【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。更多还原

【Abstract】 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.更多还原