Overview of Shale Gas Water Issues

Tens of thousands of wells are being drilled each year in several large gas shale formations in the United States. Shale gas development is also beginning in other countries and will likely increase rapidly. All U.S. shale gas wells must be fractured to allow sufficient gas to be produced to make the wells economically viable. In order to conduct fracturing operations, gas companies must obtain several million gallons (5,000 to 20,000 m3) of water for each well from local sources. In some areas, the available freshwater supplies are limited, creating a challenge for the gas companies. After the frac job is finished, a portion of the frac fluid that was injected returns to the surface over the next few days. This “flowback water” is considerably saltier than the original frac fluid, plus it often contains elevated concentrations of metals, radionuclides, and other contaminants. This paper describes the water needs for making up the frac fluids for each well and how the necessary volume compares with other existing water uses in those regions. The steps in the shale gas process in which water is used and wastewater is generated are discussed, with an emphasis on management of the flowback water and smaller volumes of ongoing produced water from the shale formation. Various chemical additives are mixed with water and proppants to make frac fluids. The paper describes the general categories of chemicals that are used and provides information on the Frac Focus chemical registry developed to provide public access to the names and quantities of chemicals actually used in the frac fluids for many U.S. shale gas wells.