【作者】 王秀娟；

【导师】 吴时国；

【作者基本信息】 中国科学院研究生院（海洋研究所） ， 海洋地质， 2006， 博士

【摘要】 本文对南海北部天然气水合物的成矿条件进行了研究,结果表明水合物存在于滨海-浅海-半深海-深海的沉积环境中,其中等深流、三角洲、浊积扇、滑塌沉积、底辟等沉积体系有利于水合物形成,尤其是沉积速率高、构造复杂、流体活跃、含砂率适中(35%～50%)、细粉沙粘土或细粒沉积物中,更有利于水合物成藏。南海北部的台西南盆地、东沙群岛海域、西沙海槽、琼东南盆地是天然气水合物远景区,其中台西南盆地为最有利区。含水合物沉积层具有高P-波速度、高弹性阻抗、高P-阻抗、高S-阻抗、高λρ、略微低泊松比,而含游离气沉积层具有低P-波速度、低弹性阻抗、低P-阻抗、正常的S-阻抗、低λρ和低泊松比等。研究沉积层弹性性质,对水合物研究具有重要意义。从测井和地球化学研究看,含水合物沉积层具有高电阻率异常、低氯离子浓度异常、高氧同位素异常等。针对南海北部台西南盆地和东沙海域的三条测线进行了约束稀疏脉冲反演,从声波阻抗剖面看,台西南盆地较东沙海域更利于形成水合物。台西南盆地地区构造复杂、断层发育、存在底辟构造,为深层流体(水和气体)和热聚集提供良好的通道;而从东沙群岛西部的珠江口盆地的沉积环境相对比较稳定,位于隆起和坳陷分界处规模较大的活动断层相对比较少,缺乏气体运移通道。分别基于迭代正演模拟反演法和阿奇方程从声波阻抗估算无井和有井地区饱和度,该方法给出了从地震反演的声波阻抗估算天然气水合物和游离气饱和度。从南海北部水合物和游离气饱和度估算结果看,台西南盆地水合物饱和度呈片状和块状分布,横向分布不连续,水合物饱和度占孔隙空间的10-30%,最高值达50%;深部含有少量游离气,呈不连续的层状分布,饱和度占孔隙空间的2-3%,局部层位饱和度比较高,达到6-7%且BSR比较清晰。东沙群岛BSR相对较弱;水合物呈层状分布,横向变化不大,饱和度占孔隙空间的10-20%,局部较高。更多还原

【Abstract】 The mineral formation conditions of gas hydrate-bearing sediments in the northernSouth China Sea are studied in the dissertation. The research result shows that gas hydrateis likely to locate in the offshore, continental shelf, bathyal and abyssal depositional setting,especially in contour flow, delta, turbidite fans, slump deposit, diapir depositional system.In area, there are high sedimentation rate, complex geology, active faults, moderate sandyrate (35-50%), fine sandy clay and fine grained sediment, which are favor of the formationof gas hydrate. Prospective areas of gas hydrate in the northern South China Sea aredelineated, such as Taixinan basin, Dongsha Islands, Xisha trough and Qiongdongnan basinand so on, especially in Taixinan basin.By analyzing the elastic properties of gas hydrate-bearing sediments, the hydratedsediments have high compressional-wave velocity, high elastic impedance, highP-impedance, high S-impedance, high λρ and slightly lower Poisson’s ratio. Freegas-bearing sediments have low compressional-wave velocity, low elastic impedance, lowP-impedance, non-anomalous background S-impedance, low λρ and low Poisson’s ratio.Moreover, gas hydrate-bearing sediments have relatively high resistivities, low chlorideand high Oxygen Isotopic anomaly. Constrained Sparse Spike Inversion is used to obtainacoustic impedance profile in Taixinan basin and Dongsha Islands. Complex structuralsetting, well-developed fault systems and complex diapiric structures in Taixinan basinsupply good pathway for the migration of gas from deep to shallow sediments.Depositional setting of Pearl River Mouth basin in the west of Dongsha Islands is relativelystable and large scale faults are few between uplift and depression.Acoustic impedances based on iterative forward simulation inversion and Archie’sequations are used to estimate saturations in the area with well log and without well logdata. The methods are applied to multiple channel seismic data and well logs from thenorthern of South China Sea. Gas hydrate distribution nearby Taixinan Basin is patchy,noncontinuous and saturation is about 10-30% of the pore space, with the highest values of50%. Free gas is present in this zone with about 2-3% of the pore space. BSR is strongerthan that without free gas below GHSZ. The BSR is weak in Dongsha Islands. Gas hydratedistribution is layered, continuous and the saturation is about 10-20% of the pore space,while local zone is high.更多还原