莺歌海凹陷东斜坡L气田天然气成因及运移模式
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摘要
基于天然气组成、轻烃和同位素数据以及相关地质资料,对莺歌海凹陷东斜坡L岩性圈闭气田天然气的成因类型、来源以及运移进行研究。结果显示,L气田天然气组成变化较大,烃类含量为33.6%～91.5%,CO_2含量为0.5%～62.2%,干燥系数达0.94～0.99;烷烃气的δ~(13)C1值为-40.71‰～-27.40‰、δ~(13)C2值为-27.27‰～-20.26‰,C5—C7轻烃内组成的异构烷烃含量为55%～73%,属于煤型气,主要来自中新统陆源富有机质烃源岩;当CO_2在天然气中的含量大于10%时,其δ~(13)CCO_2值为-9.04‰～-0.95‰,与之伴生的氦气~3He/~4He值为7.78×10~(-8),属壳源无机成因,深部地层钙质泥岩及碳酸盐岩等热分解生成的CO_2是其主要来源。天然气存在3种运移方式:储集层邻近的中新统烃源岩接触式供烃、中新统梅山组—三亚组烃源岩生成高成熟气通过隐伏断裂垂向充注、沿砂体侧向运移;较大的"源-储"压差是重要的运移驱动力,短距离运移及有效的"源-储"配置控制天然气分布。图12表1参30
Based on the chemical and stable carbon isotopic composition of natural gas and light hydrocarbons, along with regional geological data, the genetic type, origin and migration of natural gases in the L lithologic gas field, the eastern slope of Yinggehai Sag were investigated. The results show that these gases have a considerable variation in chemical composition, with 33.6%–91.5%hydrocarbon, 0.5%–62.2% CO_2, and dryness coefficients ranging from 0.94 to 0.99. The alkane gases are characterized by δ~(13) C1 values of –40.71‰ – –27.40‰, δ~(13) C2 values of –27.27‰ – –20.26‰, and the isoparaffin contents accounting for 55%–73% of the total C5–C7 light hydrocarbons. These data indicate that the natural gases belong to the coal-type gas and are mainly derived from the Miocene terrigenous organic-rich source rocks. When the CO_2 contents are greater than 10%, the δ~(13) CCO_2 values are –9.04‰ to – 0.95‰ and the associated helium has a 3 He/4 He value of 7.78×10~(-8), suggesting that the CO_2 here is crustal origin and inorganic and mainly sourced from the thermal decomposition of calcareous mudstone and carbonate in deep strata. The gas migrated in three ways, i.e., migration of gas from the Miocene source rock to the reservoirs nearby; vertical migration of highly mature gas from deeper Meishan and Sanya Formations source rock through concealed faults; and lateral migration along permeable sandbodies. The relatively large pressure difference between the "source" and "reservoir" is the key driving force for the vertical and lateral migration of gas. Short-distance migration and effective "source-reservoir" match control the gas distribution.
Based on the chemical and stable carbon isotopic composition of natural gas and light hydrocarbons, along with regional geological data, the genetic type, origin and migration of natural gases in the L lithologic gas field, the eastern slope of Yinggehai Sag were investigated. The results show that these gases have a considerable variation in chemical composition, with 33.6%–91.5%hydrocarbon, 0.5%–62.2% CO_2, and dryness coefficients ranging from 0.94 to 0.99. The alkane gases are characterized by δ~(13) C1 values of –40.71‰ – –27.40‰, δ~(13) C2 values of –27.27‰ – –20.26‰, and the isoparaffin contents accounting for 55%–73% of the total C5–C7 light hydrocarbons. These data indicate that the natural gases belong to the coal-type gas and are mainly derived from the Miocene terrigenous organic-rich source rocks. When the CO_2 contents are greater than 10%, the δ~(13) CCO_2 values are –9.04‰ to – 0.95‰ and the associated helium has a 3 He/4 He value of 7.78×10~(-8), suggesting that the CO_2 here is crustal origin and inorganic and mainly sourced from the thermal decomposition of calcareous mudstone and carbonate in deep strata. The gas migrated in three ways, i.e., migration of gas from the Miocene source rock to the reservoirs nearby; vertical migration of highly mature gas from deeper Meishan and Sanya Formations source rock through concealed faults; and lateral migration along permeable sandbodies. The relatively large pressure difference between the "source" and "reservoir" is the key driving force for the vertical and lateral migration of gas. Short-distance migration and effective "source-reservoir" match control the gas distribution.
引文
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[26]ROBERTS S J,NUNN J A.Episodic fluid expulsion from geopressured sediments[J].Marine and Petroleum Geology,1995,12(2):195-204.
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[2]HUANG B J,XIAO X M,HU Z L,et al.Geochemistry and episodic accumulation of natural gases from the Ledong gas field in the Yinggehai Basin,offshore South China Sea[J].Organic Geochemistry,2005,36:1689-1702.
