南海北部神狐海域含天然气水合物沉积层的速度特征
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摘要
2007年在南海北部神狐海域对天然气水合物(以下简称水合物)的钻探结果表明,仅依靠似海底反射(BSR)和振幅空白不能揭示沉积层内水合物的赋存状态,不能准确地圈定水合物的分布面积和储层厚度。为准确判定水合物储层情况,对南海北部神狐海域声波测井及地震资料进行了精细分析,研究了含水合物沉积层的声波速度、地震速度的分布特征和变化规律。结果认为:①地震反射剖面上,由于水合物饱和度、厚度增大,引起含水合物沉积层的速度增大而产生上拉构造,其下方同时显示出因低速含气层引起的速度下拉构造,即"眼球状"的速度振幅异常结构;②含水合物层的层速度大小与沉积物孔隙度和水合物饱和度密切相关,水合物饱和度随声波速度升高而上下波动,总体趋势上随声波速度的升高而增高;③在含水合物带内部,高速层呈平行于海底的带状分布,底部速度最高,从底部往上速度逐渐降低;④利用上述特征,结合其他地质和地球物理资料,依据层速度可识别地层中水合物的存在,计算水合物的饱和度,确定含水合物层的厚度、分布范围,并可进一步计算水合物的资源量。
According to the drilling results of natural gas hydrate reservoirs in the Shenhu area,northern South China Sea,in 2007,both bottom simulating reflections(BSR) and blank reflections failed to reveal the storage of gas hydrate in sedimentary beds and were also incapable of accurately delineating the distribution area and reservoir thickness of gas hydrate.In view of this,we analyzed in detail the logging and seismic data from this study area,and studied the distribution characteristics and variations of sonic and seismic velocities in gas hydrate bearing formations.The following conclusions were obtained.(1) On the seismic reflection profile,the increases of gas hydrate saturation and reservoir thickness causes the increase of deposition rate of hydrate beds,thus a push-up structure is formed,below which a push-down structure occurs correspondingly due to the gas-bearing layers with a low deposition rate,which resulted in an augen-like amplitude anomaly.(2) The interval velocity of gas hydrate beds is closely related to the porosity and saturation of hydrate.The saturation of gas hydrate fluctuates with the increase of sonic velocity,but the overall trend is increasing with the increase of sonic velocity.(3) Within the gas hydrate bearing zone,the high velocity layers are featured by zonation distribution in parallel with the sea floor.The highest velocity occurs at the bottom of the gas hydrate bearing zone and the velocity decreases gradually upwards.(4) Based on the above characteristics,the interval velocity can be used to identify the existence of gas hydrate and to compute the saturation of gas hydrate.Combined with the other geological and geophysical data,the interval velocity can also be used to determine the thickness and distribution area of gas hydrate reservoirs,and to calculate the resource volume of natural gas hydrate.
According to the drilling results of natural gas hydrate reservoirs in the Shenhu area,northern South China Sea,in 2007,both bottom simulating reflections(BSR) and blank reflections failed to reveal the storage of gas hydrate in sedimentary beds and were also incapable of accurately delineating the distribution area and reservoir thickness of gas hydrate.In view of this,we analyzed in detail the logging and seismic data from this study area,and studied the distribution characteristics and variations of sonic and seismic velocities in gas hydrate bearing formations.The following conclusions were obtained.(1) On the seismic reflection profile,the increases of gas hydrate saturation and reservoir thickness causes the increase of deposition rate of hydrate beds,thus a push-up structure is formed,below which a push-down structure occurs correspondingly due to the gas-bearing layers with a low deposition rate,which resulted in an augen-like amplitude anomaly.(2) The interval velocity of gas hydrate beds is closely related to the porosity and saturation of hydrate.The saturation of gas hydrate fluctuates with the increase of sonic velocity,but the overall trend is increasing with the increase of sonic velocity.(3) Within the gas hydrate bearing zone,the high velocity layers are featured by zonation distribution in parallel with the sea floor.The highest velocity occurs at the bottom of the gas hydrate bearing zone and the velocity decreases gradually upwards.(4) Based on the above characteristics,the interval velocity can be used to identify the existence of gas hydrate and to compute the saturation of gas hydrate.Combined with the other geological and geophysical data,the interval velocity can also be used to determine the thickness and distribution area of gas hydrate reservoirs,and to calculate the resource volume of natural gas hydrate.
