Raw natural gas may also contain non-energy components such as nitrogen, carbon dioxide, hydrogen sulphide and water. Most NGL s, and all the non-energy components, are removed in processing plants before the natural gas is marketable and placed into pipelines. Natural gas from coal NGC , also known as coalbed methane CBM , is an almost pure form of natural gas methane found within underground coal deposits.
The methane is contained within, and produced from, coal seams. This contrasts with conventional natural gas, which is produced from sandstones and carbonates.
Natural gas is a fossil fuel formed over millions of years from decaying plant and animal matter buried in sedimentary rock layers. Heat and pressure transform plants and animals into solid, liquid or gaseous hydrocarbons. Natural gas is contained in the pores and fractures of sedimentary rock deep beneath the surface of the earth and ocean floors. The portion of a sedimentary rock layer or a formation that contains natural gas is often referred to as a reservoir, field or pool.
Natural gas can be found throughout the world either by itself or in association with crude oil. Natural gas can be trapped in different types of sedimentary rock, including sandstone, carbonate, coal seams and shale beds. Natural gas reserves are estimated quantities of gas in known drilled reservoirs, which are near existing pipelines and markets.
These gas volumes are known with considerable certainty to be recoverable today and in future years under existing technological and economic conditions. Resources are estimated volumes of natural gas — discovered or undiscovered — that exist in subsurface accumulations. Discovered resources are estimated quantities of gas in known drilled reservoirs, which are too remote to be connected to existing pipelines and markets. If pipelines were built, gas volumes would be recoverable under existing technological and economic conditions.
Undiscovered resources are an estimate, inferred from geological data, of gas volumes thought to be recoverable under current or anticipated economic and technological conditions, but not yet discovered by drilling. These resources may be near or remote from pipelines. Before natural gas is ever drilled for and produced, geologists and geophysicists identify drilling targets where natural gas might be present.
Geologists map the subsurface by first mapping the surface exposure of formations and projecting their continuation below surface, and by using the known location of formations in drilled wells to map at depth between wells. Seismic surveys are also used to image the subsurface and help determine appropriate places to drill.
Once a drilling target is chosen, a well is drilled to the depth where natural gas is thought to exist using a drilling rig. Vertical or straight line drilling is the process of drilling a well to reach a target that is directly underneath the point of entry. Directional or slant drilling is the process of drilling a curved well, in order to reach a point that is not directly beneath the drill site. Horizontal drilling is a form of directional drilling where the well begins vertically and is then curved at a certain depth so that the well bore travels horizontally within a target formation.
If natural gas is found, casing steel pipe is placed in the well and cement is pumped around the outside of the casing to seal the different formations off from one another. The casing is then perforated at the producing zone.
Steel production tubing is also placed inside the casing, and connected to valves and pipelines at the surface. Natural gas can then be produced through the tubing up the well. Because natural gas is present at high pressure in reservoirs, and because it expands as pressure is released, natural gas will typically flow through the perforations in the casing, into the tubing, and rise up to the surface unaided by compressors or pumps. Once at the surface, the natural gas must be processed to remove water and impurities.
Raw natural gas from wells consists mostly of methane but may also contain NGL s and impurities. NGL s are separated from the natural gas either at processing facilities near the natural gas field or at straddle plants located on pipeline systems. Convert energy of gigajoule GJ and cubic feet of natural gas cu ft N.
With this energy units pair converter , a difference between two energy units are calculated to work out their corresponding equivalent values. First unit: gigajoule GJ is used for measuring energy. Second: cubic foot of natural gas cu ft N. Abbreviation, or prefix, for gigajoule is: GJ Abbreviation for cubic foot of natural gas is: cu ft N.
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