] MILLIKEN K L, ESCH W L, REED R M, et al. Grain assemblages and strong diagenetic overprinting in siliceous mudrocks, Barnett shale (Mississippian), Fort Worth Basin, Texas[J]. AAPG Bulletin, 2012, 96(8): 1553-1578. doi: 10.1306/12011111129 [4] LÖHR S C, BARUCH E T, HALL P A, et al. Is organic pore deve-lopment in gas shales influenced by the primary porosity and structure of thermally immature organic matter?[J]. Organic Geochemistry, 2015, 87: 119-132. doi: 10.1016/j.orggeochem.2015.07.010 [5] 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. doi: 10.1306/12190606068 [6] 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. doi: 10.1306/08171111061 [7] CURTIS M E, CARDOTT B J, SONDERGELD C H, et al. Development of organic porosity in the Woodford shale with increasing thermal maturity[J]. International Journal of Coal Geology, 2012, 103: 26-31. doi: 10.1016/j.coal.2012.08.004 [8] BERNARD S, HORSFIELD B, SCHULZ H M, et al. Geochemical evolution of organic-rich shales with increasing maturity: a STXM and TEM study of the Posidonia shale (Lower Toarcian, northern Germany)[J]. Marine and Petroleum Geology, 2012, 31(1): 70-89. doi: 10.1016/j.marpetgeo.2011.05.010 [9] CHEN Ji, XIAO Xianming. Evolution of nanoporosity in organic-rich shales during thermal maturation[J]. Fuel, 2014, 129: 173-181. doi: 10.1016/j.fuel.2014.03.058 [10] CARDOTT B J, LANDIS C R, CURTIS M E. Post-oil solid bitumen network in the Woodford shale, USA: a potential primary migration pathway[J]. International Journal of Coal Geology, 2015, 139: 106-113. doi: 10.1016/j.coal.2014.08.012 [11] 王飞宇, 关晶, 冯伟平, 等. 过成熟海相页岩孔隙度演化特征和游离气量[J]. 石油勘探与开发, 2013, 40(6): 764-768. https://www.cnki.com.cn/Article/CJFDTOTAL-SKYK201306020.htmWANG Feiyu, GUAN Jing, FENG Weiping, et al. Evolution of over mature marine shale porosity and implication to the free gas volume[J]. Petroleum Exploration and Development, 2013, 40(6): 764-768. https://www.cnki.com.cn/Article/CJFDTOTAL-SKYK201306020.htm [12] TIAN Hui, PAN Lei, XIAO Xianming, et al. A preliminary study on the pore characterization of Lower Silurian black shales in the Chuandong Thrust Fold Belt, southwestern China using low pressure N2 adsorption and FE-SEM methods[J]. Marine and Petroleum Geology, 2013, 48: 8-19. doi: 10.1016/j.marpetgeo.2013.07.008 [13] HU Haiyan, HAO Fang, LIN Junfeng, 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 [14] JULIAO T, SUÁREZ-RUIZ I, MARQUEZ R, et al. The role of solid bitumen in the development of porosity in shale oil reservoir rocks of the Upper Cretaceous in Colombia[J]. International Journal of Coal Geology, 2015, 147-148: 126-144. doi: 10.1016/j.coal.2015.07.001 [15] SCHIEBER J. SEM observations on ion-milled samples of Devonian black shales from Indiana and New York: the petrographic context of multiple pore types[M]//CAMP W K, DIAZ E, WAWAK B. Electron microscopy of shale hydrocarbon reservoirs. [s. l. ]: AAPG, 2013: 153-171. [16] LIU Bei, SCHIEBER J, MASTALERZ M. Combined SEM and reflected light petrography of organic matter in the New Albany shale (Devonian-Mississippian) in the Illinois Basin: a perspective on organic