Carbon and oxygen isotopic characteristics of karst fracture-cavity fillings and environmental significance: A case study of Ordovician Yingshan Formation in Tahe oilfield
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摘要: 塔河油田奥陶系鹰山组岩溶缝洞是该地区主要的碳酸盐岩储层,弄清岩溶缝洞充填物特征有利于寻找最优储集体,对该区石油地质研究具有重要意义。通过对塔河油田31口钻井岩心观察、描述和充填物类型统计,选取7口典型钻井奥陶系鹰山组岩溶缝洞充填物取样,并对充填物样品δ13C和δ18O进行测试分析。结果表明:(1)充填物碳氧同位素变化范围较大,δ13C为0.75‰~−10.14‰,δ18O为−5.94‰~−14.14‰。(2)奥陶系鹰山组岩溶缝洞充填物存在4中不同类型的形成环境:同生期或早期成岩岩溶环境、风化壳岩溶环境、埋藏岩溶环境、较晚期岩溶环境。该研究成果对古岩溶型油气储层研究及油气勘探具有重要意义。Abstract:
Karst fracture-cavity of Ordovician Yingshan Formation is the main carbonate reservoir in Tahe oilfield. The development of karst fracture-cavity shows strong heterogeneity. The complex diversification of filling types, types of filling materials and filling characteristics leads to the complexity of karst fracture-cavity reservoirs, which has a direct impact on the development of oil reservoirs. Understanding the characteristics of karst fracture-cavity filling is conducive to finding the optimal reservoir, which is of great significance to the study of petroleum geology in this area. In this study, the Ordovician Yingshan Formation cores from several wells in Tahe oilfield were observed, and the karst fracture-cavity fillings and limestone bedrock of typical drilling of Yingshan Formation were collected. Combined with the characteristics of fracture-cavity filling, the carbon and oxygen isotope characteristics are analyzed, and the sedimentary paleoenvironment is clarified, which provides a new geochemical basis for inversion of reservoir formation process. Based on the core observation, description and filling type statistics of 31 drillings in Tahe oilfield, it is found that the fillings of karst fracture-caves of Ordovician Yingshan Formation in Tahe area are mainly characterized by mechanical fillings and chemical deposits, followed by slump fillings. The slump fillings mainly filling in caves and seven boreholes—A8, T615, T502, S64, S70, T403 and T624—can show the most typical characteristics. We collected 35 filling samples of the karst fracture-cavity in these seven typical drillings of Ordovician Yingshan Formation, including calcareous argillaceous, sandy, calcite, breccia and limestone bedrock filled in the dissolution pores. Then, we tested and analyzed δ13C and δ18O of the filling samples. The results show that the variation range of carbon and oxygen isotopes of the backfill is large, with δ13C from 0.75 ‰ to −10.14 ‰ and δ18O from −5.94 ‰ to −14.14 ‰. Compared with the carbon and oxygen isotope of bedrock, the values of δ13C and δ18O of 80% of the backfill are negative, and the calcite is the most negative. The values of δ13C and δ18O of calcium mud filling were significantly positive. There are four different types of formation environment for karst fracture-cavity