Possible Continuous-Type (Unconventional) Gas Accumulation in Lower Silurian "Clinton" Sands, Medina Group, and the Tuscarora Sandstone in the Appalachian Basin: A Progress Report of 1995 project activities

Robert T. Ryder, Kerry L. Aggen, Robert D. Hettinger, Ben E. Law, John J. Miller, Vito F. Nuccio, William J. Perry, Jr., Stephen E. Prensky, John R. SanFilipo, and Craig J. Wandrey

Open-File Report 96-42

GAS PRODUCTION AND DECLINE OF SELECTED WELLS

Estimated ultimate recoverable (EUR) gas from individual wells is an essential parameter for assessing recoverable gas in continuous-type (unconventional) accumulations in reservoirs such as the "Clinton" sands and Medina Group sandstones (Schmoker, 1995b). Basically, the EUR probability distribution for a set of producing wells in a given play can be used to approximate an expected EUR distribution for wells in undrilled parts of the play. EUR's either may be calculated directly from production-history records of abandoned wells or calculated from production decline curves of active or shut-in wells. As a rule, wells must have produced gas from the same reservoir for at least 5 years to provide a reliable decline curve. In the Appalachian basin, oil and gas production data for fields and wells have been compiled by most State Oil and Gas Agencies and State Geological Surveys since the early 1960's and many of them are available in digital form. Proprietary production files and data bases have been compiled by several oil and gas companies and consulting geologists in the basin. Several of these proprietary files may be purchased in digital form. Large commercial organizations such as Petroleum Information Corporation (PI) and Dwights Data Corporation have compiled very few oil and gas production records for the Appalachian basin.

In May 1994, the Ohio Division of Geological Survey provided the USGS with an 11,000 well digital production file to assess Clinton/Medina sandstone gas plays for the 1995 National Assessment of oil and gas. Production data from 1972 through 1986, organized by county, township, formation, well, and field, are recorded in this data file. Since then, the Ohio Survey has increased their oil and gas production file to about 37,000 wells. A major activity for FY95 was to identify and acquire well production data in the States of New York and Pennsylvania and to acquire the update of the production data base in Ohio.

Approximately 37,000 annual production records from 10,000 wells in 6 counties in western New York State were acquired from the New York State Department of Environmental Conservation (Bureau of Oil and Gas Regulation, Division of Mineral Resources) in early 1995. The records extend from 1985 through 1994 and are organized by county, township, formation, field, and well. Production data as far back as the early 1960's are stored on paper records but have not yet been converted to digital form. An additional 6,000 well records were acquired in the 6 counties of western New York for which no production records are available. Also in early 1995, deep reservoir production data consisting of 32,000 wells in 5 counties in northwestern Pennsylvania was acquired from the Pennsylvania Topographic and Geologic Survey. These data record oil and(or) gas production from units below the Middle Devonian Tully Limestone and are organized by County, 7.5 minute quadrangle, formation, field, and well. Because of a five-year confidentiality clause, the data file is restricted to annual gas production from 1980 through 1989. Annual updates will be made available for New York and Pennsylvania production records through the respective State agencies. The 26,000 well, production-records update in Ohio is still being compiled and edited by the Ohio Division of the Geological Survey and should be available to interested users in early 1997.

The New York, Ohio, and Pennsylvania production files are presently stored in the USGS Wells database. To date, an evaluation of these production records has been limited to selected wells in eastern Ohio where EUR's were calculated for the 1995 National Assessment. Decline curve analysis is planned for wells along or nearby the transects so that their gas yields can be compared with stratigraphic and structural characteristics of the "Clinton" sands and Medina Group sandstones.

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