Explain Natural Gas Processing, Transmission and Storage

Natural gas primarily consists of methane, mixed with up to 20% of other gasses such as ethane and other higher order hydrocarbons. Before natural gas can be used as a fuel, it must be processed in order to remove almost all of the other impurity gasses. This process can create by-products such as butane, propane and sometimes helium and oxygen.

Natural gas may be found either in association with oil fields or in non-associated fields of natural gas alone. The decomposition of natural materials can also produce methane that is the primary gas in natural gas. Some waste treatment sites and landfills extract the methane from decomposition as a minor source of natural gas. A relatively new source of natural gas is from shale. The shale contains natural gas trapped in its geologic matrix. High pressure water and chemicals are used to break up the shale and then the gas is extracted. This source has drawn fire recently as being very polluting in its secondary effects on the environment.

Processing Plants

Processing of natural gas begins at the well heads. Water and condensate are removed before transport to a processing facility. At the processing facility a variety of chemical processes, filters and heating and cooling treatments are utilized to separate the pure natural gas from its impurities.  Major impurities removed are sulfur and mercury. At the end of the process, other impurities such as propane and benzene are also recovered and stored for commercial usage.

Transporting Natural Gas

Transmission of natural gas poses a challenge because of the low density of the gas. With this in mind, pipelines to carry natural gas are limited to distance of approximately 2500 miles on land and half of that underwater. It has been noted in the United States that the current natural gas pipelines are almost at full capacity and that demand continues to increase.

The two common methods of long distance transport are compressed natural gas (CNG) and liquefied natural gas (LNG). Liquefied natural gas carrier ships are the preferred method of cross ocean transport of natural gas. The natural gas is liquefied at its departure point and can then be returned to its natural state at the terminal or loaded into LNG trucks for further delivery.

Compressed natural gas equipment requires less capital investment and is more economical in small applications, so CNG may be used in smaller delivery operations for reasons of cost. Both LNG and CNG trucks may deliver their cargos to the end users or to a pipeline for distribution to commercial and industry users.

Storage of Natural Gas

Natural gas can be stored in depleted gas reservoirs, aquifer reservoirs or salt domes. Depleted gas reservoirs are typically the cheapest to operate but only allow for 1 cycle of injection and 1 cycle of withdrawal per year. Aquifer reservoirs require a large amount of initial investment and development and waste the most gas. They are therefore the most undesirable type of storage location. Salt formations make excellent storage facilities as the salt matrix prevents gas escape and allow multiple injection and withdrawal cycles yearly. They require more capital investment than depleted gas fields but are much more flexible.

Liquid natural gas may be stored indefinitely in underground storage tanks. Due to the compressed liquid nature of the gas, six hundred times more gas may be stored in liquid form in the same space as gas in its natural form. LNG is also easy to transport on short notice to consumers. The primary disadvantage is the expense of constructing and maintaining the LNG storage facility.

Natural gas is a popular choice for heating and electrical generation needs because of its lesser impact on the environment than other fossil fuels such as oil and kerosene. It is still a significant source of greenhouse gasses and, as with oil, is a finite resource subject to price and supply fluctuations. These concerns of price and supply volatility are a large factor for nation states in formulating their national policies regarding processing, transportation and storage of natural gas.