南海北部神狐海域天然气水合物分解的测井异常
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摘要
南海北部神狐海域GMGS-1钻探揭示SH3井天然气水合物位于稳定带上部,厚度约为10m.氯离子异常计算的水合物饱和度最高达26%,高水合物饱和度层出现高电阻率和低纵波速度.为分析该低纵波速度异常,本文基于简化的三相介质理论计算了饱和水纵波速度,在深度195m附近,测量的纵波速度小于饱和水纵波速度.利用阿尔奇公式,基于原位温度、盐度、密度孔隙度和测量的电阻率,利用交会分析确定了该井的阿尔奇常数为a=1.1和m=2.3.基于该参数,利用阿尔奇方程计算的水合物饱和度占孔隙空间5%～20%,局部地层水合物饱和度达26.8%,在垂向上分布不均匀.由于钻探可能导致水合物发生分解而产生游离气,原位游离气和水合物分解产生的气体都能造成低纵波速度异常.由于地震资料采集在测井之前完成,利用不同速度制作合成地震记录并与地震资料进行对比,能够确定水合物稳定带上部的低速异常形成原因.
During the gas hydrate drilling expedition,GMGS-1 indicated that gas hydrate was discovered above the gas hydrate stability zone with a thickness of 10 meters at site SH3 in the Shenhu area,the northern slope of South China Sea.Gas hydrate saturations derived from observed pore-water chloride values in core samples reach the highest value of 26% in the pore space.Higher resistivity,lower P-wave velocity and slightly increasing density were identified.To explain the lower P-wave velocity,the Simplified Three-Phase Biot-type Equation(STPBE) was used to calculate the water-saturated P-wave velocity.At the depth of 195 m,the P-wave velocity from wireline logging is lower than that of the water-saturated velocity of the normal sediments.The Archie′s parameters used to calculate gas hydrate saturation from resistivity were defined from the cross plot between density porosity and formation factor.Gas hydrate saturation estimated from resistivity using Archie equation with a=1.1 and m=2.3 is about 5%~20% of the pore space,with a maximum value of 26.8%,which shows that the distribution of gas hydrate is heterogeneous in vertical.The dissociation of gas hydrate(the mixture of free gas and water) may be caused by drilling.Either the in-situ free gas or gas released from gas hydrate dissociation can cause the low well-log P-wave velocity.Because surface seismic data were acquired before drilling,synthetic seismograms generated using different P-wave velocities were compared with the seismic data,which can be used to identify the cause of the low P-wave velocity observed in the well log.
During the gas hydrate drilling expedition,GMGS-1 indicated that gas hydrate was discovered above the gas hydrate stability zone with a thickness of 10 meters at site SH3 in the Shenhu area,the northern slope of South China Sea.Gas hydrate saturations derived from observed pore-water chloride values in core samples reach the highest value of 26% in the pore space.Higher resistivity,lower P-wave velocity and slightly increasing density were identified.To explain the lower P-wave velocity,the Simplified Three-Phase Biot-type Equation(STPBE) was used to calculate the water-saturated P-wave velocity.At the depth of 195 m,the P-wave velocity from wireline logging is lower than that of the water-saturated velocity of the normal sediments.The Archie′s parameters used to calculate gas hydrate saturation from resistivity were defined from the cross plot between density porosity and formation factor.Gas hydrate saturation estimated from resistivity using Archie equation with a=1.1 and m=2.3 is about 5%~20% of the pore space,with a maximum value of 26.8%,which shows that the distribution of gas hydrate is heterogeneous in vertical.The dissociation of gas hydrate(the mixture of free gas and water) may be caused by drilling.Either the in-situ free gas or gas released from gas hydrate dissociation can cause the low well-log P-wave velocity.Because surface seismic data were acquired before drilling,synthetic seismograms generated using different P-wave velocities were compared with the seismic data,which can be used to identify the cause of the low P-wave velocity observed in the well log.
引文
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[11]Wang X J,Hutchinson D R,Wu S G,et al.Elevated gashydrate saturation within silt and silty clay sediments in theShenhu area,South China Sea.J.Geophys.Res.,2011,116:B05102.
[12]Dvorkin J,Prasad M,Sakai A,et al.Elasticity of marinesediments:Rock physics modeling.Geophys.Res.Lett.,1999,26(12):1781-1784.