fillings in Ordovician Yingshan Formation. The first type is the contemporaneous or early diagenetic karst environment. The δ13C and δ18O of the karst fracture-cavity fillings are from −2.29‰ to 0.75‰ and from −5.94‰ to −8.57‰, respectively, which are similar to the carbon and oxygen isotope characteristics of the marine limestone of the Yingshan Formation. This finding indicates that the fracture-cavity fillings are formed in the contemporaneous or early diagenetic marine karst environment, which may be the result of the joint filling of mud carried by flowing water and carbonate rock deposition in the contemporaneous karst period. The second type is Late Caledonian-Early Hercynian weathering crust karst, with the most obvious negative values of carbon and oxygen isotopes: δ13C from −10.14‰ to −8.57 ‰, and δ18O from −14.14‰ to −13.44 ‰, respectively. The negative δ18O value is mainly caused by the low δ18O value of atmospheric freshwater, which leads to the negative δ18O value of precipitated calcite. There are two main reasons for the negative δ13C value. One is the exposure environment of late Caledonian-early Hercynian affected by low δ13C CO2 in atmospheric fresh water, and the negative δ13C value of calcite precipitated after reaction with carbonate rocks. The other is that the content of organic matter overlying on the weathering crust in the Silurian clastic strata is high, and the δ13C value is low due to the oxidation of CH4 by organic matter. The third type is buried karst environment. Both the negative values of δ13C (from −6.54‰ to −3.07‰) and δ18O (from −13.11‰ to −12.43‰) indicate that the fillings are affected by different degrees of atmospheric freshwater in buried karst environment. The fourth type is the late to modern karst environment. The values of δ13C (from −5.24‰ to −0.79‰) and δ18O (from −11.15‰ to −8.77‰) are quite different from those of the carbon and oxygen isotopes in terms of bedrock background values. Most of the filling materials are calcareous argillaceous mechanical filling, mainly filling in karst caves and dissolved structural joints. The filling process is slow and long, and is affected by organic matter to varying degrees. Karst fracture-cavity filling are the product of the formation of karst reservoir in the transformation process. The analysis of carbon and oxygen isotopes of carbonate rocks and karst fracture-cavity fillings is one of the important means for the study of paleokarst oil and gas reservoirs. It is helpful to understand the formation environment, development and evolution of karst and its relationship with the development of oil and gas reservoirs, which is of great significance for the prediction of karst reservoirs and oil and gas exploration. -
表 1 样品信息和δ13C、δ18O测试结果
Table 1. Sample information and test results of δ13C and δ18O
