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

SUMMARY OF FY95 ACCOMPLISHMENTS

1. Three regional transects have been drawn through selected parts of New York, Ohio, and Pennsylvania to show the stratigraphic, facies, and sequence stratigraphic framework of the Niagaran Series (Medina, Clinton, and Lockport Groups and equivalent strata).

2. New facies and sequence stratigraphic interpretations are suggested for sandstones of the Medina Group in western New York State. One new interpretation is the sequence boundary within the Grimsby Formation. This proposed sequence boundary resulted from broad valleys cut into emergent, progradational shoreface sandstone (highstand tract deposits) and backfilled by fluvial and tidal sandstone (transgressive tract deposits) during a rise in sea level.

3. Several thousands of gas production records for individual wells have been acquired in digital form for six counties in New York and five counties in Pennsylvania. These production records are stored on the USGS Wells database.

4. A land-use and land-cover map with political boundaries was compiled at a scale of 1:500,000. Also included on the map are boundaries of Clinton/Medina/Tuscarora oil and(or) gas plays and 1/4 sq mi cells showing the distribution of wells that penetrate the Clinton/Medina/Tuscarora interval and their hydrocarbon status.

5. An oil and gas field map was compiled for the "Clinton" sands, Medina Group sandstones, and Tuscarora Sandstone at a scale of 1:500,000.

6. A preliminary map showing structural contours has been constructed for the study area at a scale of 1:500,000 using the Dynamic Graphics Inc. Interactive Surface Modeling (ISM) system and WHCS data files.

7. A comprehensive literature search was made for structure below the Upper Silurian Salina Group salt in the play area to identify potential structural elements that may control fracture patterns in Clinton/Medina sandstone reservoirs.

8. A working hypothesis suggests that the Clinton/Medina sandstones and the equivalent Tuscarora Sandstone in the Appalachian basin should have three pressure domains; a normally pressured domain, a low-pressured domain, and a high-pressured domain. The normal and underpressured domains have been verified by project investigations in FY95. The postulated overpressured domain has yet to be verified but there are some indications that the Tuscarora Sandstone reservoirs in central Pennsylvania may be overpressured.

9. Wells that produce or have produced water from the "Clinton" sands, Medina sand, Medina Group sandstones, and Tuscarora Sandstone were compiled on a preliminary map. These maps will be used to better define the boundary between continuous-type and discrete hydrocarbons accumulations in the Clinton/Medina sandstone reservoirs.

10. Several hundred published and unpublished analyses for brines and formation waters in the Clinton/Medina sandstone reservoirs were compiled and loaded into a USGS database.

11. Burial, thermal, and petroleum generation history models were generated from data in six deep drill holes in Ohio and West Virginia to estimate paleotemperatures of the "Clinton" sands and Tuscarora Sandstone and to test the feasibility of the Middle Ordovician Utica Shale as the source of the gas in the "Clinton"/Medina/Tuscarora interval. These models suggest that the Utica Shale, located 1,000 to 1,400 ft beneath the Clinton/Medina/Tuscarora sandstones, is a plausible source of the gas.

12. Seismic profiles were located in New York, Ohio, and Pennsylvania that may help to identify local and regional structures capable of generating tectonic fractures in the "Clinton" sands, Medina Group, and Tuscarora Sandstone .

13. Environmental issues were investigated to evaluate the impact of high drilling density and local brine disposal associated with extracting gas from a continuous-type accumulation.

14. An extensive selected bibliography was compiled for literature regarding the geology and oil and gas resources of the "Clinton" sands, Medina Group, and Tuscarora Sandstone in the Appalachian basin.

15. The preliminary results of this project generally support the Lower Silurian Clinton/Medina/Tuscarora sandstone plays as defined for the 1995 National Assessment and the assessment methodology applied to them.

a. The characterization of the Clinton/Medina sandstone gas plays (6728-6731) in the 1995 National Assessment as a part of a continuous-type gas accumulation is justified. Moreover, the assessment methodology applied to these plays--which accounts for regionally extensive, gas-saturated reservoirs--is appropriate.

b. The Clinton/Medina sandstone oil/gas play (6732) in the 1995 National Assessment, that adjoins the continuous-type gas accumulation plays on the west, seems to be appropriately defined as a conventional oil and gas play having discrete accumulations. However,the trapping mechanism(s) of the oil and gas in the conventional play and the limits of the transitional boundary between the conventional and continuous-type (unconventional) plays remain poorly known.

c. The Tuscarora Sandstone gas play (6727) in the 1995 National Assessment, that adjoins the continuous-type gas plays on the east, may need to be revised. Sparse pressure and temperature data suggest that this play may be a continuous-type gas play rather than a conventional gas play as originally suggested in the 1995 National Assessment. More data are needed to support the new interpretation.

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