The Lower Silurian regional oil and gas accumulation was named by Ryder and Zagorski for a 400-mi (mile)-long by 200-mi-wide hydrocarbon accumulation in the central Appalachian basin of the Eastern United States and Ontario, Canada). From the early 1880s to 2000, approximately 300 to 400 million barrels of oil and eight to nine trillion cubic feet of gas have been produced from the Lower Silurian regional oil and gas accumulation. The dominant reservoirs in this regional accumulation are the Lower Silurian “Clinton” and Medina sandstones in Ohio and westernmost West Virginia and coeval rocks in the Lower Silurian Medina Group (Grimsby Sandstone/Formation and Whirlpool Sandstone) in northwestern Pennsylvania and western New York. A secondary reservoir is the Upper Ordovician(?) and Lower Silurian Tuscarora Sandstone, a more proximal eastern facies of the “Clinton” sandstone
and Medina Group in central Pennsylvania and central West Virginia. The Tuscarora Sandstone consists of a greater percentage of net sandstone than the “Clinton”-Medina interval and typically the Tuscarora sandstones are coarser grained.
The Lower Silurian regional oil and gas accumulation is subdivided by Ryder and Zagorski into the following three parts: (1) an easternmost part consisting of local gas-bearing sandstone units in the Tuscarora Sandstone that is included with the basin-center accumulation; (2) an eastern part consisting predominantly
of gas-bearing “Clinton” sandstone-Medina Group sandstones having many characteristics of a basin-center accumulation; and (3) a central and western part consisting of oil- and gas-bearing “Clinton” sandstone-Medina Group sandstones that is a conventional accumulation with hybrid features of a basin-center accumulation. Whereas the supply
of oil and gas in the central and western hybrid-conventional part of the regional accumulation continues to decline because of the many wells drilled there since the late 1880s, except in the Lake Erie offshore, new gas continues to be discovered in the deeper, eastern basin-center part. In the easternmost part, only small quantities of gas have been produced from the Tuscarora Sandstone because of its generally poor reservoir quality and because of the low energy (Btu) content
of the gas. Much of the gas produced from the Tuscarora Sandstone is trapped in fractured reservoirs.
In order to better understand the character and origin of the Lower Silurian regional oil and gas accumulation and its component
parts, six cross sections were drawn through parts of New York, Pennsylvania, Ohio, and West Virginia. The locations of the cross sections are shown, and results have been reported. Each cross section shows the stratigraphic framework, depositional setting, sequence stratigraphy, and hydrocarbon-producing intervals of the Lower Silurian sandstone reservoirs and adjoining strata. Cross section E–E′ discussed in this report is about 235 mi long, trends northwestward approximately normal to the depositional strike of the Lower Silurian sandstone system, and extends through large stretches of the eastern basin-center and central and western hybrid-conventional parts of the Lower Silurian regional oil and gas accumulation. Of the remaining five cross sections, four trend northwestward (approximately normal to the depositional strike of the Lower Silurian sandstone system) and one (A–A′) trends north-northeastward
(parallel to and, in part, oblique to the depositional strike). Several of these cross sections (E–E′ and F–F′) traverse the entire Lower Silurian regional oil and gas accumulation. |