序号 样品编号 地层 δ13C(V-PDB) δ18O(V-PDB) 岩性 ‰ ‰ 1 AD8-1(25/30) O1y 0.17 −5.94 洞顶缝钙泥质充填物 2 AD8-2(14/46) O1y 0.75 −7.03 溶洞顶部充填的灰绿色钙泥 3 AD8-2(37/46) O1y −3.15 −9.12 溶洞内钙质泥岩 4 S64-1(20/20) O1y −1.42 −7.63 灰岩(基岩) 5 S64-2(30/60) O1y −1.35 −9.43 溶洞钙泥质 6 S64-2(40/60) O1y −1.57 −8.77 溶缝钙华 7 S64-6(34/37) O1y −0.79 −9.05 泥晶砂屑灰岩 8 S70-12(6/71) O1y −0.9 −7.22 钙质泥 9 S70-13(13/26) O1y −3.23 −9.99 钙质泥 10 S70-14(2/29) O1y −1.39 −6.52 泥晶灰岩(基岩) 11 T403-1(3/60) O1y −1.12 −7.66 钙泥质 12 T403-4(59/66) O1y −0.97 −7.11 灰岩(基岩) 13 T403-6(27/36) O1y −4.41 −9.84 钙泥质 14 T403-7(20/44) O1y −2.29 −7.89 钙泥质 15 T403-7(23/44) O1y −1.72 −10.23 钙泥质 16 T403-8(14/44) O1y −1.13 −7.93 泥晶灰岩(基岩) 17 T403-8(30/44) O1y −2.45 −10.56 钙泥质 18 T403-8(42/44) O1y −1.56 −8.44 钙泥质 19 T502-14(22/44) O1y −4.55 −9.34 角砾 20 T502-14(23/44) O1y −0.83 −7.64 溶洞底部灰岩角砾 21 T502-14(4/44) O1y −3.39 −9.6 钙泥质 22 T502-14(8/44) O1y −5.24 −11.15 钙泥质 23 T502-15(3/32) O1y −0.83 −8.21 斑状泥晶灰岩(基岩) 24 T615-10(21/33) O1y −3.07 −12.43 溶洞充填钙泥质砂岩 25 T615-11(26/36) O1y −3.32 −10.81 砂岩 26 T615-11(29/36) O1y −0.5 −7.11 洞底角砾 27 T615-7(10/35) O1y −4.72 −10.86 溶洞充填钙泥 28 T615-8(4/33) O1y −5.62 −8.14 缝壁方解石 29 T615-7(9/35) O1y −0.12 −7.75 缝壁微晶灰岩(基岩) 30 T615-9(13/74) O1y −3.21 −9.46 溶洞充填泥质粉砂岩 31 T624-5(5/32) O1y −4.33 −12.69 斜缝方解石 32 T624-6(12/31) O1y −10.14 −13.87 方解石 33 T624-6(18/31) O1y −6.45 −13.11 方解石 34 T624-6(2/31) O1y −8.94 −14.14 方解石 35 T624-6(3/31) O1y −8.57 −13.44 斜缝方解石 36 T502-10(21/44) O1y −0.34 −8.57 硅质团块 37 T502-10(44/44) O1y −1.59 −10.72 硅质团块 38 T502-9(26/40) O1y −1.41 −8.23 硅质团块 表 2 岩溶缝洞充填物及基岩同位素特征
Table 2. Isotope characteristic of karst fracture-cavity fillings and bed rock
发育期次 形成环境 同位素特征 δ13C(PDB)‰ δ18O(PDB)‰ Ⅰ 同生期或早成
岩岩溶环境−2.29~0.75 −5.94~−8.57 Ⅱ 加里东晚期-海西
早期风化壳岩溶−10.14~−8.57 −14.14~−13.44 Ⅲ 埋藏岩溶环境 −6.54~−3.07 −13.11~−12.43 Ⅳ 较晚期-现代岩溶 −5.24~−0.79 −11.15~−8.77 -
[1] 胡向阳, 权莲顺, 齐得山, 侯加根. 塔河油田缝洞型碳酸盐岩油藏溶洞充填特征[J]. 特种油气藏, 2014, 21(1):18-21. doi: 10.3969/j.issn.1006-6535.2014.01.004HU Xiangyang, QUAN Lianshun, QI Deshan, HOU Jiagen. Features of cavern filling in fractured/vuggy carbonate oil reservoirs, Tahe oilfield[J]. Special Oil & Gas Reservoirs, 2014, 21(1):18-21. doi: 10.3969/j.issn.1006-6535.2014.01.004 [2] 漆立新, 云露. 塔河油田奥陶系碳酸盐岩岩溶发育特征与主控因素[J]. 石油与天然气地质, 2010, 31(1):1-12.QI Lixin, YUN Lu. Development characteristics and main controlling factors of the Ordovician carbonate karst in Tahe oilfield[J]. Oil & Gas Geology, 2010, 31(1):1-12. [3] 苏江玉, 俞仁莲. 对塔河油田油气成藏地质研究若干问题的思考[J]. 石油实验地质, 2011, 33(2):105-112. doi: 10.3969/j.issn.1001-6112.2011.02.001SU Jiangyu, YU Renlian. Discussion of several problems in petroleum accumulation geologic research in Tahe oil field[J]. Petroleum Geology & Experiment, 2011, 33(2):105-112. doi: 10.3969/j.issn.1001-6112.2011.02.001 [4] 鲁新便, 高博禹, 陈姝媚. 塔河油田下奥陶统碳酸盐岩古岩溶储层研究:以塔河油田6区为例[J]. 