Sampling and Analysis of Water Streams Associated with the Development of Marcellus Shale Gas

At current estimates of recoverable natural gas of more than 489 tcf, the Marcellus Shale is considered to be among the largest natural gas reserves in the world. The development of this resource is technology driven, involving the use of hydraulic fracturing technology as one of the necessary initial steps to releasing natural gas from shale rock. Sustainable development of shale gas in the Marcellus Play requires the management of volumes of water in a manner that is protective of human health and the environment. Typically, 1 - 4 million gallons of an aqueous influent stream bearing very low concentrations of additives are introduced downhole during each well completion. These additives may include friction reducers, corrosion inhibitors, oxygen scavengers, scale inhibitors and biocides that can be blended into the water and sand mixture, but make up less than 0.5 percent of the total frac fluid that is injected into a drilled well at high pressures to achieve and maintain the fracture of the shale rock. Following fracturing, flowback water is collected from the well and placed into frac tanks and/or flowback impoundments. Effective management of flowback water requires some level of knowledge of the characteristics of the water. Flowback water contains salts, metals and organic compounds from the formation and the compounds that were introduced as additives to the influent stream. Discussions between the industry and regulatory agencies of Pennsylvania and West Virginia have pointed to the need for an information base on the composition and properties of flowback water and on the influent water streams that are used to perform frac jobs. The objective of this effort was to conduct the initial sampling and analysis of water streams associated with shale gas development in the Marcellus Shale. In recognition of the importance of this effort, 17 member companies of the Marcellus Shale Coalition (MSC) volunteered 19 locations where shale gas wells were scheduled to be hydraulically fractured. The Field Sampling and Analysis Plan and the Quality Assurance Project Plan were developed, reviewed, and finalized for the effort by the 7 companies of the Appalachian Shale Water Conservation and Management Committee (ASWCMC), Pennsylvania Department of Environmental Protection (PADEP) and West Virginia Department of Environmental Protection (WVDEP). At each of the host sites, samples of influent water streams at Day 0 and the flowback water streams at 1, 5, 14, and 90 days following the frac job event were collected by a single engineering subcontractor, URS. All samples were sent to Test America (a PADEP and WVDEP certified environmental testing laboratory) for analyses. The list of constituents recommended for the characterization study was developed from comments received from the PADEP, the WVDEP and members of the ASWCMC. Categories of determinations that were conducted included: 1) General Chemistry, 2) Organic Compounds, and 3) Metals. Once reviewed and qualified, data from these analyses were organized and tabulated in a source blind manner into an Excel spreadsheet that currently represents the information base. Results from this effort indicates that values for pH, alkalinity, total dissolved solids (TDS), total organic carbon (TOC), oils and greases and other parameters from general water characterization are within the normal ranges reported for conventional produced waters by the USGS. Flowback water concentrations of TDS ranged from 680 to 345,000 mg/l; typical profiles show an increase in TDS in flowback water with time following a frac job event. As with conventional produced water, shale gas flowback water cations are dominated by sodium and calcium; the main anion is chloride. Metals normally seen in conventional produced waters, such as iron, calcium, magnesium, and boron, are at levels in flowback waters that are well within known ranges for normal produced waters. Heavy metals that are of concern in urban industrial wastewaters and POTW sludges --- such as chromium, copper, nickel, zinc, cadmium, lead, arsenic and mercury --- are at very low levels. Among volatile organic constituents (VOCs), approximately 96% of the constituent determinations were at non-detectable levels and less than 0.5% were detected above 1 ppm. VOCs that are measurable are those that are normally found in conventional produced waters. Regarding semi-volatile organic constituents (SVOCs), more than 98% of the determinations were at non-detectable levels and less than 0.03% of all the constituents were above 1 ppm; and several constituents were at low trace levels– 8 usually below 10 ppb. Pesticide concentrations measured in the samples were extremely low (all results were less than 1 ug/L) and extremely random with results occurring in some supply water, Day 0, Day 14 and Day 90 samples. It is possible that these low level concentrations are not representative of actual conditions and may be attributed to laboratory contamination or instrument noise. In conclusion, the results of this shale gas water characterization effort indicate that all pesticides, PCBs, and a large fraction of the VOC and SVOC should be considered to be unnecessary for the sampling and analysis of flowback waters in the future.

Tags: Fluid interaction, Fluids, Geochemistry, Geology, hydraulic fracturing, marcellus shale, rock-water interaction, task 9