How is natural gas produced?

Completing a well

The first step in completing a gas well is to install casing, tubular steel pipe that lines the hole to prevent water and rock from entering the wellbore and ensures control of the production. The casing is sealed against the side of the well by cement pumped down the inside of the casing and up the outside, between the casing and the wellbore. Production tubing is then hung inside the casing and kept in place by inflatable rubber packers. The production tubing is connected to the wellhead, a device that contains valves and chokes which control production rates.

The next step in completing a gas well is to perforate the casing so gas can flow into the production tubing. This is accomplished by lowering a perforating gun, a device with many explosive charges that fire metal rods through the casing and into the producing reservoir.

Gas reservoirs are usually under sufficient pressure to flow to surface. Where the wellhead pressure is less than pipeline pressure, compression may be required to increase the wellhead pressure.

Some wells may require stimulation either as part of the completion process or later on in the life of the well. Stimulation includes two processes. In acidizing a well, acids, such as hydrochloric acid in carbonate reservoirs and hydrofluoric acid in sandstone reservoirs, are pumped into the producing reservoir under pressure to dissolve reservoir rock and increase the number and size of channels carrying gas to the wellbore. Another type of stimulation is fracturing, where fluids such as water or carbon dioxide are pumped into the reservoir at sufficient pressure to fracture the rock. To prevent the fractures from closing, proppant is then introduced into the reservoir. Proppant comprises sand, ceramic beads or resin coated material that acts to prop open the new fractures and enhance gas flow to the wellbore.

Developing a natural gas field

Generally, more than one well is required to produce the recoverable gas from a reservoir. Gas wells in Canada are regularly spaced to conserve resources. In Alberta, the spacing is one gas well per section with the well drilled in the centre of the section. A section of land is roughly 256 acres.

Once the gas is brought to the surface, gathering systems bring it from individual wells to processing plants. Processed natural gas consists almost entirely of methane; however, natural gas in its unprocessed state consists of methane; NGLs such as ethane, propane and butane; pentanes, water, hydrogen sulphide and other gases such as carbon dioxide and nitrogen. Most of these components are removed from the natural gas either at processing facilities at the gas field or at straddle plants located on pipeline systems. The hydrogen sulphide is extracted in the form of elemental sulphur and is used in the manufacture of fertilizers and other products. The NGLs are sold separately for use as diluent in heavy oil processing, as feedstock for petrochemical plants or as fuel.

How is natural gas transported?

Approximately 95 per cent of Canada’s crude oil and natural gas is transported by pipeline. Canada’s pipeline network totals approximately 540,000 kilometres and comprises everything from thin plastic gathering lines to steel conduits more than one metre in diameter. In gas pipelines, pumps compress the natural gas up to 100 times atmospheric pressure to move the gas at speeds up to 40 kilometres per hour. Gas is carried from producing areas in British Columbia, Alberta and Saskatchewan to distribution systems throughout Canada and the United States. As well, pipelines on the east coast of Canada carry gas from offshore reservoirs to consumers in the Maritimes and northeast United States.