The Eagle Ford Shale is an emerging shale gas play in South Texas. Seismic data from the area are dominated by high amplitude reflections from carbonates and salt. The combination of land acquisition and processing challenges can produce noisy 3D seismic data volumes that are difficult to interpret. Structurally oriented noise reduction techniques remove noise while preserving signal, creating a volume that is easier to interpret. Seismic attributes calculated on the cleaner data provide a better picture of the subtle stratigraphy in this area.
The Eagle Ford Shale is a marine shale located in South Texas that was deposited during the Upper Cretaecous. It is an emerging unconventional play, with fewer than 100 wells drilled so far. It has recently attracted the attention of major oil companies and is proving to be competitive with the Haynesville and Marcellus due to higher liquid content and lower well costs. Additionally, the Eagle Ford has a higher carbonate to shale percentage, making it brittle and thus more “fracable” and is not as highly pressured as the Haynesville. While it is primarily a gas play, some oil has been discovered in the southwest portion of the trend. Geophysical support for the play will become more critical as many companies receive 3D data sets in the area in 2010. The depth, thickness, and mineralogy of the shale can vary significantly over short distances and at different scales (Liro et al., 1994). Seismic attributes can be a critical factor in identifying these changes. Sandwiched between the Austin Chalk and the Edwards, the Eagle Ford can be overwhelmed by these bright reflectors. We can utilize seismic attributes as we move from understanding the Eagle Ford as a source rock into a reservoir context. Live Oak County, Texas, is the site of several recent discovery wells in the Eagle Ford, with many more wells planned for 2010. We present examples of seismic data conditioning and attribute analysis on a 3D seismic volume from Sinor Ranch in Live Oak County to help increase our understanding of the geologic context of the play.
After the rifting that occurred during the Jurassic, the Cretaceous period was relatively quiescent in the northern Gulf of Mexico. In the early Cretaceous, shelf-edge reefs developed along the boundary between the continental shelf and Gulf of Mexico basin. In the late Cretaceous, no reefs formed; the Eagle Ford was deposited during a transgression that covered the reefs with lime mud and shale (Condon and Dyman, 2006). The Eagle Ford consists of a lower transgressive unit of dark shales and an upper highstand of unit shales and limestones. The lower unit was deposited in a lower energy, poorly oxygenated environment and is more oilprone. The upper unit accumulated in a higher energy, shallower water environment during a regressive highstand and is gas-prone (Dawson, 2000; Liro et al., 1994). There is a regionally recognizable unconformity at the base of the Eagle Ford, and the Austin Chalk lies unconformably on top of the Eagle Ford.