[3]HUANG B J,XIAO X M,LI X X.Geochemistry and origins of natural gases in the Yinggehai and Qiongdongnan Basins,Offshore South China Sea[J].Organic Geochemistry,2003,34:1009-1025.
[4]王振峰,裴健翔.莺歌海盆地中深层黄流组高压气藏形成新模式:DF14井钻获强超压优质高产天然气层的意义[J].中国海上油气,2011,23(4):213-217.WANG Zhenfeng,PEI Jianxiang.A new accumulation model of high pressure gas in Huangliu Formation of the middle-deep interval in Yinggehai Basin:The significance of discovering a good-quality gas pay with overpressure and high production in Well DF14[J].China Offshore Oil and Gas,2011,23(4):213-217.
[5]李绪深,裴健翔,李彦丽.莺歌海盆地乐东气田天然气成藏条件及富集模式[J].天然气工业,2013,33(11):16-21.LI Xushen,PEI Jianxiang,LI Yanli.Gas play conditions and accumulation patterns of the Ledong Gas Fields,Yinggehai Basin[J].Natural Gas Industry,2013,33(11):16-21.
[6]谢玉洪,黄保家.南海莺歌海盆地东方13-1高温高压气田特征与成藏机理[J].中国科学:地球科学,2014,44(8):1731-1739.XIE Yuhong,HUANG Baojia.Characteristics and accumulation mechanisms of the Dongfang 13-1 high temperature and overpressured gas field in the Yinggehai Basin,the South China Sea[J].SCIENCE CHINA Earth Sciences,2014,57(11):2799-2807.
[7]HUANG B J,XIAO X M,ZHU W L.Geochemistry,origin and accumulation of CO2 in natural gases of the Yinggehai Basin,offshore South China Sea[J].AAPG Bulletin,2004,88(9):1277-1293.
[8]谢玉洪,李绪深,童传新,等.莺歌海盆地中央底辟带高温高压天然气富集条件、分布规律和成藏模式[J].中国海上油气,2015,27(4):1-12.XIE Yuhong,LI Xushen,TONG Chuanxin,et al.High temperature and high pressure gas enrichment condition,distribution law and accumulation model in central diapir zone of Yinggehai Basin[J].China Offshore Oil and Gas,2015,27(4):1-12.
[9]张建新,党亚云,何小胡,等.莺歌海盆地乐东区峡谷水道成因及沉积特征[J].海洋地质与第四纪地质,2015,35(5):29-36.ZHANG Jianxin,DANG Yayun,HE Xiaohu,et al.Origin and sedimentary characteristics of canyon channels in Ledong Aera of Yinggehai Basin[J].Ocean Geology and Quaternary Geology,2015,35(5):29-36.
[10]张建新,袁超,党亚云,等.莺歌海盆地乐东区中深层大型储集体发育特征[J].特种油气藏,2016,23(1):62-66.ZHANG Jianxin,YUAN Chao,DANG Yayun,et al.Development characteristics of large reservoirs in medium deep strata of Ledong area in Yinggehai Basin[J].Special oil gas reservoirs,2016,23(1):62-66.
[11]朱伟林.南海北部大陆边缘盆地天然气地质学[M].北京:石油工业出版社,2007.ZHU Weilin.Natural gas geology of continental margin basin in northern South China Sea[M].Beijing:Petroleum Industrial Press,2007.
[12]张伙兰,裴健翔,张迎朝,等.莺歌海盆地东方区中深层黄流组超压储集层特征[J].石油勘探与开发,2013,40(3):284-293.ZHANG Huolan,PEI Jianxiang,ZHANG Yingzhao,et al.Overpressure reservoirs in the mid-deep Huangliu Formation of the Dongfang area,Yinggehai Basin,South China Sea[J].Petroleum Exploration and Development,2013,40(3):284-293.
[13]杨计海,黄保家,陈殿远.莺歌海盆地坳陷斜坡带低孔特低渗气藏形成条件及勘探潜力[J].中国海上油气,2018,30(1):11-21.YANG Jihai,HUANG Baojia,CHEN Dianyuan.Accumulation condition and exploration potential of low porosity and ultra-low permeability sandstone gas reservoirs on the depression slope belt of Yinggehai Basin[J].China Offshore Oil and Gas,2018,30(1):11-21.
[14]戴金星.天然气碳氢同位素特征和各类天然气鉴别[J].天然气地球科学,1993,4(2/3):1-40.DAI Jinxing.Carbon and hydrogen isotope characteristics of natural gas and identification of various genetic gases[J].Natural Gas Geoscience,1993,4(2/3):1-40.
