Underground rock layers generally contain fluids such as formation water, oil, natural gas or some combination of these fluids. During natural gas production, this naturally occurring formation water can travel through the wellbore and up to the surface. This water is referred to as produced water. The salt content, total dissolved solids and overall quality of produced water varies based on geologic basin and specific rock strata, the makeup of which is dependent on whether natural gas or crude oil is being produced. Produced water generally includes a mixture of either liquid or gaseous hydrocarbons, formation water, salts, suspended solids (sand and silt) and very small amounts of other additives that may have been used during production activities. After initial production, the salt content of produced water can vary from slightly higher than that of freshwater to up to 10 times higher than that of seawater.
Produced Water Management
The management of produced water presents many challenges and can pose significant costs to operators. Operators are careful to manage produced water in ways that protect surface and groundwater resources. Whenever possible, operators seek to reduce future demands for freshwater by examining both traditional and innovative approaches to reuse or recycle by using it in other production processes. Current techniques include a variety of methods such as underground injection, treatment and discharge, evaporation, reuse and recycling.
Underground injection has historically been the primary disposal option for produced water by the natural gas and oil industry. This process uses saltwater disposal wells (SWDs) to return the water underground into porous rock formations similar to those from which it came. These formations are separated from treatable groundwater by thousands of feet of multiple layers of impermeable rock. SWDs are permitted under the Federal Safe Drinking Water Acts’ Underground Injection Control Program. Underground injection of produced water is not, however, always possible, as suitable injection zones may not be available. In those cases, produced water can be managed through reuse (filtration and blending), advanced process recycling (chemical treatment followed by distillation), waste reduction (via evaporation) or processed through water treatment facilities and surface discharged.