pore development with thermal maturation[J]. International Journal of Coal Geology, 2017, 184: 57-72. doi: 10.1016/j.coal.2017.11.002 [17] LI Yifan, SCHIEBER J, FAN Tailiang, et al. Pore characterization and shale facies analysis of the Ordovician-Silurian transition of northern Guizhou, South China: the controls of shale facies on pore distribution[J]. Marine and Petroleum Geology, 2018, 92: 697-718. doi: 10.1016/j.marpetgeo.2017.12.001 [18] REED R M, LOUCKS R G, RUPPEL S C. Comment on "Formation of nanoporous pyrobitumen residues during maturation of the Barnett shale (Fort Worth Basin)" by BERNARD et al. (2012)[J]. International Journal of Coal Geology, 2014, 127: 111-113. doi: 10.1016/j.coal.2013.11.012 [19] FISHMAN N S, HACKLEY P C, LOWERS H A, et al. The nature of porosity in organic-rich mudstones of the Upper Jurassic Kimmeridge Clay Formation, North Sea, offshore United Kingdom[J]. International Journal of Coal Geology, 2012, 103: 32-50. doi: 10.1016/j.coal.2012.07.012 [20] WEI Lin, MASTALERZ M, SCHIMMELMANN A, et al. Influence of Soxhlet-extractable bitumen and oil on porosity in thermally maturing organic-rich shales[J]. International Journal of Coal Geology, 2014, 132: 38-50. doi: 10.1016/j.coal.2014.08.003 [21] QI Yu, JU Yiwen, CAI Jianchao, et al. The effects of solvent extraction on nanoporosity of marine-continental coal and mudstone[J]. Fuel, 2019, 235: 72-84. doi: 10.1016/j.fuel.2018.07.083 [22] CANDER H. Sweet spots in shale gas and liquids plays: prediction of fluid composition and reservoir pressure[C]//AAPG Annual Convention and Exhibition, April 22-25, 2012. Long Beach, CA, USA, 2012. [23] XIAO Xianming, WEI Qiang, Gai Haifeng, et al. Main controlling factors and enrichment area evaluation of shale gas of the Lower Paleozoic marine strata in South China[J]. Petroleum Science, 2015, 12(4): 573-586. doi: 10.1007/s12182-015-0057-2 [24] 牟传龙, 王秀平, 王启宇, 等. 川南及邻区下志留统龙马溪组下段沉积相与页岩气地质条件的关系[J]. 古地理学报, 2016, 18(3): 457-472. https://www.cnki.com.cn/Article/CJFDTOTAL-GDLX201603012.htmMOU Chuanlong, WANG Xiuping, WANG Qiyu, et al. Relationship between sedimentary facies and shale gas geological conditions of the Lower Silurian Longmaxi Formation in southern Sichuan Basin and its adjacent areas[J]. Journal of Palaeogeo-graphy, 2016, 18(3): 457-472. https://www.cnki.com.cn/Article/CJFDTOTAL-GDLX201603012.htm [25] BERTRAND R, HÉROUX Y. Chitinozoan, graptolite, and scoleco-dont reflectance as an alternative to vitrinite and pyrobitumen reflectance in Ordovician and Silurian strata, Anticosti Island, Quebec, Canada[J]. AAPG Bulletin, 1987, 71(8): 951-957. [26] CURIALE J A. Origin of solid bitumens, with emphasis on biological marker results[J]. Organic Geochemistry, 1986, 10(1/3): 559-580. [27] GAO Jian, HE Sheng, ZHAO Jianxin, et al. Geothermometry and geobarometry of overpressured Lower Paleozoic gas shales in the Jiaoshiba field, Central China: insight from fluid inclusions in fracture cements[J]. Marine and Petroleum Geology, 2017, 83: 124-139. doi: 10.1016/j.marpetgeo.2017.02.018 [28] XIONG Yongqiang, JIANG Wenmin, WANG Xiaotao, et al. Formation and evolution of