东沙海域天然气水合物特征分析及饱和度估算

构造控制天然气水合物的赋存，在底辟构造、海底滑坡、活动断层和挤压脊等特殊地质体发育区是天然气水合物成藏的有利区域。不同地质体附近含水合物地层反射振幅强度和连续性各不相同，仅从地震剖面上难以进行准确识别。声波阻抗可以提供丰富的岩性信息。在东沙海域，以大洋钻探1148井的测井资料和叠加速度作为约束条件，采用约束稀疏脉冲反演方法，基于地震资料进行了波阻抗反演，获得了声波阻抗剖面，在声波阻抗剖面上水合物层表现为高声波阻抗异常，水合物层之下出现低声波阻抗异常。通过最小二乘法建立了1148井的声波阻抗与饱和水孔隙度之间的拟合关系式，计算出饱和水地层的孔隙度为40%~50%。基于阿尔奇方程，通过反演的声波阻抗计算了0101地震测线水域的水合物饱和度，其占孔隙空间的比例为10%~20%，含水合物地层呈横向部分连续分布特征。

Characteristic analysis and saturation estimation of gas hydrate in Dongsha sea area

The tectonic activity controls the occurrence of gas hydrate.Special structure bodies,such as diapir,submarine slide,active fault and compressive ridge are the favorable area of gas hydrate formation.The amplitude and continuity of reflections from gas hydrate neighboring different geologic bodies are different,which is difficult to be accurately recognized only from seismic profiles.Acoustic impedance can provide rock property information.In Dongsha sea area,taking the logging data and seismic stack velocity of ODP Leg at well 1148 as constraint,constrained sparse spike inversion was used to obtain acoustic impedance section.On the acoustic impedance section,the positive anomaly is shown in the gas hydrate-bearing zone and the negative anomaly is shown below the gas hydrate-bearing zone.The fitted formula between water-saturated porosity and acoustic impedance of well 1148 was derived by using lease square method.The calculated water-saturated porosity is 40%～50%.Based on Archie equation,gas hydrate saturation of line0101 was calculated by the inversed acoustic impedance,which is 10%～20% of the pore space.The gas hydrate-bearing formation appears to be layered and continuous.