Seismic Attribute Construction of Fault Scale Indicator Based on Coherence Versus Frequency

Fault prediction is an important research domain in seismic exploration. However, most of the methods are qualitative analysis, and the quantitative detection of fault needs to be further studied for comprehensive oil and gas reservoir exploration and development. In this paper, a novel fault quantitative characterization method named fault scale indicator (FSI) based on coherence versus frequency (CVF) is proposed, this new attribute is well defined and calculated to realize the quantitative analysis of fault characterization. Firstly, we analyze the features of frequency-dependent coherency attribute theoretically of faults with different scales. According to the idea of AVO attribute, we define the fault scale indicator (FSI) based on coherence versus frequency (CVF), and establish the relationship between FSI attribute and fault scale. Taking the cross-correlation for example, we define the formula of coherence calculation. Based on the above coherence calculation formula, we define the fault scale indicator (FSI) by conducting derivation for coherence with respect to the parameter of frequency, so we obtain the FSI attribute for quantitative fault characterization. Then through seismic forward modelling and analysis of fault model with different scales, the rationality and reliability of fault scale indicator is verified. The large scale fault (50 m × 10 m) has the smallest FSI attribute and the small scale fault (10 m × 2 m) has the largest FSI attribute. FSI can well describe the fault quantitative features than other qualitative methods. Finally, we carry out fault description in practical work area in Shunbei oil and gas field of fault-controlled fracture-cavity reservoir in Tarim Basin, China. Results shows that FSI attribute can improve the quantitative characterization accuracy of fault detection greatly, which is helpful for fault-controlled reservoir prediction and well target design. In addition, the drilling fluid leakage is usually regarded as the indicator of developed reservoir. We establish the relationship between FSI value and drilling fluid leakage, which verifying the reliability of this FSI attribute. So the spatial varying of FSI value is also beneficial to the connectivity feature analysis of the fault-controlled reservoir. FSI attribute provides a new way for comprehensive fault analysis.