矿物岩石, 2003, 23(1):87-92.LU Xinbian, GAO Boyu, CHEN Shumei. Study on characteristics of paleokarst reservoir in lower Ordovician carbonate of Tahe oil field[J]. Journal of Mineralogy and Petrology, 2003, 23(1):87-92. [5] 张文博, 邵珠福, 张英敏, 田飞, 康逊, 李志诚. 塔河油田奥陶系古溶洞充填砂岩发育特征及成因:以塔河七区T615井为例[J]. 海相油气地质, 2014, 19(1):51-60. doi: 10.3969/j.issn.1672-9854.2014.01.007ZHANG Wenbo, SHAO Zhufu, ZHANG Yingmin, TIAN Fei, KANG Xun, LI Zhicheng. Development characteristics and genesis of filling sandstone in Ordovician paleocaves in Tahe oil field, Tarim Basin: A typical case of filling sandstone in well T615 in Tahe block 7[J]. Marine Origin Petroleum Geology, 2014, 19(1):51-60. doi: 10.3969/j.issn.1672-9854.2014.01.007 [6] 张正红, 淡永, 梁彬, 张庆玉, 李景瑞, 郝彦珍. 塔中Ⅱ区鹰山组岩溶缝洞充填物碳氧同位素特征及环境意义[J]. 中国岩溶, 2015, 34(2):159-164.ZHANG Zhenghong, DAN Yong, LIANG Bin, ZHANG Qingyu, LI Jingrui, HAO Yanzhen. Characteristics of oxygen and carbon isotopes of karst fissure-cave fillings in the Yingshan Formation, Tazhong Ⅱ area, Tarim Basin and their implications for environment[J]. Carsologica Sinica, 2015, 34(2):159-164. [7] 钱一雄, 陈跃, 马宏强, 陈强路. 新疆塔河油田奥陶系碳酸盐岩溶洞、裂隙中方解石胶结物元素分析与成因[J]. 沉积学报, 2004, 22(1):6-12. doi: 10.3969/j.issn.1000-0550.2004.01.002QIAN Yixiong, CHEN Yue, MA Hongqiang, CHEN Qianglu. Chemical analysis and origin of calcite filled in and cave with in Ordovician carbonates in Tahe oilfield, Xinjiang[J]. Acta Sedimentologica Sinica, 2004, 22(1):6-12. doi: 10.3969/j.issn.1000-0550.2004.01.002 [8] 淡永, 梁彬, 曹建文, 张庆玉. 塔里木盆地轮南地区奥陶系岩溶缝洞充填物地球化学特征及环境意义[J]石油实验地质. 2012, 34(6): 623-628.DAN Yong, LIANG Bin, CAO Jianwen, ZHANG Qingyu. Geochemical features and environmental significances of deposits in Ordovician karstic fractures and caves, Lunnan area, Tarim Basin[J]. Petroleum Geology & Experiment. 2012, 34(6): 623-628. [9] 赵万飞, 刘惠果, 王甘露, 苏杭, 张峰玮, 卞华鹏. 于奇西地区奥陶系储层裂缝充填物碳氧同位素地球化学特征[J]. 贵州大学学报(自然科学版), 2012, 29(3): 34-38, 43.ZHAO Wanfei, LIU Huiguo, WANG Ganlu, SU Hang, ZHANG Fengwei, BIAN Huapeng. C and O isotope geochemical characteristics of reservoir crevice fillings in Ordovician, Yuqi west area[J]. Journal of Guizhou University (Natural Sciences), 2012, 29(3): 34-38, 43. [10] 孔兴功. 石笋碳氧同位素古气候代用指标研究进展[J]. 高校地质学报, 2009, 15(2):165-170.KONG Xinggong. Advance in study of oxygen and carbon isotope variations in cave stalagmites as palaeo-climate proxies[J]. Geological Journal of China Universities, 2009, 15(2):165-170. [11] 金强, 田飞, 鲁新便, 康逊. 塔河油田奥陶系古径流岩溶带垮塌充填特征[J]. 石油与天然气地质, 2015, 36(5): 729-735, 755.JIN Qiang, TIAN Fei, LU Xinbian, KANG Xun. Characteristics of collapse breccias filling in caves of runoff zone in the Ordovician karst in Tahe oilfield, Tarim Basin[J]. Oil & Gas Geology, 2015, 36(5): 729-735, 755. [12] 康逊. 塔河油田奥陶系岩溶缝洞充填物形成与储集性能研究[D]. 青岛: 中国石油大学(华东), 2014.KANG Xun. Filling of the fracture-cavity space in Ordovician karst reservoirs of the Tahe oilfield and its reservoirs petrophysics[D]. Qingdao: China University of Petroleum (East China), 2014. [13] 张庆玉. 