solid bitumen during oil cracking[J]. Marine and Petroleum Geology, 2016, 78: 70-75. doi: 10.1016/j.marpetgeo.2016.09.008 [29] MASTALERZ M, DROBNIAK A, STANKIEWICZ A B. Origin, properties, and implications of solid bitumen in source-rock reservoirs: a review[J]. International Journal of Coal Geology, 2018, 195: 14-36. doi: 10.1016/j.coal.2018.05.013 [30] ZHAO Jianhua, JIN Zhijun, JIN Zhenkui, et al. Mineral types and organic matters of the Ordovician-Silurian Wufeng and Longmaxi shale in the Sichuan Basin, China: implications for pore systems, diagenetic pathways, and reservoir quality in fine-grained sedimentary rocks[J]. Marine and Petroleum Geology, 2017, 86: 655-674. doi: 10.1016/j.marpetgeo.2017.06.031 [31] BEHAR F, VANDENBROUCKE M, TANG Yongchun, et al. Thermal cracking of kerogen in open and closed systems: determination of kinetic parameters and stoichiometric coefficients for oil and gas generation[J]. Organic Geochemistry, 1997, 26(5/6): 321-339. [32] 仰云峰. 川东南志留系龙马溪组页岩沥青反射率和笔石反射率的应用[J]. 石油实验地质, 2016, 38(4): 466-472. doi: 10.11781/sysydz201604466YANG Yunfeng. Application of bitumen and graptolite reflectance in the Silurian Longmaxi shale, southeastern Sichuan Basin[J]. Petroleum Geology & Experiment, 2016, 38(4): 466-472. doi: 10.11781/sysydz201604466 [33] GOODARZI F, FOWLER M G, BUSTIN M, et al. Thermal maturity of Early Paleozoic sediments as determined by the optical properties of marine-derived organic matter: a review[C]//SCHIDLOWSKI M, GOLUBIC S, KIMBERLEY M M, et al. Early organic evolution. Berlin, Heidelberg: Springer, 1992: 279-295. [34] 戴娜, 钟宁宁, 张瑜, 等. 氩离子抛光/扫描电镜分析方法在笔石有机质研究中的应用[J]. 电子显微学报, 2015, 34(5): 416-420. https://www.cnki.com.cn/Article/CJFDTOTAL-DZXV201505011.htmDAI Na, ZHONG Ningning, ZHANG Yu, et al. Ar ion milling/SEM analysis on graptolitinite macerals[J]. Journal of Chinese Electron Microscopy Society, 2015, 34(5): 416-420. https://www.cnki.com.cn/Article/CJFDTOTAL-DZXV201505011.htm [35] BRIGGS D E G, KEAR A J, BAAS M, et al. Decay and composition of the hemichordate Rhabdopleura: implications for the taphonomy of graptolites[J]. Lethaia, 1995, 28(1): 15-23. doi: 10.1111/j.1502-3931.1995.tb01589.x [36] CROWTHER P R. The fine structure of graptolite periderm[M]. London: The Palaeontological Association, 1981. [37] GUPTA N S, BRIGGS D E G, PANCOST R D. Molecular taphonomy of graptolites[J]. Journal of the Geological Society, 2006, 163(6): 897-900. doi: 10.1144/0016-76492006-070 [38] 申宝剑, 仰云峰, 腾格尔, 等. 四川盆地焦石坝构造区页岩有机质特征及其成烃能力探讨: 以焦页1井五峰-龙马溪组为例[J]. 石油实验地质, 2016, 38(4): 480-488. doi: 10.11781/sysydz201604480SHEN Baojian, YANG Yunfeng, TENGER, et al. Characteristics and hydrocarbon significance of organic matter in shale from the Jiaoshiba structure, Sichuan Basin: a case study of the Wufeng-Longmaxi formations in well Jiaoye1[J]. Petroleum Geology & Experiment, 2016, 38(4): 480-488. doi: 10.11781/sysydz201604480 [39] 卢龙飞, 秦建中, 申宝剑, 等. 中上扬子地区五峰组-龙马溪组硅质页岩的生物成因证据及其与页岩气富集的关系[J]. 