[13]Helgerud M B,Dvorkin J,Nur A,et al.Elastic-wavevelocity in marine sediments with gas hydrates:Effectivemedium modeling.Geophys.Res.Lett.,1999,26(13):2021-2024.
[14]Lee M W.Amount of gas hydrate estimated fromcompressional and shear-wave velocities at the JAPEX/JNOC/GSC Mallik 2L-38gas hydrate research well.Bull.Geol.Surv.Can.,1999,544:313-322.
[15]Carcione J M,Tinivella U.Bottom-simulating reflectors:seismic velocities and AVO based on laboratory,well andseismic data.Geophys.Prosp.,2000,49(3):523-539.
[16]Carcione J M,Gei D.Gas-hydrate concentration estimatedfrom P-and S-wave velocities at the Mallik 2L-38researchwell,Mackenzie Delta,Canada.J.Appl.Geophys.,2004,56(1):73-78.
[17]Lee M W,Waite W F.Estimating pore-space gas hydratesaturations from well log acoustic data.Geochem.Geophys.Geosyst.,2008,9(7):Q07008.
[18]Yun T S,Francisca F M,Santamarina J C,et al.Compressional and shear wave velocities in uncementedsediment containing gas hydrate.Geophys.Res.Lett.,2005,32(10):L10609.
[19]Yun T S,Santamarina J C,Ruppel C.Mechanical propertiesof sand,silt,and clay containing tetrahydrofuran hydrate.J.Geophys.Res.,2007,112(B4):B04106.
[20]Kleinberg R L,Flaum C,Collett T S.Magnetic resonancelog of JAPEX/JNOC/GSC et al.Mallik 5L-38gas hydrateproduction research well:Gas hydrate saturation,growthhabit,and relative permeability.//Dallimore S R,Collett TS eds.Scientific Results from the Mallik2002 Gas HydrateProduction Research Well Program,Makenzie Delta,Northwest Territories,Canada.Bull.Geol.Surv.Can.,2005,585:1-10.
[21]Leclaire P,Cohen-Ténoudji F,Aguirre-Puente J.Extensionof Biot′s theory of wave propagation to frozen porous media.J.Acoust.Soc.Am.,1994,96(6):3753-3768.
[22]Briaud J L,Chaouch A.Hydrate melting in soil around hotconductor.J.Geotech.Geoenviron.Eng.,1997,123(7):645-653.
[23]Lee M W,Collett T S.Gas hydrate and free gas saturationsestimated from velocity logs on Hydrate Ridge,offshoreOregon,U.S.A.//Trehu A M,Bohrmann G,Torres ME eds.Proceedings of the Ocean Drilling Program ScientificResults,2006,204:1-25.
[24]Collett T S,Lewis R E,Dallimore S R,et al.Detailedevaluation of gas hydrate reservoir properties using JAPEX/JNOC/GSC Mallik 2L-38gas hydrate research well downholewell-log displays.//Dallimore S R,Uchida T,Collett T Seds.Scientific Results from JAPEX/JNOC/GSC Mallik 2L-38Gas Hydrate Research Well,Mackenzie Delta,NorthwestTerritories,Canada.Bull.Geol.Surv.Can.,1999,544:295-311.
[25]Tinivella U.A method for estimating gas hydrate and freegas concentrations in marine sediments.Bollettino diGeofisica Teorica ed Applicata,1999,40(1):19-30.
[26]Domenico S N.Elastic properties of unconsolidated poroussand reservoirs.Geophysics,1977,42(7):1339-1368.
[27]White J E.Computed seismic speeds and attenuation in rockswith partial gas saturation.Geophysics,1975,40(2):224-232.
[28]Lee M W.Models for gas hydrate-bearing sediments inferredfrom hydraulic permeability and elastic velocities.U.S.Geological Survey Scientific Investigations Report 5219,2008:1-15.
[29]Pride S R,Berryman J G,Harris J M.Seismic attenuationdue to wave-induced flow.J.Geophys.Res.,2004,109(B1):B01201.
[30]Lee M W.Proposed moduli of dry rock and their applicationto predicting elastic velocities of sandstones.U.S.GeologicalSurvey Scientific Investigations Report 2005-5119,2005:1-14.
[31]Mindlin R D.Compliance of elastic bodies in contact.Journalof Applied Mechanics,1949,16:259-268.
