Fracture detection in a carbonate reservoir using a variety of seismic methods

Abstract

We combine various methods to estimate fracture orientation in a carbonate reservoir located in southwest Venezuela. The methods we apply include the 2-D rotation analysis of 2-D P-S data along three different azimuths, amplitude‐variation‐with‐offset (AVO) of 2-D P-wave data along the same three azimuths, normal‐moveout (NMO) analysis of the same 2-D data, and both 3-D azimuthal AVO and NMO analysis of 3-D P-wave data recorded in the same field. The results of all methods are compared against measures of fracture orientation obtained from Formation microScanner logs recorded at four different locations in the field, regional and local measures of maximum horizontal stress, and the alignment of the major faults that cross the field. P-S data yield fracture orientations that follow the regional trend of the maximum horizontal stress, and are consistent with fracture orientations measured in the wells around the carbonate reservoir. Azimuthal AVO analysis yields a similar regional trend as that obtained from the P-S data, but the resolution is lower. Local variations in fracture orientation derived from 3-D AVO show good correlation with local structural changes. In contrast, due to the influence of a variety of factors, including azimuthal anisotropy and lateral heterogeneity in the overburden, azimuthal NMO analysis over the 3-D P-wave data yields different orientations compared to those obtained by other methods. It is too early to say which particular method is more appropriate and reliable for fracture characterization. The answer will depend on factors that range from local geological conditions to additional costs for acquiring new information.

Multi-Attribute Seismic/Rock Physics Approach to Characterizing Fractured Reservoirs

“…In most cases, seismic field studies for fracture detection are designed to find nearvertical and open joints (Teng, 1998;Grimm, 1999;Perez, 1999;. However, in the proximity of the faults, sometimes the host rock can be very fractured, giving rise to the so-called "breccia zone".…”

“…Most of the seismic field studies for fracture detection have as targets, vertical and open joints Lynn, 1997, Teng, 1998;Grimm et al, 1999;Perez et al, 1999;Lynn et al, 1999). A single set of vertical, parallel fractures embedded in an isotropic background can be described using a transversely isotropic model with a horizontal axis of symmetry (HTI).…”

Characterization of in-Situ Stress and Permeability in Fractured Reservoirs

“…Amplitude variation with offset and azimuth (AVOA) has been widely used to identify the orientation of vertical fractures with variable levels of success (Ruger, 1998;Mallick et al, 1998;Perez et al, 1999;Shen and Toksoz, 2000;Minsley et al, 2003). In these applications, the fractures are assumed to be small relative to the wavelength of the seismic waves.…”

“…Much effort has focused on measuring amplitude variations with offset (AVO) for seismic reflections from a fractured reservoir (Gray et al, 2002, Perez et al, 1999, and Shen et al, 2002. Amplitude variation with offset and azimuth (AVOA) has been widely used to identify the orientation of vertical fractures with variable levels of success (Ruger, 1998;Mallick et al, 1998;Perez et al, 1999;Shen and Toksoz, 2000;Minsley et al, 2003).…”

Characterization of in-Situ Stress and Permeability in Fractured Reservoirs

“…In the characterization of fractured reservoirs, nowadays mature techniques include the processing of converted waves, AVOA analyses of P wave, NMO ellipticity, and others (Pérez et al, 1999). In all these techniques, the effect of fractures in the wave propagation is described by an equivalent azimuthally anisotropic medium.…”