青海木里天然气水合物储层大地电磁法理论模拟分析
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摘要
青海木里地区地质构造复杂,天然气水合物成藏规律不清,为了大地电磁法探测天然气水合物有更好的应用效果,有必要进行大地电磁法理论模拟研究.本文基于青海木里地区的天然气水合物赋存方式,设计了两种天然气水合物地电模型,采用大地电磁法的有限元法正演及非线性共轭梯度法反演计算,重点分析大地电磁法对冻土层、断裂及水合物储层的分辨率及不同极化模式反演对水合物储层的识别效果.理论模拟结果表明:大地电磁法对冻土层、断裂有较好的探测效果;TE模式的反演结果比TM模式的反演结果对水合物储层异常反映更明显;TE+TM模式中降低TE模式的数据误差值,使TE模式的数据在反演过程中权重加大,反演结果也能显示出水合物储层异常.本次的理论模拟结果对探测天然气水合物的大地电磁数据处理有一定借鉴作用.
Region of muli geological structure is complex, gas hydrate accumulation rule is not clear, in order to magnetotelluric method to detect gas hydrate has better application effect, it is necessary for magnetotelluric method theory simulation study.Two hydrate geoelectric models are designed that based on mode of occurrence of terrestrial gas hydrate in Muli area, Qinghai, and making forward and inverse computation to the theoretical models depends on finite element method of the audio frequency magnetotelluric method and nonlinear conjugate gradient method.The results show that the audio frequency magnetotelluric method has good prospecting effects on the permafrost and fault, and make comparative analysis on the prospecting effects of TE,TM and TE+TM mode to the hydrate reservoir,discuss the resolution of the audio frequency magnetotelluric method to the permafrost, fault and the hydrate reservoir.The analysis results show that the TE mode has more unusual reflection than TM mode to the hydrate reservoir, or lower the data error of TE mode in TE+TM mode can bring about larger weight of the data in TE mode in the inversion procedure,the inversion results can also show the abnormity of the hydrate reservoir.This theoretical simulation has directive role on the audio frequency magnetotelluric data processing of the gas hydrate.
Region of muli geological structure is complex, gas hydrate accumulation rule is not clear, in order to magnetotelluric method to detect gas hydrate has better application effect, it is necessary for magnetotelluric method theory simulation study.Two hydrate geoelectric models are designed that based on mode of occurrence of terrestrial gas hydrate in Muli area, Qinghai, and making forward and inverse computation to the theoretical models depends on finite element method of the audio frequency magnetotelluric method and nonlinear conjugate gradient method.The results show that the audio frequency magnetotelluric method has good prospecting effects on the permafrost and fault, and make comparative analysis on the prospecting effects of TE,TM and TE+TM mode to the hydrate reservoir,discuss the resolution of the audio frequency magnetotelluric method to the permafrost, fault and the hydrate reservoir.The analysis results show that the TE mode has more unusual reflection than TM mode to the hydrate reservoir, or lower the data error of TE mode in TE+TM mode can bring about larger weight of the data in TE mode in the inversion procedure,the inversion results can also show the abnormity of the hydrate reservoir.This theoretical simulation has directive role on the audio frequency magnetotelluric data processing of the gas hydrate.
引文
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Song H B,Jiang W W,Zhang W S,et al. 2002. Progress on marine geophysical studies of gas hydrates[J]. Progress in Geophysics (in chinese),17(2): 224-229,doi: 10.3969/j.issn.1004-2903.2002.02.006.宋海斌,江为为,张文生,等. 2002. 天然气水合物的海洋地球物理研究进展[J]. 地球物理学进展,17(2): 224-229,doi: 10.3969/j.issn.1004-2903.2002.02.006.
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Tang J T,Wang Y,Du H K,et al. 2009. A study of high frequency magnetotelluric numerical modeling by finite element method[J]. Computing Techniques for Geophysical and Geochemical Exploration (in Chinese),(04): 297-302.汤井田,王烨,杜华坤,等. 2009. 高频大地电磁法有限元数值模拟[J]. 物探化探计算技术,(04): 297-302.
Weng A H,Zhu S A. 2010. Near sea-bottom DC sounding response for gas hydrate[J]. Oil Geophysical Prospecting (in Chinese),45(3): 458- 461.翁爱华,祝嗣安. 2010. 天然气水合物的近海底直流电测深响应[J]. 石油地球物理勘探,45(3): 458- 461.