[32]陈芳,周洋,苏新等.南海神狐海域含水合物层粒度变化及与水合物饱和度的关系.海洋地质与第四纪地质,2011,31(5):95-100.Chen F,Zhou Y,Su X,et al.Gas hydrate saturation and itsrelation with grain size of the hydrate-bearing sediments inthe Shenhu area of northern South China Sea.MarineGeology&Quaternary Geology(in Chinese),2011,31(5):95-100.
[33]Arp J J.The effect of temperature on the density andelectrical resistivity of sodium chloride solutions.Journal ofPetroleum Technology,1953,5(10):17-20.
[34]Guérin G,Goldberg D,Meltser A.Characterization of in situelastic properties of gas hydrate-bearing sediments on theBlake Ridge.J.Geophys.Res.,1999,104(B8):17781-17795.
[35]Wu N Y,Yang S X,Zhang H Q,et al.Gas hydrate systemof Shenhu area,northern South China Sea:Wire-linelogging,geochemistrical results and preliminary resourcesestimates.OCT,2010,20485,1-13.
[36]Hyndman R D,Spence G D.A seismic study of methanehydrate marine bottom simulating reflectors.J.Geophys.Res.,1992,97(B5):6683-6698.
[37]Minshull T A,Singh S C,Westbrook G K.Seismic velocitystructure at a gas hydrate reflector,offshore westernColombia,from full waveform inversion.J.Geophys.Res.,1994,99(B3):4715-4734.
[38]陆红锋,陈弘,陈芳等.南海神狐海域天然气水合物钻孔沉积物矿物学特征.南海地质研究,2009,20:28-37.Lu H F,Chen H,Chen F,et al.Mineralogy of thesediments from gas-hydrate drilling sites,Shenhu area,South China Sea.Geological Research of South China Sea(in Chinese),2009,20:28-37.
[39]Wang X J,Lee M,Wu S G,et al.Identification of gashydrate dissociation from wireline logs data in the Shenhuarea,South China Sea.Geophysics,2012,77(3):125-134.
[40]Heeschen K U,Tréhu A M,Collier R W,et al.Distributionand height of methane bubble plumes on the Cascadia margincharacterized by acoustic imaging.Geophys.Res.Lett.,2003,30(12):1643-1646.
[41]Gorman A R,Holbrook W S,Hornbach M J,et al.Migration of methane gas through the hydrate stability zonein a low-flux hydrate province.Geology,2002,30(4):327-330.
[42]龚建明,何玉华,闫贵京等.南海“神狐型”BSR特征及影响因素.石油实验地质,2011,33(6):602-606.Gong J M,He Y H,Yan G J,et al.Features and controllingfactors of BSR in Shenhu area,South China Sea.PetroleumGeology&Experiment(in Chinese),2011,33(6):602-606.
[2]Park K P,Bahk J J,Kwon Y,et al.Korean nationalprogram expedition confirm rich gas hydrate deposits in theUlleung Basin,East Sea.DOE-National Energy TechnologyLaboratory(NETL)Fire in the Ice Methane HydrateNewsletter,2008:6-9.
[3]Riedel M,Collett T S,Malone M J,et al.Cascadia margingas hydrates.Proceedings of the Integrated Ocean DrillingProgram 311,2005:1-135.
[4]Zhang H Q,Yang S X,Wu N Y,et al.Successful andsurprising results for China′s first gas hydrate drillingexpedition.Fire in the Ice Methane Hydrate Newsletter,National Energy Technology Laboratory,US Department ofEnergy,2007:6-9.
[5]Tréhu A M,Ruppel C,Holland M,et al.Gas hydrates inmarine sediments:Lessons from scientific ocean drilling.Oceanography,2006,19(4):124-142.
[6]Cook A E,Goldberg D.Extent of gas hydrate filled fractureplanes:Implications for in situ methanogenesis and resourcepotential.Geophys.Res.Lett.,2008,35:L15302.
[7]吴能友,杨胜雄,王宏斌等.南海北部陆坡神狐海域天然气水合物成藏的流体运移体系.地球物理学报,2009,52(6):1641-1650.Wu N Y,Yang S X,Wang H B,et al.Gas-bearing fluidinflux sub-system for gas hydrate geological system in ShenhuArea,Northern South China Sea.Chinese J.Geophys.(inChinese),2009,52(6):1641-1650.
