This paper investigates [Formula: see text]-anisotropy for characterizing fractured reservoirs — specifically, the variation of the seismic quality factor [Formula: see text] versus offset and azimuth (QVOA). We derive an analytical expression for P-wave attenuation in a transversely isotropic medium with horizontal symmetry axis (HTI) and provide a method (QVOA) for estimating fracture direction from azimuthally varying [Formula: see text] in PP-wave reflection data. The QVOA formula is similar to Rüger’s approximation for PP-wave reflection coefficients, the theoretical basis for amplitude variation with angle offset (AVOA) analysis. The technique for QVOA analysis is similar to azimuthal AVO analysis. We introduce two new seismic attributes: [Formula: see text] versus offset (QVO) gradient and intercept. QVO gradient inversion not only indicates fracture orientation but also characterizes [Formula: see text]-anisotropy. We relate the [Formula: see text]-anisotropy parameter [Formula: see text] to fractured-medium parameters and invert the QVO gradient to estimate [Formula: see text]. The attenuation parameter [Formula: see text] and Thomsen-style anisotropy parameter [Formula: see text] are found to be interdependent. The attenuation anisotropy magnitude strongly depends on the host rock’s [Formula: see text] parameter, whereas the dependence on fracture parameters is weak. This complicates the QVO gradient inversion for the fracture parameters. This result is independent of the attenuation mechanism. To illustrate the QVOA method in synthetic data, we use Hudson’s first-order effective-medium model of a dissipative fractured reservoir with fluid flow between aligned cracks and random pores as a possible mechanism for P-wave attenuation.

Se tomaron en consideración distintos aspectos de algunas técnicas computacionales para el análisis AVOA (Amplitud Versus Offset y Azimut), para la composición de fracturas, en particular: utilizando amplitudes en lugar de coeficientes de refección, suavizando los datos sísmicos y el método de la estimación numérica para calcular la dirección. Se estimó un nuevo método de cálculo y se indica un nuevo método suavizado. Se compararan distintos métodos de cálculo en los datos sintéticos de superficie de reflección, con y sin ruido. Se obtuvieron propiedades de los métodos numéricos, dependientes de conjuntos distintos de los azimut y los offset. Se muestra una superioridad del nuevo método.Palabras clave: AVOA, medio HTI, anisotropía sísmica, caracterización de yacimientos fracturados.

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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.

Se desarrollan nuevas técnicas de cálculo en el análisis del factor de calidad frente a la distancia fuente receptor y el acimut (QVOA) para caracterización de fracturas. Estas técnicas se aplican a datos sintéticos superficiales de reflexión con ruido.Palabras clave: QVOA, factor de calidad, medio HTI, anisotropía sísmica, caracterización de yacimientos fracturados.