Characteristics and genesis of fillings in fracture-cavity space in first member of Permian Maokou Formation, Sichuan Basin: a case study of well A1
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摘要: 近年来,四川盆地二叠系茅口组一段不断取得天然气发现,其泥灰岩的储集空间成因机制已成为关注的问题之一。厘米级缝洞型储集空间是茅口组一段新发现的储集空间类型之一,相关研究尚未公开报道。以四川盆地A1井为例,在岩心观察描述基础上,通过显微岩石学、碳氧同位素、锶同位素与微量元素的对比分析,研究了缝洞充填物特征及成因。茅口组一段缝洞中方解石胶结物与泥灰岩基质具有相似的碳氧同位素与锶同位素分布特征,表明方解石主要来源于围岩的溶解再沉淀;与泥灰岩相比,缝洞方解石胶结物的变价元素(V、Cr、U、Mo)、稀土元素(REE)含量降低,而微营养元素(Ni、Cu、Zn)含量升高,揭示了在此过程中微量元素的差异性迁移规律;方解石与泥灰岩基质的Mn与Sr含量的差异性变化特征揭示了成岩流体的海水亲缘属性,进一步表明其与大气淡水、深部热液流体无关。晚侏罗世以来的侧向构造推覆挤压力,形成了川东南地区滑脱断层及相关褶皱体系,在此过程中可能导致了茅口组泥灰岩变形并产生了厘米级裂缝空间。泥灰岩在后续压实—压溶作用(包括侧向压溶)等形成的成岩流体为缝洞石英和方解石胶结物提供了物质来源。Abstract: In recent years, natural gas discoveries have been continuously made in the first member of the Permian Maokou Formation in the Sichuan Basin, bringing attention to the genesis mechanism of marlstone reservoir space. Centimeter-scale fracture-cavity type reservoir space is one of the newly discovered types in the first member of the Maokou Formation, and relevant research has not been publicly reported. Taking well A1 in the Sichuan Basin as an example, based on core observation and description, the characteristics and genesis of fracture-cavity fillings were studied through comparative analysis of microscopic petrology, carbon-oxygen isotopes, strontium isotopes, and trace elements. The similar distribution characteristics of carbon-oxygen isotopes and strontium isotopes between calcite cement and mudstone matrix in the fractures of the first member of the Maokou Formation indicated that calcite mainly came from the dissolution and redeposition of surrounding rocks. Compared with marlstone, the fracture calcite cement showed lower contents of valence elements (V, Cr, U, Mo) and rare earth elements (REE), while the content of micronutrient elements (Ni, Cu, Zn) increased, revealing the differential migration pattern of trace elements in this process. The differential variation characteristics of Mn and Sr contents between calcite and marl matrix revealed the marine affinity of diagenetic fluids, further indicating their independence from atmospheric freshwater and deep hydrothermal fluids. Since the Late Jurassic, lateral tectonic thrusting pressure has formed detachment faults and related fold systems in southeastern Sichuan, which potentially caused deformation of the Maokou Formation marlstone and the generation of centimeter-scale fracture spaces. Diagenetic fluids formed during subsequent compaction-dissolution processes (including lateral dissolution) provided material sources for quartz and calcite cement in the fractures.