Xu K J,Li T L,Zhang H,et al. 2006. Three dimensional magnetotelluric forward modeling using integral equation[J]. Northwestern Seismological Journal (in Chinese),(02): 104-107.徐凯军,李桐林,张辉,等. 2006. 利用积分方程法的大地电磁三维正演[J]. 西北地震学报,(02): 104-107.
Yuan J,Edwards R N. 2000. The assessment of marine gas hydrate through electrical remote sounding: Hydrate without a BSR[J]. Geophysical Research Letters,27(16): 2397-2400.
Zhai G Y,Lu Z Q,Lu H L,et al. 2014. Gas hydrate geological system in the qilian moutain permafrost[J]. Mineral Petrol (in Chinese),(04): 79-92.翟刚毅,卢振权,卢海龙,等. 2014. 祁连山冻土区天然气水合物成矿系统[J]. 矿物岩石,(04): 79-92.
Zhang S Y,Yang M X,Luo Y Z. 2004. Research on Transient electromagnetic response of gas hydrate[J]. Oil Geophysical Prospecting (in Chinese),39(S1): 62- 65+169.张胜业,杨梅霞,罗延钟. 2004. 天然气水合物的瞬变电磁响应研究[J]. 石油地球物理勘探,39(S1): 62- 65+169.
Zhu Y H,Zhang Y Q,Wen H J,et al. 2009. Gas hydrates in the Qilian Moutain permafrost,Qinghai,Northwest China[J]. Acta Geologica Sinica (in Chinese),83(11): 1762-1771.祝有海,张永勤,文怀军,等. 2009. 青海祁连山冻土区发现天然气水合物[J]. 地质学报,83(11): 1762-1771.
Zhu Y H,Zhang Y Q,Wen H J,et al. 2010. Gas hydrate in Qilian mountain permafrost and their basic characteristic[J]. Acta Geoscientica Sinica (in Chinese),31(1): 7-16.祝有海,张永勤,文怀军,等. 2010. 祁连山冻土区天然气水合物及其基本特征[J]. 地球学报,31(1): 7-16.
Chen J W,Yang G J,Wu Z Q,et al. 2004. Geophisical marks of gas hydrate[J]. Marine Geology Letters (in Chinese),20(6): 9-12.陈建文,闫桂京,吴志强,等. 2004. 天然气水合物的地球物理识别标志[J]. 海洋地质动态,20(6): 9-12.
Collett T. S.,Lee M. W.,Agena W. F.,et al. 2011. Permafrost-associated natural gas hydrate occurrences on the Alaska North Slope[J]. Marine and Petroleum Geology,28(2): 279-294.
Edwards R. N. 1997. On the resource evaluation of marine gas hydrate deposits using sea-floor transient electric dipole-dipole methods[J]. Geophysics,62(1): 63-74.
He M X,Hu X Y,Ye Y X,et al. 2011. 2.5D controlled source audio-frequency magnetotellurics occam inversion[J]. Progress in Geophysics (in Chinese),(06): 2163-2170,doi: 10.3969/j.issn.1004-2903.2011.06.033.何梅兴,胡祥云,叶益信,等. 2011. 2.5维可控源音频大地电磁法Occam反演理论及应用[J]. 地球物理学进展,(06): 2163-2170,doi: 10.3969/j.issn.1004-2903.2011.06.033.
Lin Z Z,Li Y,Gao W L. 2013. Physical character analysis of logging data for natural gas hydrate in qilian moutain permafrost area[J]. Geophysical & Geochemical explortion (in Chinese),(05): 834-838.林振洲,李洋,高文利,等. 2013. 祁连山冻土区天然气水合物层位测井物性分析[J]. 物探与化探,(05): 834-838.
Lu Z Q,Li Y H,Wang W C. 2015. Study on the Accumulation Pattern for Permafrost-associated Gas Hydrate in Sanlutian of Muli,Qinghai[J]. Geoscience (in Chinese),(05): 1014-1023.卢振权,李永红,王伟超,等. 2015. 青海木里三露天冻土天然气水合物成藏模式研究[J]. 现代地质,(05): 1014-1023.
Lu Z Q,Zhai G Y,Wen H J,et al. 2015. Geological Constraints on Gas Hydrate Formation and Distribution in Sanlutian Permafrost of Muli,Qinghai[J]. Geoscience (in Chinese),(05): 1002-1013.卢振权,翟刚毅,文怀军,等. 2015. 青海木里三露天冻土区天然气水合物形成与分布地质控制因素[J].现代地质,(05): 1002-1013.
