基于海域地震资料的多次波及其鬼波的时距解释

doi:10.3969/j.issn.0253-4967.2020.01.015

摘要/Abstract

摘要：

当前陆域活动断层研究的相关理论方法已比较成熟, 但针对海域的活动断层探测和研究还很缺乏。由于海域中水表和海底等强反射面的存在, 多次波及其鬼波将对海域地震记录造成干扰, 有效模拟多次波及其鬼波是进行多次波识别和压制的前提。近海及构造复杂区往往存在倾斜界面, 基于水平界面假设的传统多次波压制方法难以准确地去除多次波的影响。文中结合海域地震记录及其采集方式, 基于倾斜界面多次波的时距解析, 针对近海等构造复杂区的实际记录利用简化模型预测多次波, 给出了来自不同界面(包括倾斜界面)的多次波及其鬼波的时距特征, 且与实际记录相吻合, 其结果可提高地震资料的观测解释能力; 在此基础上, 利用时距信息人工合成理论地震记录, 进行常规地震数据处理, 进一步认识不同界面的多次波时距、速度及其造成的层面假象等特征。本研究结果有利于有效识别和预测海域地震记录中的多次波, 为多次波的压制提供理论依据, 进而为海域地震活动构造探测研究提供一定的帮助。

关键词: 海域, 多次波, 鬼波, 时距模拟, 资料解释

Abstract:

Currently, the study on the active fault in the land areas is relatively mature, while there is still lack of detection and research on active faults in the sea areas. Marine exploration, which is different from land areas, has a prominent problem due to the existence of strong reflecting interfaces such as water surface and seafloor in the sea, thus the recording is often accompanied by interference of multiples on seafloor reflections. In addition, because of the characteristics of marine seismic exploration, the source exciting in the water and the geophone receiving in the water, ghost wave usually can be recorded simultaneously during the reflected wave propagation. This phenomenon makes it difficult to distinguish the effective waves and the noise, and has always plagued the data and seriously affects the quality of records. In the offshore and other regions of complex structures, such as inclined interfaces, it is difficult to eliminate the interference of multiples accurately by traditional multiples suppression methods, which are based on the horizontal interface assumption. This paper combines the sea area seismic data and its acquisition method, uses simplified model to simulate the multiples based on the time-distance analysis of multiples and their ghost wave in inclined interface. The time-distance characteristics of the multiples and their ghost waves from different interfaces(including the inclined interface)are obtained, and they are consistent with the actual records. The multiples time-distance simulation can help to distinguish the causes of reflected waves, summarize the multiple-wave time-distance characteristics from different interfaces(including inclined interfaces), and analyze the relationship between the characteristics of multiple waves and primary waves. In particular, this simulation has a significant effect on characterizing the internal multiples that are difficult to identify due to inconspicuous periodicity and the multiples of the inclined interface which present the phenomenon that the vertex of the time-distance curve is shifted. On this basis, relying on the time-distance analysis of ghost wave, we analyze the travel time difference characteristics between reflected waves and their accompanying ghost waves. The differences of the travel time characteristics of different orders ghost wave and reflected wave are summarized and the symmetry of the travel time difference between inclined interface and horizontal interface of ghost waves and reflected waves is analyzed. We simulate the distraction of the ghost wave event with the event of the reflected wave and analyze the influence of the ghost wave on the sea area seismic records. These results can improve the practical interpretation of seismic data. At last, the time-distance information is used to synthesize sea area seismic records, which can help us carry out the effective data processing and understand the characteristics of the time-distance and velocity of multiples in different interfaces and the layer artifact caused by multiples. This study combines the time-distance simulation of multiples and their ghost wave with conventional seismic data processing to analyze the pre-stack and post-stack features of multiple waves and their ghost waves in the seismic records of the sea area. The results of this study are conducive to the effective identification of multiples in seismic records in the sea, provide a theoretical basis for multi-wave suppression and prediction, and may facilitate the future study of sea-area seismic activity detection.

Key words: sea area, multiples, ghost waves, time-distance simulation, data interpretation

中图分类号:

P315.3⁺1

支明, 郝重涛, 姚陈, 于光明, 蔡明刚. 基于海域地震资料的多次波及其鬼波的时距解释[J]. 地震地质, 2020, 42(1): 226-244.

