The Hunton Limestone in Oklahoma is an important reservoir in the oil and gas industry. Al-Shaieb et al. (1993) find that fractures in the Hunton Limestone are one of the key components of porosity with fracture permeability enhancing production. Fracture identification from surface seismic is an important topic, but little research in this area has been done on the Hunton Limestone. Hart (2006) has analyzed fractures using post stack seismic in the San Juan Basin, while Narhari et al. (2009) have analyzed fractures using post stack seismic data in Kuwait, both sandstones. Nissen et al. (2009) have used post stack seismic attributes to map fractures in the Arbuckle Limestone of Kansas, and calibrated their findings using a horizontal well adjacent to, but not in the seismic survey area. To our knowledge, little has been published on quantitative correlation of lineaments seen on post stack seismic attributes to fractures seen on horizontal wells. Therefore, this project is very important to developing an understanding of fracturing in limestones. From a preliminary 3D seismic attribute analysis of the area of interest, the attributes of curvature (positive and negative) and energy ratio have been the most helpful in predicting where a high density of fractures might exist and their general orientation. In addition to these attributes, approximately 10 miles of proprietary horizontal image logs have been obtained in the area of interest and will be studied to correlate fractures in the logs with proposed areas of fracturing in the seismic volume. This correlation should provide valuable information to locate and identify fracture patterns in the Hunton Limestone and enhance the ability to predict good areas of high porosity and permeability in both the Hunton and possibly other carbonates too. Fieldwork is being conducted in a specific test area in Oklahoma where an outcrop of the Hunton Limestone is exposed to characterize fractures in outcrop and create an analog for fracture patterns in the subsurface. Seismic data will be obtained in the outcrop area to further characterize the visible fractures with a seismic wavelet.
The Hunton Limestone or Hunton Group lies beneath the Woodford Shale which is separated from the Hunton by an unconformity. The Hunton Group is made up of shallow-marine carbonates deposited from the Late Ordovician to the Early Devonian and formed on a gently inclined ramp. Due to this depositional environment, the Hunton is laterally extensive in Oklahoma (Al-Shaieb et al., 1999).
The operator acquired a small 3D survey over the target area, which was processed through prestack time migration. The data quality at the Hunton horizon (Figure 1) is good, but suffers from acquisition footprint. Next we generated horizon slices through volumetric estimates of coherence and both long-wavelength and short-wavelength curvature (Figures 2a, 2b, 2c, and 2d). The long wavelength curvature attributes are typically indicative of larger bends and folds, while the short wavelength curvature attributes aide more in identification of smaller features, like possible fracture areas.
