Summary
Coherency attribute can be used to detect anomalous structures, such as faults and channels, which are closely related to the distribution and migration of oil and gas. In this paper, we propose a multitrace complex-valued correlation method including both inline and crossline directions for detecting edges more accurate. A 3-D model data is used to test the performance of the proposed method. Results show that the multitrace complex-valued correlation can highlight edges of faults and channels, which can not be detected efficiently by correlation between two neighbouring traces. When applied to a 3-D real seismic data, this method identifies large and small faults simultaneously, and the existence of these faults is confirmed by manual interpretation on seismic sections.
Introduction
Detecting anomalous structure in the subsurface is a key goal of seismic exploration because of the close relationship between anomalous structure and distribution of oil and gas. In order to extract discontinuous seismic response caused by variation in structure, lithology, stratigraphy and so on, the coherency technique is proposed to detect discontinuities such as faults and channels. Bahorich and Farmer (1995) presented the C1 coherency algorithm that estimates discontinuity in stratum and lithology by calculating cross-correlation coefficient of neighbouring seismic traces. Marfurt et al. (1998) applied coherency analysis to arbitrarily multitrace of seismic data and obtained statistics multitrace coherency information in analysis window, which was defined as the C2 coherency algorithm. Based on the eigenstructure of covariance matrix formed from the seismic traces, Gersztenkorn and Marfurt (1999) proposed the C3 coherency algorithm which is also a multitrace coherence measure. In recent years, several methods such as higher-order statistic have been improved from C1 to C3 coherency algorithm to detect discontinuous seismic signal.
Compared with conventional coherency algorithm, complex-valued correlation is not only computationally inexpensive, but can produce both dip related information and coherency measurements. Taner et al. (1979) firstly showed complex-valued cross-correlation of two analytic traces and mainly focused on its amplitude in connection with the power ratio and semblance. O’Doherty and Taner (1992) calculated instantaneous frequency and dip by utilizing phase shift of complex-valued autocorrelation at zero-lag. Complex trace was used in semblance calculation (Marfurt, 2006) to estimate dip and azimuth in 3-D seismic data, and the concept of complex-valued covariance was mentioned as well. Browaeys (2009, 2010) presented a local complex correlation which can compute local coherency coefficient and phase shift between two neighbouring seismic traces.