引文
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[2]王宏斌,梁劲,龚跃华,等.基于天然气水合物地震数据计算南海北部陆坡海底热流[J].现代地质,2005,19(1):67-73.WANG Hongbin,LIANG Jin,GONG Yuehua,et al.Esti-mation of the heat flow in the northern of the South ChinaSea based on the seismic data of gas hydrate[J].Geosci-ence,2005,19(1):67-73.
[3]梁劲,王宏斌,沙志彬.剩余层速度分析在南海天然气水合物解释中的指示意义[J].南海地质研究,2008:68-77.LIANG Jin,WANG Hongbin,SHA Zhibin.The significa-tion of remaining interval velocity analysis in interpretationof gas hydrates in South China Sea[J].Geological ResearchSouth China Sea,2008:68-77.
[4]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[J].现代地质,2008,22(3):447-451.LU Jing'an,YANG Shengxiong,WU Nengyou,et al.Welllogging evaluation of gas hydrates in Shenhu area,SouthChina Sea[J].Geoscience,2008,22(3):447-451.
[5]陆敬安,梁金强.分散型天然气水合物对储层的物性影响特征分析[J].南海地质研究,2008:54-57.LU Jing'an,LIANG Jinqiang.The impact analysis of dis-seminated gas hydrates on reservoir properties[J].Geolog-ical Research South of China Sea,2008:54-57.
[6]胡高伟,业渝光,张剑,等.沉积物中天然气水合物微观分布模式及其声学响应特征[J].天然气工业,2010,30(3):120-124.HU Gaowei,YE Yuguang,ZHANG Jian,et al.Micro-models of gas hydrate and their impact on the acousticproperties of the host sediments[J].Natural Gas Industry,2010,30(3):120-124.
[7]苏丕波,雷怀彦,梁金强,等.神狐海域气源特征及对天然气水合物成藏的指示意义[J].天然气工业,2010,30(10):103-108.SU Pibo,LEI Huaiyan,LIANG Jinqiang,et al.Character-istics of gas source in the waters of Shenhu and their signif-icance to gas hydrate accumulation[J].Natural Gas Indus-try,2010,30(10):103-108.
[8]王祝文,李周波,刘菁华.天然气水合物评价的测井响应特征[J].物探与化探,2003,27(1):13-17.WANG Zhuwen,LI Zhoubo,LIU Jinghua.Logging re-sponse characteristics in gas hydrates evaluation[J].Geo-physical&Geochemical Exploration,2003,27(1):13-17.
[9]甘华阳,王家生,陈建文,等.海底天然气水合物的饱和度预测技术[J].海相油气地质,2004,9(1):111-115.GAN Huayang,WANG Jiasheng,CHEN Jianwen,et al.Methods of predicting saturation of natural gas hydratewithin submarine sediments[J].Marine Origin PetroleumGeology,2004,9(1):111-115.
[10]王祝文,李周波,刘菁华.天然气水合物的测井识别和评价[J].海洋地质和第四纪地质,2003,23(2):97-102.WANG Zhuwen,LI Zhoubo,LIU Jinghua.Logging iden-tification and evaluation methods for gas hydrates[J].Ma-rine Geology&Quaternary Geology,2003,23(2):97-102.
[11]王秀娟,吴时国,郭旋,等.南海陆坡天然气水合物饱和度估计[J].海洋地质和第四纪地质,2005,25(3):89-95.WANG Xiujuan,WU Shiguo,GUO Xuan,et al.Estima-tion of gas hydrates saturation in the continental slope,South China Sea[J].Marine Geology&Quaternary Geol-ogy,2005,25(3):89-95.
