Flareless or “green” completions reduce flaring and venting of natural gas from oil and gas wells.
Before natural gas and coalbed methane wells begin producing gas for sale, the well bore and surrounding reservoir must be “cleaned up” (i.e., any fluids, sand, coal particles, or drill cuttings within the well bore must be removed). The conventional method for doing this is to pump air down the well, which lifts the waste fluids and solids out. The solid and liquid waste materials are then dumped into a pit or tank, and any gas that is removed is flared or vented to the atmosphere. In some flareless or green completions, natural gas, rather than air, is pumped down the well bore to clean it out.
In flareless or green completions the gas that comes to the surface is separated from fluids and solids using a series of heavy-duty separators (sometimes referred to as “flowback units”). The water is discharged to tanks to be reused, the sand is sent to a reserve pit, and the gas is either cycled back through the well bore, or sent to a pipeline to be sold rather than vented or flared.
According to the EPA, benefits of this system include: the elimination or reduction in venting or flaring of natural gas; sale of the gas and condensate provides the operator with an immediate revenue stream; there is a reduction in solid waste and water pollution; and the system enables safer operating practices. Green completions also reduce methane emissions, a potent greenhouse gas.
An analysis of green completions by Goldman Sachs and NRDC found that an investment of $8,700 to $33,000 per well led to a methane capture rate of 7,000 to 23,000 Mcf/well with a profit of $28,000 to $90,000 per well and a payout in < 0.5 – 1 year. EPA says payout could take as few as 60 days.
An alternative to sending the gas to the pipeline is to send it to a flare tank. Flare tanks capture and more fully combust the waste gases. The tanks can be carried from site to site. This practice avoids the costs associated with excavating and reclaiming flare pits, and avoids the potential liability associated with cleaning up soils contaminated by flaring.
In 2012, EPA issued a final rule on for New Source Performance Standards and National Emission Standards for Hazardous Air Pollutants. The rule requires green completions at new wells 'drilled principally for production of natural gas,' exempting those drilled for oil. The rule does not apply to existing wells.
At the time of the rulemaking EPA Administrator Gina McCarthy said that 50% of wells used green completions.