Well Production and Water Management

After a well is completed, operators can begin producing the fluids from the well.

Natural Gas Production

After a well is completed, operators can begin producing the fluids from the well. Natural gas and water move from the formation into the well, with the gas initially flowing to the surface by reservoir pressure. If necessary, later in the life of a well, the operators will install plunger lift pumping systems to produce the natural gas.

The combined fluids are passed through a separator, which segregates the fluids into a natural gas stream and a water stream. The volume of natural gas is measured by a sales meter near the wellhead. The gas is collected through a series of gathering lines and may be stored in tanks or immediately sent off of the lease to a central pipeline or a gas-processing facility.

The estimated life of these wells is 20 to 30 years. If production declines in a few years, additional frac jobs may be undertaken to restimulate the wells.

Water Management

Water is generated in three ways — ground water, flow-back water, and produced water. First, the borehole passes through shallow water-bearing formations as the upper portion of each well is drilled with an air drilling rig. As a result, a substantial amount of ground water collects in the wellbore. This relatively clean water is collected and treated with an aluminum-based flocculant. If the chloride concentration in the water is less than 1,500 ppm, the Arkansas Department of Environmental Quality (ADEQ) allows the water to be applied to roads for dust control.

A large volume of water is used to make up the frac fluid. Much of the water flows back out of the well because of subsurface pressure immediately following the frac job. The initial flow is collected in frac tanks parked on the well site. One operator typically attempts to reuse this water for subsequent frac jobs; however, this becomes more difficult as salts and other contaminants build up in the water with each reuse. Typically, flow-back water can be reused 3 to 4 times, but in some situations, it can be reused as many as 8 times.

Frac Tank Click to enlarge

However, a significant volume of water comes out of the well at a slower rate over an extended period of time. The Fayetteville Shale generates very little produced water (i.e., water naturally in the shale rock along with the gas). The combined water flowing out of the well when the well is producing gas is a blend of flow-back water and produced water. This is collected in an onsite water storage tank. The tank is pumped out periodically by vacuum trucks, which haul the water offsite for disposal. If this production-phase water has a chloride concentration less than 5,000 ppm, it can be sent to a land application site. If the chloride concentration exceeds 5,000 ppm, the water must be transported to commercial disposal wells, most of which are located far from the active natural gas wells. The cost of disposing of the high-chloride water, including transportation, can exceed $6/bbl, which is very expensive. The large Fayetteville Shale operators are beginning to drill some of their own water disposal wells that are closer to their active sites.

Water Storage Tank Click to enlarge

FOR MORE INFORMATION:

• Technologies that can minimize the environmental impacts of well production and water management.
  
  
• Regulatory requirements associated with well production and water management.