QVOA analysis as an instrument for fracture characterization

Abstract

We present a method for estimation of preferred P-wave attenuation direction in fractured media based on azimuthally varying attenuation. The method can be applied to Q-estimates extracted from multi-azimuthal 3D seismic data involving surface reflection data and VSP. The method proposed is called QVOA analysis (that means variation of attenuation, or seismic quality factor Q, versus offset and azimuth); it is based on an analytical expression for P-wave attenuation as a function of wavepropagation direction in HTI medium. The expression appears to be similar to Rüger's approximation for PPwave reflection coefficient as a function of incidence angle and source-receiver-line azimuth. In this connection, the proposed technique of QVOA analysis is similar to the well-developed technique for azimuthal AVO analysis (AVOA). An application of the method is illustrated on synthetic data generated from Hudson's effective-medium model with a fluid-flow attenuation mechanism. Also we predict relationships between attenuation anisotropy and fractured medium properties.

QVOA Techniques for Estimation of Fracture Directions

“…As shown in Figure 2, the dependence of on sin 2 can differ from the quadratic dependence prescribed by (6). There are two ways to take this discrepancy into account.…”

“…There are two ways to take this discrepancy into account. The first is to formally add a term (6). This leads to solving a nonlinear system of 11 equations in the leastsquares method.…”

“…In this context, the interest is considering for oil layers the function of quality factor , which characterizes the magnitude of this viscous attenuation. The equation for dependence of factor on the direction of fractures was proposed by Chichinina et al in works [6,7] and serves as the basis for QVOA techniques (Quality factor Versus Offset and Azimuth).…”

Experimental study on the effect of fracture scale on seismic wave characteristics

“…Zhu (2004; studied the attenuation in the fractured model by using the Thomsen theory. Chichinina (2004;2005) proposed a theory called "QVOA" (seismic quality factor Q versus offset and azimuth) to study the characteristics of the fractured media, and gave the relationships among the parameters of the anisotropy. Chapman (2003) and Liu (2006) did some research on kinematic and dynamic anisotropy.…”

Intrinsic and apparent seismic attenuation in VSP data

“…At the 75 th Annual SEG Meeting several authors (e.g. Chichinina et al, 2005;Gray, 2005;Maultzsch, 2005) presented their investigations of Q-anisotropy. Could some of this observed offset dependence be explained by Q-anisotropy?…”