New technology is making it possible to develop resources in a manner that is cost-effective, economically viable and safe. Wells can now produce natural gas for up to 30 years.
Natural gas processing
The natural gas purchased by consumers consists almost entirely of methane, the simplest hydrocarbon. In gas reservoirs, however, the methane is typically found in mixtures with natural gas liquids - such as ethane, propane, butane and pentanes - as well as water vapour, hydrogen sulphide, carbon dioxide, nitrogen and other gases. Natural gas that contains hydrogen sulphide is referred to as "sour gas," while natural gas without hydrogen sulphide is called "sweet gas."
The natural gas liquids and other substances are removed from the gas stream at processing plants located near production areas or at "straddle plants" located on major pipeline systems.
Of the more than 650 natural gas processing plants in Alberta, more than 50 are large facilities that produce sulphur as a byproduct of the hydrogen sulphide in sour gas. Hydrogen sulphide is flared, incinerated or reinjected back into a reservoir.
The British Columbia sour gas industry includes three large sulphur-recovery plants and six smaller field plants. Additionally, smaller volumes of sour gas are produced and processed in the Northwest Territories, Saskatchewan, Manitoba and Ontario. The Deep Panuke discovery off Nova Scotia also contains hydrogen sulphide, which will be removed from the gas stream and injected into a deep geological formation. Gas reinjection is also being examined in other areas as means of meeting air quality objective and reducing greenhouse gas emissions.
Removing liquids and sulphur
The raw natural gas from wellheads may pass through compressors to maintain or increase pressure and may be heated to prevent freezing and condensation. Glycol dehydrators are typically used to remove water from natural gas streams, although our industry has been developing alternative technologies to reduce emissions.
In processing plants, gas is chilled to separate the natural gas liquids from methane. The hydrogen sulphide is removed by a chemical reaction in the presence of catalysts. The natural gas that comes out of the plants meets pipeline specifications for dry gas, but may still contain natural liquids, which are removed at straddle plants on main transmission pipelines.
Natural gas liquids are sold separately and used for enhanced oil recovery, as raw materials for oil refineries or petrochemical plants or as raw fuels.
What is hydraulic fracturing?
Hydraulic fracturing, sometimes referred to as "fracking," is the process of pumping a fluid down a well to a depth considered appropriate for natural gas production - up to 3,000 metres below the surface. The pressure this creates causes the surrounding rock to crack, or fracture. A fluid (usually water with some additives) holding a suspended proppant (usually sand) then flows into the cracks. When the pumping pressure is relieved, the water disperses leaving a thin layer of the sand to prop open the cracks. This allows the natural gas to escape from tight (low permeability) formations and flow to the well so that it can be recovered. The technology is carefully used and managed to minimize any environmental impact, particularly on groundwater.
Wellbores are carefully constructed to efficiently recover gas while protecting the surrounding environment, particularly drinking water. A well bore is drilled to allow a narrow pipe to be sunk deep into the ground. This pipe is surrounded in the bore hole with cement to ensure that both the pipe and the underground area it travels through are completely separated. To a depth below the water table, two or more layers of this casing are required in order to provide redundancy and protect groundwater. At the production site, deep underground and several hundred meters below the water table, the production pipe is perforated to allow the natural gas to be extracted. Horizontal drilling reduces the land footprint required to produce natural gas.
How can hydraulic fracturing cause seismic activity?
Hydraulic fracturing is a controlled process that injects pressurized fluids to the geological formations where natural gas is locked in dense rock, such as shale. The pressurized fluid is injected into deep shale rock formations and cracks the rock in order to release the natural gas trapped within the rocks. The energy released in this process can cause seismic activity. It is rarely felt on the surface and usually happens where the rock is being fractured, or 2,000 to 3,000 metres below ground.
CAPP's Guiding Principles and Operating Practices for Hydraulic Fracturing
- Guiding Principles
- Industry Collaboration
- Fracturing Fluid Additive Disclosure
- Fracturing Fluid Additive Risk Assessment and Management
- Baseline Groundwater Testing
- Wellbore Construction and Quality Assurance
- Water Sourcing, Measurement and Reuse
- Fluid Transport, Handling, Storage and Disposal
- Anomalous Induced Seismicity: Assessment, Monitoring, Mitigation and Response