[8]陆敬安,杨胜雄,吴能友等.南海神狐海域天然气水合物地球物理测井评价.现代地质,2008,22(3):447-451.Lu J A,Yang S X,Wu N Y,et al.Well logging evaluationof gas hydrates in Shenhu area,South China Sea.Geoscience(in Chinese),2008,22(3):447-451.
[9]王秀娟,吴时国,刘学伟等.基于测井和地震资料的神狐海域天然气水合物资源量估算.地球物理学进展,2010,25(4):1288-1297.Wang X J,Wu S G,Liu X W,et al.Estimation of gashydrates resources based on well log data and seismic data inShenhu area.Progress in Geophysics(in Chinese),2010,25(4):1288-1297.
[10]梁劲,王明君,陆敬安等.南海神狐海域含水合物地层测井响应特征.现代地质,2010,24(3):506-514.Liang J,Wang M J,Lu J A,et al.Logging responsecharacteristics of gas hydrate formation in Shenhu area of theSouth China Sea.Geoscience(in Chinese),2010,24(3):506-514.
[11]Wang X J,Hutchinson D R,Wu S G,et al.Elevated gashydrate saturation within silt and silty clay sediments in theShenhu area,South China Sea.J.Geophys.Res.,2011,116:B05102.
[12]Dvorkin J,Prasad M,Sakai A,et al.Elasticity of marinesediments:Rock physics modeling.Geophys.Res.Lett.,1999,26(12):1781-1784.
[13]Helgerud M B,Dvorkin J,Nur A,et al.Elastic-wavevelocity in marine sediments with gas hydrates:Effectivemedium modeling.Geophys.Res.Lett.,1999,26(13):2021-2024.
[14]Lee M W.Amount of gas hydrate estimated fromcompressional and shear-wave velocities at the JAPEX/JNOC/GSC Mallik 2L-38gas hydrate research well.Bull.Geol.Surv.Can.,1999,544:313-322.
[15]Carcione J M,Tinivella U.Bottom-simulating reflectors:seismic velocities and AVO based on laboratory,well andseismic data.Geophys.Prosp.,2000,49(3):523-539.
[16]Carcione J M,Gei D.Gas-hydrate concentration estimatedfrom P-and S-wave velocities at the Mallik 2L-38researchwell,Mackenzie Delta,Canada.J.Appl.Geophys.,2004,56(1):73-78.
[17]Lee M W,Waite W F.Estimating pore-space gas hydratesaturations from well log acoustic data.Geochem.Geophys.Geosyst.,2008,9(7):Q07008.
[18]Yun T S,Francisca F M,Santamarina J C,et al.Compressional and shear wave velocities in uncementedsediment containing gas hydrate.Geophys.Res.Lett.,2005,32(10):L10609.
[19]Yun T S,Santamarina J C,Ruppel C.Mechanical propertiesof sand,silt,and clay containing tetrahydrofuran hydrate.J.Geophys.Res.,2007,112(B4):B04106.
[20]Kleinberg R L,Flaum C,Collett T S.Magnetic resonancelog of JAPEX/JNOC/GSC et al.Mallik 5L-38gas hydrateproduction research well:Gas hydrate saturation,growthhabit,and relative permeability.//Dallimore S R,Collett TS eds.Scientific Results from the Mallik2002 Gas HydrateProduction Research Well Program,Makenzie Delta,Northwest Territories,Canada.Bull.Geol.Surv.Can.,2005,585:1-10.
[21]Leclaire P,Cohen-Ténoudji F,Aguirre-Puente J.Extensionof Biot′s theory of wave propagation to frozen porous media.J.Acoust.Soc.Am.,1994,96(6):3753-3768.
[22]Briaud J L,Chaouch A.Hydrate melting in soil around hotconductor.J.Geotech.Geoenviron.Eng.,1997,123(7):645-653.
[23]Lee M W,Collett T S.Gas hydrate and free gas saturationsestimated from velocity logs on Hydrate Ridge,offshoreOregon,U.S.A.//Trehu A M,Bohrmann G,Torres ME eds.Proceedings of the Ocean Drilling Program ScientificResults,2006,204:1-25.