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Key words:
- diagenesis /
- clay mineral /
- marlstone /
- Maokou Formation /
- Permian /
- Sichuan Basin
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图 2 四川盆地A1井茅口组一段缝洞充填物特征
a.近似顺层的非连续薄弱面(黄色箭头)被方解石充填,泥质灰岩,2 860.24 m;b.顺层侧向挤压形成的变形特征且被方解石胶结物全充填(黄色虚线区域),泥质灰岩,2 860.24 m;c.垂直层面压溶缝合线与缝洞石英—方解石半充填,泥灰岩,2 839.00 m;d-e.缝洞空间发育粒状石英与巨晶方解石胶结物,泥灰岩基质部分富含有机质(暗色部分),2 835.85 m。
Figure 2. Characteristics of fillings in fracture-cavity space in first member of Maokou Formation in well A1, Sichuan Basin
表 1 四川盆地A1井茅口组一段泥灰岩基质与缝洞方解石碳氧同位素与锶同位素分析结果
Table 1. Results of carbon, oxygen, and strontium isotope analysis of marlstone matrix and fracture-cavity calcite cement in first member of Maokou Formation in well A1, Sichuan Basin
序号 样品号 深度/m 分析对象 δ13CV-PDB/‰ δ18OV-PDB/‰ 87Sr/86Sr 1倍标准误差(1σ) 1 A1-40-M 2 839.00 泥灰岩 4.24 -6.06 0.707 043 0.000 005 2 A1-40-C 2 839.00 缝洞方解石 3.03 -6.54 0.707 066 0.000 004 3 A1V-M 2 835.85 泥灰岩 2.70 -6.94 0.707 050 0.000 005 4 A1V-Cal1 2 835.85 缝洞方解石 2.83 -6.35 0.707 150 0.000 004 5 A1-45-M 2 834.20 泥灰岩 3.16 -6.93 0.707 056 0.000 004 6 A1-45-C 2 834.20 缝洞方解石 4.56 -6.15 0.707 186 0.000 004 7 A1V2-M 2 826.55 泥灰岩 3.29 -6.30 0.707 041 0.000 005 8 A1V2-Cal 2 826.55 缝洞方解石 2.28 -6.54 0.707 133 0.000 006 表 2 四川盆地A1井茅口组一段泥灰岩基质与缝洞方解石微量元素含量
Table 2. Trace element contents of marlstone matrix and fracture-cavity calcite cements in first member of Maokou Formation in well A1, Sichuan Basin
单位: μg/g 序号 样品号 分析对象 Mn Sr V Cr U Mo Ni Cu Zn La Ce Pr Nd Sm Eu Gd Tb Dy Y Ho Er Tm Yb Lu ∑REE 1 A1-40-M 泥灰岩 7.95 4 895 11.36 5.26 5.28 12.43 3.56 0.29 1.28 0.90 1.77 0.20 0.70 0.13 0.04 0.14 0.02 0.12 1.65 0.03 0.09 0.02 0.09 0.02 5.91 2 A1-40-C 缝洞方解石 6.17 5 335 0.80 1.99 0.07 0.33 4.11 0.66 2.93 0.14 0.24 0.03 0.10 0.03 0.02 0.04 0.01 0.02 0.16 0.01 0.01 0.01 0.01 0.01 0.84 3 A1V-M 泥灰岩 11.07 2 183 2.76 3.85 4.44 1.03 1.81 0.30 1.25 0.19 0.30 0.04 0.12 0.03 0.02 0.05 0.01 0.04 0.74 0.01 0.03 0.01 0.03 0.01 1.62 4 A1V-Cal 缝洞方解石 17.43 8 118 1.48 1.79 0.05 0.18 4.26 0.76 2.69 0.14 0.24 0.03 0.10 0.03 0.02 0.03 0.01 0.02 0.19 0.01 0.01 0.01 0.01 0.01 0.84 5 A1-45-M 泥灰岩 7.31 3 095 2.50 3.82 5.57 1.32 3.23 0.31 0.76 0.32 0.51 0.06 0.22 0.06 0.03 0.09 0.01 0.07 1.15 0.02 0.06 0.01 0.05 0.01 2.66 6 A1-45-C 缝洞方解石 5.13 6 221 1.30 3.46 0.04 0.19 7.34 1.85 1.41 0.11 0.19 0.02 0.08 0.02 0.02 0.04 0.01 0.02 0.36 0.01 0.01 0.00 0.01 0.00 0.91 7 A1V2-M 泥灰岩 7.73 3 286 4.59 2.41 1.46 2.14 1.31 0.42 1.19 0.33 0.59 0.07 0.27 0.06 0.03 0.08 0.01 0.06 0.77 0.02 0.04 0.01 0.03 0.01 2.37 8 A1V2-Cal 缝洞方解石 5.68 9 465 0.55 1.56 0.01 0.05 2.22 0.64 1.43 0.07 0.13 0.02 0.06 0.01 0.02 0.03 0.00 0.01 0.39 0.00 0.00 0.00 0.00 0.00 0.77 -
[1] 马永生, 蔡勋育, 赵培荣, 等. 四川盆地大中型天然气田分布特征与勘探方向[J]. 石油学报, 2010, 31(3): 347-354. https://www.cnki.com.cn/Article/CJFDTOTAL-SYXB201003000.htmMA Yongsheng, CAI Xunyu, ZHAO Peirong, et al. Distribution and further exploration of the large-medium sized gas fields in Sichuan Basin[J]. Acta Petrolei Sinica, 2010, 31(3): 347-354. https://www.cnki.com.cn/Article/CJFDTOTAL-SYXB201003000.htm [2] 张本健, 谢继容, 尹宏, 等. 四川盆地西部龙门山地区中二叠统碳酸盐岩储层特征及勘探方向[J]. 