[12]王秀娟,吴时国,刘学伟.天然气水合物和游离气估算的影响因素[J].地球物理学报,2006,49(2):505-511.WANG Xiujuan,WU Shiguo,LIU Xuewei.Factors af-fecting the estimation of gas hydrate and free gas satura-tion[J].Chinese Journal of Geophysics,2006,49(2):505-511.
[13]梁劲,王明君,王宏斌,等.南海神狐海域天然气水合物声波测井速度与饱和度关系分析[J].现代地质,2009,23(2):217-223.LIANG Jin,WANG Mingjun,WANG Hongbin,et al.Rela-tionship between the sonic logging velocity and saturation forgas hydrate in Shenhu area,northern slope of South China Sea[J].Geoscience,2009,23(2):217-223.
[14]梁劲,王宏斌,赵志超.射线追踪法在南海天然气水合物速度分析中的应用[J].物探化探计算技术,2007,29(6):486-491.LIANG Jin,WANG Hongbin,ZHAO Zhichao.The ap-plication of ray-tracing method in velocity analysis of gashydrate of the South China Sea[J].Computing Techniquesfor Geophysical and Geochemical Exploration,2007,29(6):486-491.
[15]刘学伟,李敏峰,张聿文,等.天然气水合物地震响应研究——中国南海HD152测线应用实例[J].现代地质,2005,19(1):33-38.LIU Xuewei,LI Minfeng,ZHANG Yuwen,et al.Studiesof seismic characteristics about gas hydrate:A case studyof line HD152in the South China Sea[J].Geoscience,2005,19(1):33-38.
[16]徐华宁,梁蓓雯,张光学,等.南海北部陆坡天然气水合物地震识别研究[J].天然气工业,2006,26(9):49-51.XU Huaning,LIANG Beiwen,ZHANG Guangxue,etal.Seismic identification of gas hydrates on Northern slopeof South China Sea[J].Natural Gas Industry,2006,26(9):49-51.
[17]SHIPEY T H,HOUSTON,BULLER R T,et al.Seis-mic evidence for wide-spread possible gas hydrates hori-zons on continental slopes and rises[J].AAPG Bulletin,1979,63(12):2204-2213.
[18]吴大奎,张本全,戴勇,等.地震资料气水识别方法及其应用[J].天然气工业,2011,31(12):54-58.WU Dakui,ZHANG Benquan,DAI Yong,et al.Seismic i-dentification methods for gas and water layers and their appli-cation[J].Natural Gas Industry,2011,31(12):54-58.
[19]ECKER C,DVORKIN J,NUR A.Sediments with gashydrates:Internal structure from seismic AVO[J].Geo-phys,1998,63(5):1659-1669.
[20]张聿文,刘学伟,金玉洁.含天然气水合物地层的速度和衰减研究[J].石油地球物理勘探,2004,39(2):205-214.ZHANG Yuwen,LIU Xuewei,JIN Yujie.Study of veloc-ity and attenuation for gas-bearing hydrate formation[J].Oil Geophysical Prospecting,2004,39(2):205-214.
[21]祝有海,赵省民,卢振权.中国冻土区天然气水合物的找矿选区及其资源潜力[J].天然气工业,2011,31(1):13-19.ZHU Youhai,ZHAO Shengmin,LU Zhenquan.Resourcepotential and reservoir distribution of natural gas hydratein permafrost areas of China[J].Natural Gas Industry,2011,31(1):13-19.
[22]傅宁,林青,刘英丽,等.白云凹陷天然气水合物气源条件再认识[J].中国石油勘探,2011,16(4):48-53.FU Ning,LIN Qing,LIU Yingli,et al.A rethinking up-on gas source condition of gas hydrate in Baiyun Sag[J].China Petroleum Exploration,2011,16(4):48-53.
[23]DVORKIN J,NUR A,YIN H.Effective properties of ce-mented granular material[J].Mechanics of Materials,1994,18(1):351-366.
[24]宋海斌.天然气水合物的地球物理研究[M].北京:海洋出版社,2003.SONG Haibin.Geophysical researches on gas hydrates[M].Beijing:Ocean Press,2003.
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