东海天然气水合物地球物理特征及全波形反演方法研究

IOCAS-IR > 海洋环流与波动重点实验室

	东海天然气水合物地球物理特征及全波形反演方法研究
其他题名	SEISMIC CHARACTERISTICS OF GAS HYDRATES IN EAST CHINA SEA AND STUDY OF FULL WAVEFORM INVERSION
	徐宁
学位类型	博士
	2007-06-06
学位授予单位	中国科学院海洋研究所
学位授予地点	海洋研究所
关键词	天然气水合物泥底辟地震属性叠前全波形反演冲绳海槽
摘要	地球物理方法是目前海域天然气水合物和游离气识别与预测分析的重要手段，并且已经由早期主要研究地层的速度和振幅信息发展到利用波形特征进行叠前反演，提取多种属性、多种弹性参数进行综合分析的阶段，因此对水合物地层进行综合地球物理属性研究具有重要的理论意义和实践意义。本文通过对2001年东海973航次在冲绳海槽取得的多道地震数据进行有针对性的特殊处理，并通过精细地地震地层解释，发现海槽南部存在大量的泥底辟构造并伴生天然气水合物。针对DMS01-5测线上的泥底辟构造，分别从叠加速度分析、砂泥岩比分析、计算海底热流与实测海底热流对比分析、流体势能分析和波阻抗反演分析等几方面探讨了泥底辟型天然气水合物的地球物理特征，并对该处底辟顶部和其周围岩层中似海底反射（BSR）的成因进行了探讨，认为这里的BSR并不代表天然气水合物稳定带的底界，而分别对应于天然气水合物生成带的底界和游离气的顶界。基于波动方程的一维半空间叠前全波形反演可以求取多个弹性参数，同时可以获得水合物沉积层精细的速度结构，这对天然气水合物和游离气的识别进而估算天然气水合物和游离气的含量至关重要。本文系统讨论了在Kennett广义反射透射系数矩阵正演基础上叠前全波形反演的遗传算法。Kennett广义反射透射系数矩阵正演算法包含了自由表面反射、薄互层层间多次反射波、透射反射波以及P-SV波之间的相互转换波，适合水合物层精细速度结构研究。采用遗传算法进行全波形反演克服了传统局部线性最优化方法依赖初始模型，需要利用目标函数导数信息的不足之处，算法收敛速度较快并且具有一定的稳定性。
其他摘要	The most gas hydrates and free gases in the marine strata were identified and predicted by using the seismic data for quantitative analysis over the past decades. Most of these quantitative studies relied on the P wave seismic velocities and the seismic reflection amplitude variation associated with the presence of the gas hydrates and free gases. Additional information was contained in the detailed waveforms. As a result, multi-attribute analysis of prestack seismic data for identification of gas hydrates was developed. Many mud diapirs had been recognized in southern Okinawa Trough by a multi-channel seismic 973 surveying on R/V KEXUE I in 2001. Gas hydrates had been found in the layers immediately above mud diapirs and in the host sediment. Formation of mud diapirs on the seismic line DMS01-5 and their seismic characteristics associated with gas hydrates were studied via stacking velocity analysis, heat flow calculation from the bottom simulating reflector (BSR), fluid potential analysis, density and interval velocity measurements, and impedance inversion. It has been found that the BSRs are not always be indicative of the base of the gas hydrate stability zone (BGHSZ), which could indicate the base of the saturated gas hydrate formation zone (BSGHFZ) and the top of the free-gas zone (TFGZ) in different mud-diapir-associated strata. In this thesis a prestack full waveform inversion using a genetic algorithm was presented to obtain the P and S wave seismic velocities of a horizontally, finely layered elastic medium. The generalized reflection transmission matrix method intruded by Kennett was chosen to calculate a complete seismic response for a stratified elastic half space, which including free-surface waves, mode conversions and multiple reflections. Genetic algorithm was a global optimization algorithm, which worked with a group of models simultaneously and used stochastic processes to guide the search for an optimal solution with little priori constrains, other than the conventional local linearization algorithms which required a good starting model and the derivative information.
页数	128
语种	中文
文献类型	学位论文
条目标识符	http://ir.qdio.ac.cn/handle/337002/1299
专题	海洋环流与波动重点实验室
推荐引用方式 GB/T 7714	徐宁. 东海天然气水合物地球物理特征及全波形反演方法研究[D]. 海洋研究所. 中国科学院海洋研究所,2007.

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