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

ENVIRONMENTAL IMPACT ASSOCIATED WITH DEVELOPMENT OF CONTINUOUS GAS ACCUMULATIONS

The high drilling density required to develop continuous gas accumulations can have a great impact on the environment. Visual impacts related to dense well spacing include those created by access roads, pipelines, and well locations. In many cases, the amount of land disturbed can be minimized through the early identification of the accumulation type and size. First, a well-designed access and transportation network should be planned in advance. Where several operators are developing the accumulation, a cooperative planning and construction effort is desirable to reduce visual impact and costs. Secondly, surface impact can be reduced by having several wells share a single-well location. Having multiple wells at a single location is accomplished by directional drilling techniques. Also, visual impact can be reduced by locating well sites, roads, and pipelines in areas that are visible only over short distances such as in ravines and behind small hills.

Water production may be associated with continuous gas accumulations but it is low in comparison to that in conventional and coalbed gas accumulations. This water production, which generally is less than 10 barrels of water a day for the Clinton/Medina sandstone reservoirs, must be disposed of in a safe and economical manner. The free water is separated from the gas stream by a separator whereas molecular water is commonly separated from the gas stream by glycol dehydration. Current disposal methods include reinjecting the water, evaporation, creating wetlands, or hauling it to a treatment plant. The amount and quality of the water dictate the method used. Reinjecting the water is accomplished either by using a nonproducing well, or drilling a new well. The water may be reinjected into the same formation from which it was produced or into a different formation that is isolated from water aquifers used for domestic, agricultural, or industrial purposes. In some areas, the water is discharged into the local drainage system and, in at least one case, in the Green River Basin of Wyoming, it is used to create a wetland. Also, the water can be stored in tanks at the well site and hauled to a common treatment and disposal site.

A study by Callaway (1987) indicates that in New York State there is little between-well variation in the quality of formation water produced from a given reservoir. Forty-six of the eighty-six water samples used in the study were collected from Medina Group sandstones. Previous studies indicating significant between-well variation in the quality of formation water were based on a large number of samples, many of which were inconsistently sampled and analyzed. For example, analyses from numerous labs failed to meet basic ionic and mass balance checks. Water samples utilized by Callaway (1987) indicate that 98% of their dissolved solids, ranging from 10,000 to 25,000 ml/l, are accounted for by sodium, calcium, magnesium, potassium, and chloride. The addition of barium and strontium to this list of elements accounts for over 99% of the dissolved solids. Similar high dissolved solids and chemical constituents are recorded in formation waters in Medina Group sandstones in Pennsylvania (Young and others, 1991; Siegel and others, 1990) and "Clinton" sands in Ohio (Breen and others, 1985).

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