Most onshore wells drilled today must be hydraulically fractured during completion to economically produce
natural gas and petroleum liquids. This is particularly the case in tight reservoirs, such as deep shale. After the
hydraulic fracturing process is completed, frac fluids, which are comprised of more than 98% water and sand, are allowed to flow back to the surface for recovery. This flowback operation is often referred to as “cleaning up the well.” Flowback can last from a few hours to several days. During this time, natural gas and oil which flows back with the fluids may contain volatile organic compounds (VOCs) such as propane. Each state has state implementation plans (SIPs) that are approved by the
Environmental Protection Agency (EPA). Rules promulgated under the SIPs ensure that minor and temporary sources of emissions, such as well completions, do not cause or contribute to violations of federal air quality standards.1
In addition,
Chesapeake utilizes a voluntary procedure called "reduced emissions completions," or “green completions,” to control or reduce VOC emissions. A reduced emission completion can eliminate most of the VOC emissions and recover valuable natural gas during flowback and well testing.2 Reduced emission completions are not, however, available for every well that is drilled and completed, as they require special equipment and the installation of a natural gas gathering line and sales meter prior to well flowback and testing.
In August 2012 the EPA published a final rule, 40 CFR Part 60 Subpart OOOO, which requires all future combustible flowback emissions from hydraulic fracturing completions be flared or captured using a reduced emissions completion. Beginning on October 15, 2015, all combustible flowback emissions must be captured using a reduced emissions completion, with very limited exceptions when such a completion is not possible or can cause a fire hazard.
A typical natural gas wellsite may have a two-phase separator that is used to separate produced water from the natural gas. In that case, the produced water is stored on-site until it can be removed by truck and little, if any, VOCs are emitted from the stored water. When wells produce natural gas or petroleum liquids that are rich (i.e., contains heavier hydrocarbons, such as propane, butanes, pentanes, etc.), the wellsite may have a three-phase separator, called a heater treater, which separates produced water, natural gas and petroleum liquids. In this case, the petroleum liquids are also stored on-site until removed by truck or by pipeline.
VOCs may be emitted from liquid petroleum storage tanks and then vent to the atmosphere. Each state has rules that determine allowable VOC emissions, permitting requirements and emissions thresholds at which equipment, such as a flare or other emissions control device like a vapor recovery unit (VRU), must be used. When technically and economically feasible, Chesapeake prefers to control VOC emissions with a VRU in order to reduce emissions and recover valuable natural gas.3 In addition, beginning October 15, 2013, all liquid petroleum storage tanks will be required to meet strict VOC emissions limits in accordance with Subpart OOOO.
Footnotes
1. 40 CFR Part 50 – National Primary and Secondary Ambient Air Quality Standards.
2.
http://www.epa.gov/gasstar/ (see Green Completions – PRO Fact Sheet No. 703).
3.
http://www.epa.gov/gasstar/ (see Lessons Learned– Installing Vapor Recovery Units on Crude Oil Storage Tanks).