The Marcellus Play is in its early stages of development and there is little data on the role that geology may play in controlling gas-in-place and, ultimately, proven reserves. In particular, the extent to which the Marcellus has been fracture may be of utmost importance in gas production. Below is a list of geological parameters that may control or contribute to ultimate reserves with some of these parameters having a direct bearing on the development of natural fractures.

A.) Structural position: The Marcellus occupies at least three structural positions on the Appalachian Plateau and it is reasonable to expect that the quality of the gas seal may vary among these postions: 1.) within the wedge faults that define plateau anticlines, 2.) associated with deep basement structures that are not manifest as first order plateau anticlines, 3.) in the relatively undeformed plateau detachment sheets between plateau anticlines.

B.) Overburden compaction: The volume of free gas correlates with porosity that is lost through overburden compaction. The controlling parameters for overburden compaction include at least: 1.) the depth of burial, 2.) compaction disequilibrium, 3.) present formation pressure.

C.) Tectonic compaction: (better known as layer-parallel shortening strain): The plateau detachment sheet increases from < 5% layer-parallel shortening in the outer reaches of the plateau (e.g., Mercer County, PA) to more than 10% layer-parallel shortening (e.g., Potter County, PA) to even high strain near the Allegheny Front (e.g., Clearfield County, PA). Porosity, hence, free gas-in-place may vary as a function of tectonic compaction.

D.) Abnormal pressure: Reservoir pressure controls the volume of free gas through compressibility. The mechanisms of generating abnormal pressure in the Marcellus could include: 1.) Compaction disequilibrium, 2.) hydrocarbon maturation, 3.) tectonic compaction, and 4.) transformation of smectitc to illite. Different mechanisms contribute differently to the gas-water ratio in the Marcellus.

E.) Formation thickness: The Marcellus is less than 50 feet thick towards the edge of the basin and increases to above 200 feet thick near the Allegheny Front of PA. The variation in TOC as a function of formation thickness is virtually unknown at present.

F.) Quartz to clay ratio: The ratio of free gas to adsorbed gas varies with the quartz to clay ratio.

G.) Thermal maturation: Outcrop measurements demonstrate that fracture density increases with thermal maturation. By the observation fracture density will vary with depth of burial.

H.) Burial History including depth of burial: Portions of the Marcellus pass through the oil window in the period 310-300 Ma when the Appalachian Basin was subject to a basin-wide ENE stress field. This produced a certain style and density of jointing that is more likely in the deeper portions of the Marcellus play.

I.) Systematic variation in properties from bottem to top of the Marcellus: Fracturing as a function of TOC which is highest at the bottom of the black shale units.

J.) Completion style: Foam fracs are used when gas shales are naturally fractured and slickwater fracs are used when the shale is unfractured. The shale, itself, may have different properties depending on whether it contains dense natural fractures.

At present the behavior of each of above as it affects the Marcellus is a geological enigma. By collaborating with industry Appalachian Fracture Systems, Inc. is working on solutions to these geological enigmas, particularly as they pertain to the development of natural fractures.