沿层谱比的物理意义及实用价值

The geophysical meanings of horizon-based spectrum ratio and its practical values

1. 成都理工学院,四川成都610059;2. 石油地球物理勘探局,河北涿州072751

1. Chengdu University of Technology, Chengdu 610059, China;2. Bureau of Geophysical Prospecting for Petroleum, Zhuozhou072750, China

地面所记录的来自地下某一目的层的反射波,主要是激发子波、目的层及大地滤波改造后的信号 (忽略干扰影响)。在这样的地面记录中,子波及大地滤波的影响占据主导地位,目的层岩性及物性的变化引起的异常在记录中是很弱的,一般情况下这些异常无法提取或识别,要想直接消除激发子波及大地的影响也同样不可能。在一定条件下,如果采用沿层短时窗谱比,则能突出目的层由于岩性或物性变化引起的地震响应,进而较好地检测目的层的岩性或物性变化,达到油气 (特别是含油)预测的目的。以薄层 (而不是界面)反射为基本的反射单元,从理论入手,找出了薄层反射波的地面记录横向谱比的物理意义。

The reflection waves recorded at the earth surface consist mainly of shooting wavelet and signals reformed by reflectors and formations if noises are ignored. For such records, the influences from the wavelet and the filtering of the earth prevails over the responses caused by variations in lithology and petrophysics. Therefore, it is hard to extract the responses from the records, and it is also impossible to remove the influences from the wavelet and the earth directly. However, under certain conditions, seismic responses caused by variations in lithology and petrophysics can be highlighted by horizon-based spectrum ratio in short time windows. Furthermore, with the more accurate variations in lithology and petrophysics of the targets, hydrocarbon accumulation can be inferred. In the paper, the author deduced the geophysical meanings of horizon-based spectrum ratio of surface records from thin reflectors. Model experiments show that the method is feasible in predicting lateral velocity variations of thin interbedding reservoirs.