塔里木盆地哈拉哈塘地区奥陶系碳酸盐岩古岩溶发育机理[D]. 武汉: 中国地质大学(武汉), 2018.ZHANG Qingyu. Development mechanism of Ordovician carbonate paleokarst in the Halahatang area of the Tarim Basin[D]. Wuhan: China University of Geosciences (Wuhan), 2018. [14] 朱学稳. 我国灰岩洞穴次生化学沉积物的沉积类型和形态系统[J]. 中国地质科学院院报, 1986(15):137-142.ZHU Xuewen. The type and form system of speleothems in limestone cave in China[J]. Bulletin of the Chinese Academy of Geological Sciences, 1986(15):137-142. [15] 李英菊. 塔河油田奥陶系古岩溶洞穴充填特征及其油气响应[D]. 荆州: 长江大学, 2020.LI Yingju. The fillings and hydrocarbon of Ordovician paleo-caves in Tahe oilfield[D]. Jingzhou: Yangtze University, 2020. [16] 李阳. 塔河油田奥陶系碳酸盐岩溶洞型储集体识别及定量表征[J]. 中国石油大学学报(自然科学版), 2012, 36(1):1-7.LI Yang. Ordovician carbonate fracture-cavity reservoirs identification and quantitative characterization in Tahe oilfield[J]. Journal of China University of Petroleum (Edition of Natural Sciences), 2012, 36(1):1-7. [17] 李阳, 金强, 钟建华, 邹胜章. 塔河油田奥陶系岩溶分带及缝洞结构特征[J]. 石油学报, 2016, 37(3):289-298. doi: 10.7623/syxb201603001LI Yang, JIN Qiang, ZHONG Jianhua, ZOU Shengzhang. Karst zonings and fracture-cave structure characteristics of Ordovician reservoirs in Tahe oilfield, Tarim Basin[J]. Acta Petrolei Sinica, 2016, 37(3):289-298. doi: 10.7623/syxb201603001 [18] 张娟, 鲍典, 杨敏, 何成江, 邓光校, 张慧涛. 塔河油田西部古暗河缝洞结构特征及控制因素[J]. 油气地质与采收率, 2018, 25(4):33-39. doi: 10.13673/j.cnki.cn37-1359/te.2018.04.006ZHANG Juan, BAO Dian, YANG Min, HE Chengjiang, DENG Guangxiao, ZHANG Huitao. Analysis on fracture-cave structure characteristics and its controlling factor of palaeo-subterranean rivers in the western Tahe oilfield[J]. Petroleum Geology and Recovery Efficiency, 2018, 25(4):33-39. doi: 10.13673/j.cnki.cn37-1359/te.2018.04.006 [19] 王大锐. 塔里木盆地中、上奥陶统烃源岩的碳同位素宏观证据[J]. 地质评论, 2000, 46(3):328-334.WANG Darui. Macro-evidence of carbon isotopes for the middle-upper Ordovician source rocks in the Tarim Basin[J]. Geological Review, 2000, 46(3):328-334. [20] 郑永飞, 徐宝龙, 周根陶. 矿物稳定同位素地球化学研究[J]. 地学前缘(中国地质大学, 北京), 2000, 7(2):299-320.ZHENG Yongfei, XU Baolong, ZHOU Gentao. Geochemical studies of stable isotopes in minerals[J]. Earth Science Frontiers, 2000, 7(2):299-320. [21] 张庆玉, 梁彬, 曹建文, 淡永, 李世银, 李景瑞, 郝彦珍. 塔里木盆地轮古7井区以东奥陶系古岩溶储层碳氧同位素地球化学特征研究[J]. 地质科技情报, 2015, 34(2):52-56.ZHANG Qingyu, LIANG Bin, CAO Jianwen, DAN Yong, LI Shiyin, LI Jingrui, HAO Yanzhen. Research of geochemistry characteristics of carbon and oxygen isotopes of Ordovician paleokarst reservoir in the east of Lungu-7, north Tarim Basin[J]. Geological Science and Technology Information, 2015, 34(2):52-56. [22] 许微, 蔡忠贤, 林忠民, 贾振远. 塔河油田奥陶系碳酸盐岩油藏岩溶成因类型[J]. 海相油气地质, 2012, 17(1):66-72.XU Wei, CAI Zhongxian, LIN Zhongmin, JIA Zhenyuan. Karst genesis classification of Ordovician carbonate reservoir in Tahe oilfield, Tarim Basin[J]. Marine Origin Petroleum Geology, 2012, 17(1):66-72. [23] 钱一雄, 陈强路, 陈跃, 罗月明. 碳酸盐岩中缝洞方解石成岩环境的矿物地球化学判识: 塔河油田的沙79井和沙85井为例[J]. 