[24]Collett T S,Lewis R E,Dallimore S R,et al.Detailedevaluation of gas hydrate reservoir properties using JAPEX/JNOC/GSC Mallik 2L-38gas hydrate research well downholewell-log displays.//Dallimore S R,Uchida T,Collett T Seds.Scientific Results from JAPEX/JNOC/GSC Mallik 2L-38Gas Hydrate Research Well,Mackenzie Delta,NorthwestTerritories,Canada.Bull.Geol.Surv.Can.,1999,544:295-311.
[25]Tinivella U.A method for estimating gas hydrate and freegas concentrations in marine sediments.Bollettino diGeofisica Teorica ed Applicata,1999,40(1):19-30.
[26]Domenico S N.Elastic properties of unconsolidated poroussand reservoirs.Geophysics,1977,42(7):1339-1368.
[27]White J E.Computed seismic speeds and attenuation in rockswith partial gas saturation.Geophysics,1975,40(2):224-232.
[28]Lee M W.Models for gas hydrate-bearing sediments inferredfrom hydraulic permeability and elastic velocities.U.S.Geological Survey Scientific Investigations Report 5219,2008:1-15.
[29]Pride S R,Berryman J G,Harris J M.Seismic attenuationdue to wave-induced flow.J.Geophys.Res.,2004,109(B1):B01201.
[30]Lee M W.Proposed moduli of dry rock and their applicationto predicting elastic velocities of sandstones.U.S.GeologicalSurvey Scientific Investigations Report 2005-5119,2005:1-14.
[31]Mindlin R D.Compliance of elastic bodies in contact.Journalof Applied Mechanics,1949,16:259-268.
[32]陈芳,周洋,苏新等.南海神狐海域含水合物层粒度变化及与水合物饱和度的关系.海洋地质与第四纪地质,2011,31(5):95-100.Chen F,Zhou Y,Su X,et al.Gas hydrate saturation and itsrelation with grain size of the hydrate-bearing sediments inthe Shenhu area of northern South China Sea.MarineGeology&Quaternary Geology(in Chinese),2011,31(5):95-100.
[33]Arp J J.The effect of temperature on the density andelectrical resistivity of sodium chloride solutions.Journal ofPetroleum Technology,1953,5(10):17-20.
[34]Guérin G,Goldberg D,Meltser A.Characterization of in situelastic properties of gas hydrate-bearing sediments on theBlake Ridge.J.Geophys.Res.,1999,104(B8):17781-17795.
[35]Wu N Y,Yang S X,Zhang H Q,et al.Gas hydrate systemof Shenhu area,northern South China Sea:Wire-linelogging,geochemistrical results and preliminary resourcesestimates.OCT,2010,20485,1-13.
[36]Hyndman R D,Spence G D.A seismic study of methanehydrate marine bottom simulating reflectors.J.Geophys.Res.,1992,97(B5):6683-6698.
[37]Minshull T A,Singh S C,Westbrook G K.Seismic velocitystructure at a gas hydrate reflector,offshore westernColombia,from full waveform inversion.J.Geophys.Res.,1994,99(B3):4715-4734.
[38]陆红锋,陈弘,陈芳等.南海神狐海域天然气水合物钻孔沉积物矿物学特征.南海地质研究,2009,20:28-37.Lu H F,Chen H,Chen F,et al.Mineralogy of thesediments from gas-hydrate drilling sites,Shenhu area,South China Sea.Geological Research of South China Sea(in Chinese),2009,20:28-37.
[39]Wang X J,Lee M,Wu S G,et al.Identification of gashydrate dissociation from wireline logs data in the Shenhuarea,South China Sea.Geophysics,2012,77(3):125-134.
[40]Heeschen K U,Tréhu A M,Collier R W,et al.Distributionand height of methane bubble plumes on the Cascadia margincharacterized by acoustic imaging.Geophys.Res.Lett.,2003,30(12):1643-1646.
[41]Gorman A R,Holbrook W S,Hornbach M J,et al.Migration of methane gas through the hydrate stability zonein a low-flux hydrate province.Geology,2002,30(4):327-330.
[42]龚建明,何玉华,闫贵京等.南海“神狐型”BSR特征及影响因素.石油实验地质,2011,33(6):602-606.Gong J M,He Y H,Yan G J,et al.Features and controllingfactors of BSR in Shenhu area,South China Sea.PetroleumGeology&Experiment(in Chinese),2011,33(6):602-606.
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