Reduced Emission Well Completions and Workovers

Well completion is the process of bringing an oil or natural gas well into production after drilling or workover has been completed, which may involve flaring or substantial venting of methane from hydraulically fractured gas wells. A reduced emissions completion (REC) is a practice that employs specially designed equipment to capture gas produced during well completions and well workovers following hydraulic fracturing and deliver it to the sales line. This practice is also commonly referred to as a reduced flaring completion or green completion. RECs reduce emissions of methane, volatile organic compounds (VOCs), and hazardous air pollutants (HAPs) during well cleanup and can eliminate or significantly reduce the need for flaring.

Completion of a hydraulically fractured well involves back-flow of the frac fluids which is a multi-phase flow (i.e., gas, water, condensate, and sand) at high flow rates that may not be handled by long-term production wellhead equipment. A reduced emissions completion employs specially designed separators to remove sand and liquids (i.e., water and gas condensate) from the natural gas to deliver into the sales line or flared. To conduct a REC, portable separators and piping are brought on site following the hydraulic fracture for periods typically between 1 and 30 days, as required, to clean up the wellbore and reservoir. 

The following are descriptions of specially designed and sized equipment required for a REC: 

• Plug catchers: used to remove any large solids, such as drill cuttings, that could damage the other separation equipment.  
• Sand traps: used to remove the excess proppant present in the flowback stream.  
• Three-phase separator: used to remove free water and gas condensate or oil from the gas. 
• Dehydrators: used to remove water vapor from the produced gas before it enters the sales pipeline, if necessary, depending on the gas gathering system. Normal wellhead dehydrators may be sized to process the backflow gas.  
• Temporary piping: used to connect the well to the REC equipment and gathering system if the permanent piping is not yet in place. 
• Sales meter: if not already in place, a sales meter must be installed to measure the gas sales for proper royalty credits. 

Oil and gas well completions are commonly conducted using REC equipment prior to installation of the permanent production separator.

Wells that require hydraulic fracturing to stimulate or enhance gas and oil production may require a lengthy completion, and therefore are good candidates for RECs. Lengthy completions mean that a significant amount of gas may be vented or flared; this gas could potentially be recovered and sold for additional revenue. REC equipment could be shared between newly developed fields that have many wells drilled in close proximity to minimize transport, set-up, and equipment rental costs. 

Energized Fracturing: RECs can also be performed in combination with energized fracturing, wherein inert gas (e.g., CO₂ or nitrogen) is mixed with the fracturing water under high pressure to enhance the process of fracturing the formation. The process is generally the same with the additional consideration of the composition of the flowback gas. The percent of inert gases in the flowback gas is, at first, unsuitable for delivery into the sales line, but as the fraction of inert gases decreases, the gas quality becomes be suitable for injection into the sales line. A portable membrane acid gas separation unit can further increase the amount of methane recovered for sales after a CO₂ energized fracture.  

Gas Lift: In low pressure (i.e., low energy) reservoirs, RECs are often carried out with the aid of compressors for gas lift. Gas lift is accomplished by withdrawing gas from the sales line, boosting its pressure, and routing it down the well casing to push the fracturing fluids up the tubing at high enough rates to expel the frac fluids. The increased pressure facilitates flow into the separators and then the sales line where the lift gas becomes part of the normal flowback that can be recovered during an REC.

Methane emission reductions can be determined by taking the difference in emissions from the source before and after the specific mitigation action was applied. While using actual measurements may provide a more accurate representation of emissions/reductions from individual equipment at a given time, methane emissions can also be reasonably calculated by using emission factors. When replacing a normal well completion with an REC, this means calculating emissions from a normal well completion and subtracting emissions from an REC. Emissions reductions from RECs can be estimated using emission factors representing REC and non-REC scenarios from the Natural Gas Systems section of the Inventory of U.S. Greenhouse Gas Emissions and Sinks (“Greenhouse Gas Inventory”, or “GHGI”). These emission factors are based upon reported subpart W data and are uniquely calculated each year and highly variable from year to year. 

ER = C × (EF_NR – EF_R)  

Where: 

ER = Emissions reduction estimate (kg CH₄/yr) 

C = Number of completions (events/yr) 

EF_NR = Emission factor (kg CH₄/non-REC completion event) 

EF_R = Emission factor (kg CH₄/REC completion event) 

Assumptions/Constants: 

• Use the most current “non-REC completions” and “REC completions” emission factors. Emission factors are generally developed to be representative of long-term averages for all applicable emission sources. EPA updates the emission factors from the Natural Gas Systems section of the Inventory of U.S. Greenhouse Gas Emissions and Sinks (“Greenhouse Gas Inventory”, or “GHGI”) every year, so specific emission factors may change. To find the current emission factor, navigate to the GHGI website for Natural Gas and Petroleum Systems and click on the page for the most recent inventory. On that page, you will find links for Annex 3.5 (Methodology for Estimating CH₄, CO₂, and N₂O Emissions for Petroleum Systems) and Annex 3.6 (Methodology for Estimating CH₄, CO₂, and N₂O Emissions for Natural Gas Systems). Methane emission factors can be found in Table 3.5-3 (Petroleum Systems) and Table 3.6-2 (Natural Gas Systems). 

The calculation methodology in this emissions reduction section is based upon current information and regulations (as of August 1, 2023). EPA will periodically review and update the methodology as needed.

In addition to reducing emissions of methane, employing reduced emission completions may: 

• Increase revenue: Valuable gas and condensate from the REC may be captured and generate additional revenue. 
• Reduce clean-up activities: Drilling waste clean-up will be minimized when the hydraulic fracturing fluids are not directed to an impoundment or tank.

IPIECA. (2014, February 1). Green completions. https://www.ipieca.org/resources/energy-efficiency-solutions/units-and-plants-practices/green-completions-2014/