沉积学报, 2009, 27(6): 1027-1032.QIAN Yixiong, CHEN Qianglu, CHEN Yue, LUO Yueming. Mineralogical and geochemical identification for diagenetic settings of paleo-caves and fractures-filling & vugs calcites in carbonate: Taking wells S79 and S85 for example[J]. Acta Sedimentologica Sinica, 2009, 27(6): 1027-1032. [24] 刘存革, 李国蓉, 朱传玲, 刘国勇, 卢宇峰. 塔河油田中下奥陶统岩溶缝洞方解石碳、氧、锶同位素地球化学特征[J]. 地球科学(中国地质大学学报), 2008(3):377-386. doi: 10.3321/j.issn:1000-2383.2008.03.012LIU Cunge, LI Guorong, ZHU Chuanling, LIU Guoyong, LU Yufeng. Geochemistry characteristics of carbon, oxygen and strontium isotopes of calcites filled in karstic fissure-cave in lower-middle Ordovician of Tahe oilfield, Tarim Basin[J]. Earth Science (Journal of China University of Geosciences), 2008(3):377-386. doi: 10.3321/j.issn:1000-2383.2008.03.012 [25] 金强, 康逊, 田飞. 塔河油田奥陶系古岩溶径流带缝洞化学充填物成因和分布[J]. 石油学报, 2015, 36(7):791-798. doi: 10.1038/aps.2015.26JIN Qiang, KANG Xun, TIAN Fei. Genesis of chemical fillings in fracture-caves in paleo-karst runoff zone in Ordovician and their distributions in Tahe oilfield, Tarim Basin[J]. Acta Petrolei Sinica, 2015, 36(7):791-798. doi: 10.1038/aps.2015.26 [26] 王钊, 邱军利. 鄂尔多斯盆地长8储层碳酸盐岩胶结物成分组成与碳氧同位素特征研究[J]. 油气藏评价与开发, 2018, 8(2):14-21.WANG Zhao, QIU Junli. Study on composition, carbon and oxygen isotopic characteristics of carbonate cements in Chang-8 reservoir, Ordos Basin[J]. Reservoir Evaluation and Development, 2018, 8(2):14-21. [27] 张庆玉, 梁彬, 秦凤蕊, 曹建文, 淡永, 李景瑞. 塔里木盆地奥陶系古潜山碳酸盐岩岩溶储层评价与预测:以轮古7井区以东为例[J]. 中国岩溶, 2017, 36(1):32-41. doi: 10.11932/karst20170104ZHANG Qingyu, LIANG Bin, QIN Fengrui, CAO Jianwen, DAN Yong, LI Jingrui. Evaluation and prediction of carbonate karst reservoirs in the Ordovician buried hills beneath the Tarim Basin: An example east of the Lungu7 well block[J]. Carsologica Sinica, 2017, 36(1):32-41. doi: 10.11932/karst20170104 [28] 张三, 金强, 程付启, 孙建芳, 魏荷花, 张旭栋. 古岩溶流域内地表河与地下河成因联系与储层特征:以塔河油田奥陶系岩溶为例[J]. 中国岩溶, 2020, 39(6):900-910.ZHANG San, JIN Qiang, CHENG Fuqi, SUN Jianfang, WEI Hehua, ZHANG Xudong. Genesis relation of surface and underground rivers and reservoir characteristics in paleokarst drainage systems: A case study of Ordovician karst in the Tahe oilfield[J]. Carsologica Sinica, 2020, 39(6):900-910. [29] 梁乘鹏, 淡永, 徐胜林, 李富祥, 庞春雨, 魏家琦. 塔里木盆地新垦地区奥陶系层间岩溶储层形成机制与控制因素[J]. 中国岩溶. 2019, 38(3): 427-437.LIANG Chengpeng, DAN Yong, XU Shenglin, LI Fuxiang, PANG Chunyu, WEI Jiaqi. Interlayer karst reservoir characteristics and development controlling factors of Ordovician in the Xinken area, Tarim Basin[J]. Carsologica Sinica. 2019, 38(3): 427-437. [30] 刘显凤, 蔡忠贤. 塔河油田溶洞充填物的元素地球化学特征及环境意义[J]. 地质科技情报, 2009, 28(3):53-57.LIU Xianfeng, CAI Zhongxian. Element geochemistry characteristics of karstic cave deposit in Tahe oilfield and its environmental significance[J]. Geological Science and Technology Information, 2009, 28(3):53-57.