天然气工业, 2018, 38(2): 33-42. https://www.cnki.com.cn/Article/CJFDTOTAL-TRQG201802006.htmZHANG Benjian, XIE Jirong, YIN Hong, et al. Characteristics and exploration direction of the Middle Permian carbonate reservoirs in the Longmenshan Mountain areas, western Sichuan Basin[J]. Natural Gas Industry, 2018, 38(2): 33-42. https://www.cnki.com.cn/Article/CJFDTOTAL-TRQG201802006.htm [3] 胡东风, 王良军, 张汉荣, 等. 碳酸盐岩烃源岩气藏的发现及其油气地质意义: 以四川盆地涪陵地区中二叠统茅口组一段气藏为例[J]. 天然气工业, 2020, 40(7): 23-33. doi: 10.3787/j.issn.1000-0976.2020.07.003HU Dongfeng, WANG Liangjun, ZHANG Hanrong, et al. Discovery of carbonate source rock gas reservoir and its petroleum geolo-gical implications: a case study of the gas reservoir in the first member of Middle Permian Maokou Formation in the Fuling area, Sichuan Basin[J]. Natural Gas Industry, 2020, 40(7): 23-33. doi: 10.3787/j.issn.1000-0976.2020.07.003 [4] 郭彤楼. 四川盆地碳酸盐岩源岩气地质特征与勘探前景[J]. 西南石油大学学报(自然科学版), 2021, 43(1): 1-16. https://www.cnki.com.cn/Article/CJFDTOTAL-XNSY202101001.htmGUO Tonglou. Geological characteristics and exploration prospect of carbonate source rock gas in Sichuan Basin[J]. Journal of Southwest Petroleum University (Science & Technology Edition), 2021, 43(1): 1-16. https://www.cnki.com.cn/Article/CJFDTOTAL-XNSY202101001.htm [5] 苏成鹏, 李蓉, 石国山, 等. 四川盆地及周缘中二叠统茅口组一段储集层特征及对油气勘探的启示[J]. 石油勘探与开发, 2021, 48(6): 1150-1161. https://www.cnki.com.cn/Article/CJFDTOTAL-SKYK202106008.htmSU Chengpeng, LI Rong, SHI Guoshan, et al. Reservoir characteristics of the first member of Middle Permian Maokou Formation in Sichuan Basin and its periphery and inspirations to petroleum exploration, SW China[J]. Petroleum Exploration and Development, 2021, 48(6): 1150-1161. https://www.cnki.com.cn/Article/CJFDTOTAL-SKYK202106008.htm [6] 李蓉, 苏成鹏, 石国山, 等. 川南地区二叠系茅口组一段瘤状灰岩储层成因[J]. 天然气地球科学, 2021, 32(6): 806-815. https://www.cnki.com.cn/Article/CJFDTOTAL-TDKX202106003.htmLI Rong, SU Chengpeng, SHI Guoshan, et al. The genesis of nodular limestone reservoirs of the first period of Maokou Formation of Permian in southern Sichuan Basin[J]. Natural Gas Geoscience, 2021, 32(6): 806-815. https://www.cnki.com.cn/Article/CJFDTOTAL-TDKX202106003.htm [7] 张培先, 何希鹏, 高全芳, 等. 四川盆地东南缘二叠系茅口组一段页岩气藏地质特征及富集模式[J]. 石油与天然气地质, 2021, 42(1): 146-157. https://www.cnki.com.cn/Article/CJFDTOTAL-SYYT202101014.htmZHANG Peixian, HE Xipeng, GAO Quanfang, et al. Geological characteristics and enrichment pattern of Permian Mao 1 Member shale gas reservoirs at the southeastern margin of Sichuan Basin[J]. Oil & Gas Geology, 2021, 42(1): 146-157. https://www.cnki.com.cn/Article/CJFDTOTAL-SYYT202101014.htm [8] 苏成鹏, 谭秀成, 王小芳, 等. 四川盆地东部中二叠统茅口组眼球状石灰岩储层特征及成因[J]. 海相油气地质, 2020, 25(1): 55-62. doi: 10.3969/j.issn.1672-9854.2020.01.006SU Chengpeng, TAN Xiucheng, WANG Xiaofang, et al. Characteristics of eyeball-shaped limestone reservoir and its genesis of the Middle Permian Maokou Formation in east Sichuan Basin[J]. Marine Origin Petroleum Geology, 2020, 25(1): 55-62. doi: 10.3969/j.issn.1672-9854.2020.01.006 [9] MENG Qi, XUE Wuqiang, CHEN Fayao, et al. Stratigraphy of the Guadalupian (Permian) siliceous deposits from central Guizhou of South China: regional correlations with implications for carbonate productivity during the Middle Permian biocrisis[J]. Earth-Science Reviews, 2022, 228: 104011. doi: 10.1016/j.earscirev.2022.104011 [10] CHEN Fayao, XUE Wuqiang, YAN Jiaxin, et al. Alatoconchids: giant Permian bivalves from South China[J]. Earth-Science Reviews, 2018, 179: 147-167. doi: 10.1016/j.earscirev.2018.01.012 [11] 李大军, 陈辉, 陈洪德, 等. 