Azimuthal variations in attributes for induced fracture detection in the Barnett Shale

Abstract

Wide azimuth seismic data acquisition has become standard in many plays where azimuthal characterization of fractures or stress is important for fully understanding reservoir behavior. Usually, the desire is to image preexisting fracture networks, but, in artificially stimulated reservoirs, it is also desirable to understand the fracture state after completion. To characterize the induced fractures in a heavily drilled area of the Barnett Shale, a wide azimuth survey was acquired and processed to generate four separate azimuthal stacks. Attributes exploiting variations in amplitude and waveform were independently calculated for each azimuthal stack. Azimuthal variations in the attributes were then quantified through ellipse fitting. The attributes with the most statistical significance in azimuthal variability were those related to frequency such as the wavelet dominant frequency. These attributes were consistent with each other but show a wide distribution over azimuths across the survey. In addition, random distribution of orientations within the Barnett shale compared to the over and underlying Marble Falls and Viola Limestones indicate a difference in orientation for the induced as opposed to preexisting fractures. With the ability to map the induced fractures, it becomes feasible to take an intelligent approach to planning infill locations to avoid the previously fractured areas.

Vector correlation of amplitude variation with azimuth and curvature in a post-hydraulic-fracture Barnett Shale survey

“…Note that mostpositive curvature ridges appear to form boundaries to production for surveys A and B. This observation is consistent with that of Trumbo and Rich (2013), who use microseismic data to show that such ridges form fracture barriers. Figure 17a and 17b shows microseismic events, horizontal well paths plotted on top of phantom Figure 17.…”

“…Survey B was acquired before hydraulic fracturing, and it is discussed by Aktepe et al (2007) and Perez and Marfurt (2014). Survey A was acquired after hydraulic fracturing with approximately 308 vertical or directional wells and 127 horizontal wells and is discussed by Zhang et al (2013), Trumbo and Rich (2013), and Perez and Marfurt (2014). Figure 8a shows a time structure map of the Viola Limestone whereas Figure 8b shows a representative vertical slice AA′ through the data.…”

Seismic attributes and the road ahead

“…This suggests that prestack spectral analysis (frequency vs. angle) can be a measure of rugosity. Trumbo and Rich (2013) found that frequency vs. azimuth is a simple but accurate measure of azimuthal anisotropy. In her distinguished lecture Lynn (2004) hypothesized that one can estimate open fractures by measuring Q (1/attenuation) as a function of azimuth.…”