MARCELLUS FLOWBACK WATER GEOCHEMICAL CHARACTERISTICS FOR TREATMENT AND DISPOSAL OPTIONS

Natural gas development from unconventional shale reservoirs, such as the Marcellus shale, requires large volumes (3 to 7 million gallons) of water mixed with sand proppant and specialty chemical additives, which are injected at high pressure to hydraulically fracture the relatively impermeable shale reservoir. The hydraulic fracturing operation is designed to open fractures in the shale and thus stimulate the flow of natural gas that is contained within the shale. The Marcellus shale is an organic-rich black shale deposited in a marine environment, and therefore contains salts, metals, uranium, and thorium, among other constituents. Once the hydraulic fracturing operation has been conducted on the natural gas shale well, a volume of the injected fluids, typically 10 to 20%, will return to the surface via the well. The fluids that return to the surface are commonly known as flowback water until the well is put on online, at which point the fluids are known as produced water. The flowback or produced waters typically have elevated concentrations of salts and metals, including barium and strontium, that were dissolved from the marine deposit, thus resulting in a fluid with concentrations of total dissolved solids commonly greater than 100,000 mg/L. In addition, relatively low levels of naturally-occurring radioactive material, commonly known as NORM, are also contained in the flowback and produced waters, consisting primarily of radium-226, radium-228, and radon-222. A comprehensive understanding of the origin, occurrence, and concentration of these constituents is necessary to ensure that the proper treatment and methods are utilized prior to reuse or disposal.