Lu Z Q,Zhu Y H,Zhang Y Q,et al. 2010. Basic geological characteristics of gas hydrates in Qilian Mountain permafrost area,Qinghai Province[J]. Mineral Deposits (in Chinese),(01): 182-191.卢振权,祝有海,张永勤,等. 2010. 青海省祁连山冻土区天然气水合物基本地质特征[J]. 矿床地质,(01): 182-191.
Rodi W,Mackie R L. 2001. Nonlinear conjugate gradients algorithm for 2-D magnetotelluric inversion[J]. Geophysics,66(1): 174-187.
Song H B,Jiang W W,Zhang W S,et al. 2002. Progress on marine geophysical studies of gas hydrates[J]. Progress in Geophysics (in chinese),17(2): 224-229,doi: 10.3969/j.issn.1004-2903.2002.02.006.宋海斌,江为为,张文生,等. 2002. 天然气水合物的海洋地球物理研究进展[J]. 地球物理学进展,17(2): 224-229,doi: 10.3969/j.issn.1004-2903.2002.02.006.
Tan H D,Yu Q F,John Booker,et al. 2003. Magnetotelluric three dimensional modelling using the staggered-gris finite difference method[J]. Chinese Journal of Geophysics (in Chinese),(05): 706-711,doi: 10.3321/j.issn:0001-5733.2003.05.019.谭捍东,余钦范,John Booker,等. 2003. 大地电磁法三维交错采样有限差分数值模拟[J]. 地球物理学报,(05):705-711,doi: 10.3321/j.issn:0001-5733.2003.05.019.
Tang J T,Wang Y,Du H K,et al. 2009. A study of high frequency magnetotelluric numerical modeling by finite element method[J]. Computing Techniques for Geophysical and Geochemical Exploration (in Chinese),(04): 297-302.汤井田,王烨,杜华坤,等. 2009. 高频大地电磁法有限元数值模拟[J]. 物探化探计算技术,(04): 297-302.
Weng A H,Zhu S A. 2010. Near sea-bottom DC sounding response for gas hydrate[J]. Oil Geophysical Prospecting (in Chinese),45(3): 458- 461.翁爱华,祝嗣安. 2010. 天然气水合物的近海底直流电测深响应[J]. 石油地球物理勘探,45(3): 458- 461.
Xu K J,Li T L,Zhang H,et al. 2006. Three dimensional magnetotelluric forward modeling using integral equation[J]. Northwestern Seismological Journal (in Chinese),(02): 104-107.徐凯军,李桐林,张辉,等. 2006. 利用积分方程法的大地电磁三维正演[J]. 西北地震学报,(02): 104-107.
Yuan J,Edwards R N. 2000. The assessment of marine gas hydrate through electrical remote sounding: Hydrate without a BSR[J]. Geophysical Research Letters,27(16): 2397-2400.
Zhai G Y,Lu Z Q,Lu H L,et al. 2014. Gas hydrate geological system in the qilian moutain permafrost[J]. Mineral Petrol (in Chinese),(04): 79-92.翟刚毅,卢振权,卢海龙,等. 2014. 祁连山冻土区天然气水合物成矿系统[J]. 矿物岩石,(04): 79-92.
Zhang S Y,Yang M X,Luo Y Z. 2004. Research on Transient electromagnetic response of gas hydrate[J]. Oil Geophysical Prospecting (in Chinese),39(S1): 62- 65+169.张胜业,杨梅霞,罗延钟. 2004. 天然气水合物的瞬变电磁响应研究[J]. 石油地球物理勘探,39(S1): 62- 65+169.
Zhu Y H,Zhang Y Q,Wen H J,et al. 2009. Gas hydrates in the Qilian Moutain permafrost,Qinghai,Northwest China[J]. Acta Geologica Sinica (in Chinese),83(11): 1762-1771.祝有海,张永勤,文怀军,等. 2009. 青海祁连山冻土区发现天然气水合物[J]. 地质学报,83(11): 1762-1771.
Zhu Y H,Zhang Y Q,Wen H J,et al. 2010. Gas hydrate in Qilian mountain permafrost and their basic characteristic[J]. Acta Geoscientica Sinica (in Chinese),31(1): 7-16.祝有海,张永勤,文怀军,等. 2010. 祁连山冻土区天然气水合物及其基本特征[J]. 地球学报,31(1): 7-16.