含水合物松散沉积物声速剖面成像技术研究

摘要

According to the ultrasonic tomography technology based on ray theory, the adaptive noise cancellation was adopted to remove the premise of autoclave under the inherent noise. The straight ray-tracing method and the iterative algorithm based on SIRT algorithm were applied to realize forward modeling and inversion of the ultrasonic tomography. Then the acoustic velocity profile distribution images of hydrate formation in loose sediments were obtained. The results showed that the two-dimensional sound velocity profile structures of hydrate bearing sediments obtained by using ultrasonic tomography technology could accurately reflect the distribution of hydrate in sediments at different time and saturation. The P-wave velocity profile structures fit in well with S-wave velocity profile structures. Besides, with the experimental data, several velocity models were used to validate the relationship between the sonic velocity and the saturation of hydrate.%本文基于射线理论的超声层析成像技术,采用自适应消噪技术除去天然气水合物(NGH)实验模型固有噪声,运用直射线追踪法和基于联合迭代重建算法(Simultaneous Iterative Reconstruction Techniques, SIRT)的迭代重建法实现超声层析成像的正演和反演,针对水合物实验获取的波形,得到NGH在松散沉积物中形成时的地层声速剖面结构图像.结果表明,使用超声层析成像技术获取的含NGH沉积物的二维声速剖面结构能够准确反应不同时刻沉积物中 NGH 饱和度及分布情况,并且纵横波速度剖面结构的变化趋势大体相同.同时本文也结合常用的NGH声速预测模型,针对实验数据,对声速与NGH饱和度之间的关系进行了讨论.