地学前缘, 2018, 25(4): 226-236. https://www.cnki.com.cn/Article/CJFDTOTAL-DXQY201804022.htmLU Longfei, QIN Jianzhong, SHEN Baojian, et al. The origin of biogenic silica in siliceous shale from Wufeng-Longmaxi formation in the Middle and Upper Yangtze region and its relationship with shale gas enrichment[J]. Earth Science Frontiers, 2018, 25(4): 226-236. https://www.cnki.com.cn/Article/CJFDTOTAL-DXQY201804022.htm [40] SCHIEBER J, KRINSLEY D, RICIPUTI L. Diagenetic origin of quartz silt in mudstones and implications for silica cycling[J]. Nature, 2000, 406(6799): 981-985. doi: 10.1038/35023143 [41] DAY-STIRRAT R J, DUTTON S P, MILLIKEN K L, et al. Fabric anisotropy induced by primary depositional variations in the silt: clay ratio in two fine-grained slope fan complexes: Texas Gulf Coast and northern North Sea[J]. Sedimentary Geology, 2010, 226(1/4): 42-53. [42] SEEWALD J S. Organic-inorganic interactions in petroleum-producing sedimentary basins[J]. Nature, 2003, 426(6964): 327-333. doi: 10.1038/nature02132 [43] KO L T, RUPPEL S C, LOUCKS R G, et al. Pore-types and pore-network evolution in Upper Devonian-Lower Mississippian Woodford and Mississippian Barnett mudstones: insights from laboratory thermal maturation and organic petrology[J]. International Journal of Coal Geology, 2018, 190: 3-28. doi: 10.1016/j.coal.2017.10.001 [44] JI Wenming, SONG Yan, JIANG Zhenxue, et al. Micron-to nano-pore characteristics in the shale of Longmaxi Formation, southeast Sichuan Basin[J]. Petroleum Research, 2017, 2(2): 156-168. doi: 10.1016/j.ptlrs.2017.07.003 [45] 郭彤楼, 张汉荣. 四川盆地焦石坝页岩气田形成与富集高产模式[J]. 石油勘探与开发, 2014, 41(1): 28-36. https://www.cnki.com.cn/Article/CJFDTOTAL-SKYK201401003.htmGUO Tonglou, ZHANG Hanrong. Formation and enrichment mode of Jiaoshiba Shale Gas Field, Sichuan Basin[J]. Petroleum Exploration and Development, 2014, 41(1): 28-36. https://www.cnki.com.cn/Article/CJFDTOTAL-SKYK201401003.htm [46] 李金磊, 尹成, 王明飞, 等. 四川盆地涪陵焦石坝地区保存条件差异性分析[J]. 石油实验地质, 2019, 41(3): 341-347. doi: 10.11781/sysydz201903341LI Jinlei, YIN Cheng, WANG Mingfei, et al. Preservation condition differences in Jiaoshiba area, Fuling, Sichuan Basin[J]. Petroleum Geology & Experiment, 2019, 41(3): 341-347. doi: 10.11781/sysydz201903341 [47] 易积正, 王超. 四川盆地焦石坝地区龙马溪组海相页岩储层非均质性特征[J]. 石油实验地质, 2018, 40(1): 13-19. doi: 10.11781/sysydz201801013YI Jizheng, WANG Chao. Differential pore development characteristics in various shale lithofacies of Longmaxi Formation in Jiaoshiba area, Sichuan Basin[J]. Petroleum Geology & Experiment, 2018, 40(1): 13-19. doi: 10.11781/sysydz201801013 [48] 刘鹏, 吴佩津, 彭钰洁. 焦石坝地区构造特征及页岩气保存模式研究[J]. 特种油气藏, 2018, 25(2): 37-41. doi: 10.3969/j.issn.1006-6535.2018.02.007LIU Peng, WU Peijin, PENG Yujie. Structure characterization and shale gas preservation pattern in Jiaoshiba[J]. Special Oil & Gas Reservoirs, 2018, 25(2): 37-41. doi: 10.3969/j.issn.1006-6535.2018.02.007 [49] 王玉满, 李新景, 陈波, 等. 海相页岩有机质炭化的热成熟度下限及勘探风险[J]. 石油勘探与开发, 2018, 45(3): 385-395. https://www.cnki.com.cn/Article/CJFDTOTAL-SKYK201803004.htmWANG Yuman, LI Xinjing, CHEN Bo, et al. Lower limit of thermal maturity for the carbonization of organic matter in marine shale and its exploration risk[J]. Petroleum Exploration and Development, 2018, 45(3): 385-395. https://www.cnki.com.cn/Article/CJFDTOTAL-SKYK201803004.htm -