The oil and gas industry is divided into three major components: upstream, midstream, and downstream. The midstream sector consists of transportation, storage, and distribution of oil and gas products. The means of transportation are by pipeline, rail, barge or truck in order to transfer crude oil from upstream production sites to downstream facilities such as refineries and petrochemical plants.
Midstream operations and processes include the following:
Gathering – utilizes narrow low-pressure pipelines to connect oil- and gas-producing wells to larger, long-haul pipelines or processing facilities.
Processing/Refining – turn crude oil and gas into marketable products.
Transportation – oil and gas are transported to processing facilities, and from there to end users, by pipeline, tanker/barge, truck and rail.
Storage – provide storage facilities at terminals throughout the oil and gas distribution systems.
Technological applications – apply technological solutions to improve efficiency during midstream processes. Technology can be used during compression of fuels to ease flow through pipelines; to better detect leaks in pipelines; and to automate communications for better pipeline and equipment monitoring.
The midstream facilities include gas plants, LNG production and regasification, and oil and gas pipeline systems.
Gas processing consists of separating the various hydrocarbons and fluids from the pure natural gas to produce what is known as “pipeline quality” dry natural gas. Major transportation pipelines usually impose restrictions on the makeup of natural gas that is allowed into the pipeline. Before the natural gas can be transported, it must be purified.
Whatever the source of the natural gas, once separated from crude oil (if present), it commonly exists in mixtures with other hydrocarbons, principally ethane, propane, butane and pentanes. In addition, raw natural gas contains water vapor, hydrogen sulfide (H2S), carbon dioxide, helium, nitrogen and other compounds. Associated hydrocarbons, known as “natural gas liquids” (NGL), are used as raw materials for oil refineries or petrochemical plants and as sources of energy.
Gas from a pure natural gas wellhead might have sufficient pressure to feed directly into a pipeline transport system. Gas from separators has generally lost so much pressure that it must be recompressed to be transported. Turbine-driven compressors gain their energy by using a small proportion of the natural gas that they compress. The turbine itself serves to operate a centrifugal compressor, which contains a type of fan that compresses and pumps the natural gas through the pipeline. Some compressor stations are operated by using an electric motor to turn the centrifugal compressor. This type of compression does not require the use of any natural gas from the pipe; however, it does require a reliable source of electricity nearby. The compression includes a large section of associated equipment such as scrubbers (to remove liquid droplets) and heat exchangers, lube oil treatment, etc.
Pipelines can measure anywhere from 6 to 48 inches (15-120 cm) in diameter. In order to ensure their efficient and safe operation, operators routinely inspect their pipelines for corrosion and defects. This is done with sophisticated pieces of equipment known as “pigs”. Pigs are intelligent robotic devices that are propelled down pipelines to evaluate the interior of the pipe. Pigs can test pipe thickness, roundness, check for signs of corrosion, detect minute leaks, and any other defect along the interior of the pipeline that may either restrict the flow of gas, or pose a potential safety risk for the operation of the pipeline. Sending a pig down a pipeline is fittingly known as “pigging”. The export facility must contain equipment to safely insert and retrieve pigs from the pipeline as well as depressurization, referred to as pig launchers and pig receivers.
Loading on tankers involves loading systems, ranging from tanker jetties to sophisticated single-point mooring and loading systems that allow the tanker to dock and load the product, even in bad weather.
LNG Liquefaction and Regasification Facilities
Natural gas that is mainly methane cannot be compressed to liquid state at normal ambient temperature. Except for special uses such as compressed natural gas (CNG), the only practical solution to long distance gas transportation when a pipeline is not available or economical is to produce LNG at -162 Â°C. This requires one or more cooling stages. Cooling work consumes 6-10% of the energy to be transported. Special insulated tank LNG carriers are required for transportation, and at the receiving end, a regasification terminal heats the LNG to vaporization for pipeline distribution.
The next part will be about Fractional Distillation, please stay tuned.