Buda-Georgetown Lime Play
The Buda-Georgetown Lime play has seen a resurrection of interest in the last couple of years, thanks in part to the different types of sub-plays within the two Cretaceous formations. The Buda is a biomicritic limestone lying below the Eagle Ford Shale, in most areas of Texas. The Georgetown is below the Buda, separated by a thin shale formation known as the Del Rio Shale. Typically, the Georgetown is also a biomicrite; but, there are exceptions to this generalization, making the play more interesting and challenging for oil and gas companies.
Statistically speaking, the Buda and Georgetown zones under-perform the Austin Chalk's productivity. This has often been attributed to the fact that these two zones usually exhibit lower primary matrix porosity, and are believed to have large open fractures that deplete quickly, without the support of matrix or micro-fractures. Another problem has been the assumption that a good Austin Chalk area should be a good Buda-Georgetown area, but this is certainly not the case. In fact, good Buda and Georgetown producing areas are often up-dip of the main Austin Chalk trend.
A new development in the trend has been in the pursuit of Georgetown that has significant primary matrix porosity. The normal matrix porosity in the Buda and Georgetown is 3 to 4 percent, but some areas of Georgetown may have 8 to 10 percent matrix porosity. These areas are producing some tremendous wells, with some wells yielding as much as 50 million cubic feet of gas per day (MMCFGPD). Depths vary from 4,000’ to 14,000’. The higher matrix porosities support the idea that Georgetown wells can make good candidates for hydraulic fracture treatments. Figure 1 shows some of the recent “hot-spots” of activity.
Mapping the fairway of the trend is not difficult, and requires no seismic. Good mapping begins with production EURs (Estimated Ultimate Recoveries) tied to simple log parameters. Relative performance can be predicted with good mapping, and it is important to note that areas with 30,000 to 100,000 barrel oil cum wells would have been considered uneconomic, but with modern commodity prices, they become areas to target.
To summarize, the key features to keep in mind about this play are:
- New areas are being developed, with high Initial Potentials (IPs).
- One key to better wells is recognizing areas with some matrix porosity.
- The economic hurdles have been lowered with new commodity prices.
- The two geological formations are easy to drill together and produce with one surface well having two laterals.
- Some wells show a good response to hydraulic fracture stimulations.