Closed loop system
A closed loop system consists of using a small waste-water processing system on the well site. It removes pollutants from the frac water as well as additional water that may also be present in the formation itself--all of which flows back up a well.
Waste water is pumped directly into steel storage containers and held for processing.
Solids extracted from the water by this method are removed by truck to a waste treatment station for disposal. Treated water that remains after on-site processing may then be reused on a later frac job. Typically, up to 50 percent of the frac water can be recovered and reused. It can be reused up to a dozen times without treatment.
Less waste water needs to be moved off site, and less water is required for additional drilling operations. This method generally lowers total drilling cost, as well as the amount of water used and its cost. It also contributes to higher drill rates which provides cost savings.
According to a news item that appeared in February, 2010 Chesapeake Energy, the most active driller in the Marcellus shale, has frequently used closed loop systems for handling drilling waste water in its Pennsylvania operations.
In November, 2010 Chief Oil and Gas announced that it too had switched to closed loop for all of its wells.