ZHI Ming, HAO Chong-tao, YAO Chen, YU Guang-ming, CAI Ming-gang. RESEARCH ON TIME-DISTANCE INTERPRETATION OF MULTIPLES AND GHOSTS BASED ON MARINE SEISMIC DATA[J]. SEISMOLOGY AND GEOLOGY, 2020, 42(1): 226-244.

图/表 13

图 1 多次波及鬼波反射路径示意图a 多次波反射路径; b 鬼波反射路径

Fig. 1 Reflection path of multiples and ghosts.

图 2 倾斜界面二次波及其伴随鬼波路径示意图a 单倾斜界面水表二次波路径; b 双倾斜界面震源鬼波+层间二次波+接收点鬼波路径

Fig. 2 Path of the secondary reflection and its ghost of inclined interface.

表1 实例一的模型地层参数

Table1 Model parameters of example 1

地层层序	地层法向深度 /m	地层倾角 /(°)(方向)	层速度 /m·s^-1
Ⅰ	3 350	0(水平)	1 500
Ⅱ	3 650	0(水平)	1 800
Ⅲ	4 550	8(上倾)	2 200

图 3 实例一的模型地层剖面

Fig. 3 Model stratigraphic section of example 1.

图 4 某实际深海海域地震资料与时距模拟结果的对比a 实际深海海域资料(刘衡, 2014); b 多次波的时距模拟结果

Fig. 4 Comparison between actual sea area seismic data and time-distance simulation result.

表2 实例二模型地层参数

Table2 Model parameters of example 2

地层层序	地层法向深度 /m	地层倾角 /(°)(方向)	层速度 /m·s^-1
Ⅰ	450	0(水平)	1 500
Ⅱ	1 050	0(水平)	1 700
Ⅲ	1 650	10(上倾)	2 000

图 5 实例二模型地层剖面

Fig. 5 Model stratigraphic section of the example 2.

图 6 浅水区地震资料与时距模拟结果的对比a 实际地震资料; b 多次波时距的模拟结果

Fig. 6 Comparison between epicontinental sea seismic data and time-distance simulation result.

图 7 实例二中层Ⅰ海底(水平界面)产生的伴随鬼波与反射波时差图a 震源鬼波+一次波与一次波的时差; b 一次波+接收点鬼波与一次波的时差; c 震源鬼波+一次波+接收点鬼波与一次波的时差;d 震源鬼波+二次波与二次波时差; e 二次波+接收点鬼波与二次波时差; f 震源鬼波+二次波+接收点鬼波与二次波的时差

Fig. 7 Time deviation between the ghost and reflected wave from sea floor in example 2.

图 8 实例二中层Ⅲ(倾斜界面)产生的伴随鬼波与反射波时差图a 震源鬼波+一次波与一次波的时差; b 一次波+接收点鬼波与一次波的时差; c 震源鬼波+一次波+接收点鬼波与一次波的时差;d 震源鬼波+二次波与二次波的时差; e 二次波+接收点鬼波与二次波时差; f 震源鬼波+二次波+接收点鬼波与二次波的时差

Fig. 8 Time deviation between the ghost and reflected wave from inclined interface in example 2.

图 9 正演模拟鬼波对地震记录的影响图中字母标示的反射波与其伴随鬼波类型与图6中的波型一致。 a 当震源深度为20m, 接收点深度为20m时的多次波及其鬼波的时距模拟及局部放大图; b 当震源深度为50m, 接收点深度为50m时的多次波及其鬼波的时距模拟及局部放大

Fig. 9 Forward modeling of influence of ghost waves on seismic data.

表3 人工合成记录观测系统参数

Table3 Observing system parameters of synthetic seismic data

炮数	炮间距/m	道数	道间距/m	震源深度/m	检波器深度/m	覆盖次数
200	10	1 000	10	7	9	500

图 10 人工合成记录速度谱与叠加剖面处理a 速度谱; b 动校正后的CDP; c 一次波叠加剖面; d混合的叠加剖面,P1、 Q1和R1为一次反射波形成的地层, 其余均为多次波反射形成的地层假象

Fig. 10 Velocity spectrum and stacked profile of synthetic seismic data.

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