[15]戴金星.中国煤成大气田及气源[M].北京:科学出版社,2014.DAI Jinxing.Coal-formed large gas fields and their source rocks in China[M].Beijing:Science Press,2014.
[16]BERNER U.Empirical carbon isotope/maturity relationships for gases from algal kerogens and terrigenous organic matter,based on dry,open-system pyrolysis[J].Organic Geochemistry,1996,24(10):947-955.
[17]丁巍伟,庞彦明,胡安平.莺-琼盆地天然气成藏条件及地球化学特征[J].石油勘探与开发,2005,32(4):97-102.DING Weiwei,PANG Yanming,HU Anping.Natural gas accumulation and geochemical characteristics in Yinggehai-Qiongdongnan Basin,South China Sea[J].Petroleum Exploration and Development,2005,32(4):97-102.
[18]CATHLES L M,SCHOELL M.Modeling CO2 generation,migration,and titration in sedimentary basins[J].Geofluids,2010,7(4):441-450.
[19]胡国艺,李剑,李谨,等.判识天然气成因的轻烃指标探讨[J].中国科学:地球科学,2007,37(S2):111-117.HU Guoyi,LI Jian,LI Jin,et al.Preliminary study on the origin identification of natural gas by the parameters of light hydrocarbon[J].SCIENCE CHINA Earth Sciences,2008,51(S1):131-139.
[20]黄合庭,黄保家,黄义文,等.南海西部深水区大气田凝析油成因与油气成藏机制:以琼东南盆地陵水17-2气田为例[J].石油勘探与开发,2017,44(3):380-388.HUANG Heting,HUANG Baojia,HUANG Yiwen,et al.Condensate origin and hydrocarbon accumulation mechanism of the deepwater giant gas field in western South China Sea:A case study of Lingshui17-2 gas field in Qiongdongnan Basin[J].Petroleum Exploration and Development,2017,44(3):380-388.
[21]ZHU W L,HUANG B J,MI L J,et al.Geochemistry,origin and deep-water exploration potential of natural gases in the Pearl River Mouth and Qiongdongnan Basins,South China Sea[J].AAPGBulletin,2009,93(6):741-761.
[22]黄保家,黄合庭,李里,等.莺-琼盆地海相烃源岩特征及高温高压环境有机质热演化[J].海相油气地质,2010,15(3):11-18.HUANG Baojia,HUANG Heting,LI Li,et al.Characteristics of marine source rocks and effect of high temperature and overpressure to organic matter maturation in Yinggehai-Qiongdongnan Basins[J].Marine Origin Petroleum Geology,2010,15(3):11-18.
[23]黄第藩.陆相烃源岩有机质中碳同位素组成的分布特征[J].中国海上油气,1993,7(4):1-5.HUANG Difan.Distributive characteristics of carbon isotope composition in organic matters of continental source rocks[J].China Offshore Oil and Gas,1993,7(4):1-5.
[24]黄保家,肖贤明,董伟良.莺歌海盆地烃源岩特征及天然气生成演化模式[J].天然气工业,2002,22(1):26-30.HUANG Baojia,XIAO Xianming,DONG Weiliang.Source rocks and generation&evolution model of natural gas in Yinggehai Basin[J].Natural Gas Industry,2002,22(1):26-30.
[25]HUNT J M.Generation and migration of petroleum from abnormally pressured fluid compartments[J].AAPG Bulletin,1990,74(1):1-12.
[26]ROBERTS S J,NUNN J A.Episodic fluid expulsion from geopressured sediments[J].Marine and Petroleum Geology,1995,12(2):195-204.
[27]LAW B E,ULMISHEK G F,SLAVIN V I.Abnormal pressure in hydrocarbon environments[M].Tulsa:The American Association of Petroleum Geologist,1998:7-11.
[28]杨计海.莺-琼盆地温压场与天然气运聚关系[J].天然气工业,1999,19(1):39-43.YANG Jihai.Influence of geothermal-geopressure field on the migration and accumulation of natural gas in Yinggehai Basin[J].Natural Gas Industry,1999,19(1):39-43.
[29]马中良,郑伦举,秦建中,等.盆地沉降、抬升过程中源储压差的生排烃效应[J].石油实验地质,2011,33(4):402-407.MA Zhongliang,ZHENG Lunju,QIN Jianzhong,et al.Hydrocarbon generation and expulsion caused by pressure difference between source rock and reservoir during basin subsiding and uplifting[J].Petroleum Geology Experiment,2011,33(4):402-407.
[30]魏国齐,张福东,李君,等.中国致密砂岩气成藏理论进展[J].天然气地球科学,2016,27(2):199-210.WEI Guoqi,ZHANG Fudong,LI Jun,et al.New progress of tight sand gas accumulation theory and favorable exploration zones in China[J].Natural Gas Geoscience,2016,27(2):199-210.