ASSESSMENT OF CARBONATE FORMATIONS IN THE APPALACHIAN BASIN

An assessment of the major carbonate units in a portion of the Appalachian basin has been performed to gauge their suitability in the development of new natural gas storage capacity using fracturing followed by matrix dissolution with acid. The goal of the project is to identify major carbonate units that would be suitable for creating cavern storage with this new method.

The evaluation of carbonate units covers all major formations in the Appalachian basin from the Cambrian to the Mississippian. In this phase of the project the regional trend of the formations was considered to be more important than the local variability. In most cases, the wells used to make the maps were selected on three criteria: depth, location, and availability of formation tops picked by geologists. Data from the selected wells were obtained from state geological surveys in New York, Pennsylvania, West Virginia, Ohio, Kentucky, and Indiana. The databases were filtered manually and digitally, and then converted to a GIS format. Products created include structure contour maps, carbonate-interval isopach maps, and depth to top carbonate maps. The latter type of map was created because the depth to the top of each carbonate interval is one of the suitability criteria for developing the new gas-storage technology. The depth map was constructed by subtracting the top carbonate elevation surfaces from a digital elevation surface map of each state using map algebra techniques and was smoothed with neighborhood statistical methods, assuring that the well data were honored in the final map.

In addition to the map-making capabilities of GIS, other advanced spatial analysis techniques can be used to examine regional geologic trends and to determine the suitability of each unit for applying the new fracture-dissolution method. Other data types that can be correlated with the carbonate formation maps are stratigraphic information, locations of existing gas-storage fields, pipelines, railroads, navigable waterways, and population centers. Analysis of the maps produced is providing information useful to fossil-fuel exploration, new insight into the structural configuration of the Appalachian basin, and results for assessment of suitability for developing the new method of creating natural gas storage.