四川盆地中二叠统茅口组储层形成与古构造演化关系[J]. 石油与天然气地质, 2016, 37(5): 756-763. https://www.cnki.com.cn/Article/CJFDTOTAL-SYYT201605016.htmLI Dajun, CHEN Hui, CHEN Hongde, et al. Relationship between reservoir development in the Middle Permian Maokou Formation and paleostructure evolution in the Sichuan Basin[J]. Oil & Gas Geology, 2016, 37(5): 756-763. https://www.cnki.com.cn/Article/CJFDTOTAL-SYYT201605016.htm [12] HAQ B U, SCHUTTER S R. A chronology of Paleozoic sea-level changes[J]. Science, 2008, 322(5898): 64-68. doi: 10.1126/science.1161648 [13] 肖笛, 谭秀成, 郗爱华, 等. 四川盆地南部中二叠统茅口组碳酸盐岩岩溶特征: 古大陆环境下层控型早成岩期岩溶实例[J]. 古地理学报, 2015, 17(4): 457-476. https://www.cnki.com.cn/Article/CJFDTOTAL-GDLX201504003.htmXIAO Di, TAN Xiucheng, XI Aihua, et al. Palaeokarst characteristics of carbonate rocks of the Middle Permian Maokou Formation in southern Sichuan Basin: example of strata-bound eogenetic karst in palaeo-continental settings[J]. Journal of Palaeogeography, 2015, 17(4): 457-476. https://www.cnki.com.cn/Article/CJFDTOTAL-GDLX201504003.htm [14] 杨明磊, 诸丹诚, 李涛, 等. 川南地区中二叠统茅口组颗粒滩对早成岩期岩溶储层的控制[J]. 现代地质, 2020, 34(2): 356-369. https://www.cnki.com.cn/Article/CJFDTOTAL-XDDZ202002016.htmYANG Minglei, ZHU Dancheng, LI Tao, et al. Control of eogenetic karst reservoir by shoals in Middle Permian Maokou Formation, southern Sichuan Basin[J]. Geoscience, 2020, 34(2): 356-369. https://www.cnki.com.cn/Article/CJFDTOTAL-XDDZ202002016.htm [15] DONG Yixin, CHEN Hongde, WANG Jiuyuan, et al. Thermal convection dolomitization induced by the Emeishan Large Igneous Province[J]. Marine and Petroleum Geology, 2020, 116: 104308. doi: 10.1016/j.marpetgeo.2020.104308 [16] FENG Ke, XU Shenglin, CHEN Anqing, et al. Middle Permian dolomites of the SW Sichuan Basin and the role of the Emeishan Large Igneous Province in their origin[J]. Marine and Petroleum Geology, 2021, 128: 104981. doi: 10.1016/j.marpetgeo.2021.104981 [17] ZHENG Haofu, MA Yongsheng, CHI Guoxiang, et al. Stratigraphic and structural control on hydrothermal dolomitization in the Middle Permian carbonates, southwestern Sichuan Basin (China)[J]. Minerals, 2019, 9(1): 32. [18] LI Shuangjian, LI Yingqiang, HE Zhiliang, et al. Differential deformation on two sides of Qiyueshan Fault along the eastern margin of Sichuan Basin, China, and its influence on shale gas preservation[J]. Marine and Petroleum Geology, 2020, 121: 104602. doi: 10.1016/j.marpetgeo.2020.104602 [19] GE Xiang, SHEN Chuanbo, SELBY D, et al. Apatite fission-track and Re-Os geochronology of the Xuefeng Uplift, China: temporal implications for dry gas associated hydrocarbon systems[J]. Geology, 2016, 44(6): 491-494. doi: 10.1130/G37666.1 [20] BUGGISCH W, WANG Xiangdong, ALEKSEEV A S, et al. Carboni-ferous- Permian carbon isotope stratigraphy of successions from China (Yangtze Platform), USA (Kansas) and Russia (Moscow Basin and Urals)[J]. Palaeogeography, Palaeoclimatology, Palaeoecology, 2011, 301(1/4): 18-38. [21] KORTE C, JONES P J, BRAND U, et al. Oxygen isotope values from high-latitudes: clues for Permian sea-surface temperature gradients and Late Palaeozoic deglaciation[J]. Palaeogeography, Palaeoclimatology, Palaeoecology, 2008, 269(1/2): 1-16. [22] STANLEY S M, HARDIE L A. Secular oscillations in the carbonate mineralogy of reef-building and sediment-producing organisms driven by tectonically forced shifts in seawater chemistry[J]. Palaeogeo-graphy, Palaeoclimatology, Palaeoecology, 1998, 144(1/2): 3-19. [23] WESTPHAL H, MUNNECKE A. Limestone-marl alternations: a warm-water phenomenon?[J]. Geology, 2003, 31(3): 263-266. doi: 10.1130/0091-7613(2003)031<0263:LMAAWW>2.0.CO;2 [24] KORTE C, KOZUR H W, BRUCKSCHEN P, et al. Strontium isotope evolution of Late Permian and Triassic seawater[J]. Geochimica et Cosmochimica Acta, 2003, 67(1): 47-62. doi: 10.1016/S0016-7037(02)01035-9 [25] VEIZER J, ALA D, AZMY K, et al. 87Sr/86Sr, δ13C and δ18O evolution of Phanerozoic seawater[J]. Chemical Geology, 1999, 161(1/3): 59-88. [26] DENISON R E, KOEPNICK R B, BURKE W H, et al. Construction of the Mississippian, Pennsylvanian and Permian seawater 87Sr/86Sr curve[J]. Chemical Geology, 1994, 112(1/2): 145-167. [27] TRIBOVILLARD N, ALGEO T J, LYONS T, et al. Trace metals as paleoredox and paleoproductivity proxies: an update[J]. Chemical Geology, 2006, 232(1/2): 12-32. [28] 胡文瑄, 陈琪, 王小林, 等. 白云岩储层形成演化过程中不同流体作用的稀土元素判别模式[J]. 石油与天然气地质, 2010, 31(6): 810-818. https://www.cnki.com.cn/Article/CJFDTOTAL-SYYT201006017.htmHU Wenxuan, CHEN Qi, WANG Xiaolin, et al. REE models for the discrimination of fluids in the formation and evolution of dolomite reservoirs[J]. Oil & Gas Geology, 2010, 31(6): 810-818. https://www.cnki.com.cn/Article/CJFDTOTAL-SYYT201006017.htm [29] 韦恒叶. 古海洋生产力与氧化还原指标: 元素地球化学综述[J]. 沉积与特提斯地质, 2012, 32(2): 76-88. https://www.cnki.com.cn/Article/CJFDTOTAL-TTSD201202013.htmWEI Hengye. Productivity and redox proxies of palaeo-oceans: an overview of elementary geochemistry[J]. Sedimentary Geology and Tethyan Geology, 2012, 32(2): 76-88. https://www.cnki.com.cn/Article/CJFDTOTAL-TTSD201202013.htm [30] BENNETT W W, CANFIELD D E. Redox-sensitive trace metals as paleoredox proxies: a review and analysis of data from modern sediments[J]. Earth-Science Reviews, 2020, 204: 103175. doi: 10.1016/j.earscirev.2020.103175 [31] TOSTEVIN R, SHIELDS G A, TARBUCK G M, et al. Effective use of cerium anomalies as a redox proxy in carbonate-dominated marine settings[J]. Chemical Geology, 2016, 438: 146-162. doi: 10.1016/j.chemgeo.2016.06.027 [32] BOYLE E A, SCLATER F R, EDMOND J M. The distribution of dissolved copper in the Pacific[J]. Earth and Planetary Science Letters, 1977, 37(1): 38-54. doi: 10.1016/0012-821X(77)90144-3 [33] BRAND U, VEIZER J. Chemical diagenesis of a multicomponent carbonate system—1: trace elements[J]. Journal of Sedimentary Petrology, 1980, 50(4): 1219-1236. [34] MOLENAAR N, DE JONG A F M. Authigenic quartz and albite in Devonian limestones: origin and significance[J]. Sedimento-logy, 1987, 34(4): 623-640. [35] ZHANG Bolin, CAO Jian, MU Lan, et al. The Permian chert event in South China: new geochemical constraints and global implications[J]. Earth-Science Reviews, 2023, 244: 104513.