Page 304 - Introduction to Petroleum Engineering

THE MIDSTREAM SECTOR 293

FIguRE 15.2 Gas compressor. (Source: © energy.fanchi.com (2015).)

water can drop out of the gas phase and form a separate water phase that affects gas
flow along the pipeline. Pistonlike scrubbing devices called “pigs” are run through
pipelines to displace liquid phases to exit points along the pipeline route. Pipeline
pigs are driven by the flow of fluids in the pipeline. They remove unwanted debris
such as water and residual wax inside the pipeline. Intelligent pigs contain sensors
that can be used to inspect the internal pipeline walls and identify possible problems
such as corrosion.
Pipelines often pass through multiple jurisdictions. The route may be within a
nation or cross‐national borders. This introduces a geopolitical component to mid-
stream operations. It can also require security in regions of political instability.
The Henry Hub is an interstate pipeline interchange that is located in Vermilion
Parish, Louisiana, in the United States. The interchange is the delivery point for some
natural gas sales contracts. The price of gas in these contracts is based on the Henry
Hub benchmark price.
Other oil and gas transportation modes include trucks, trains, barges, and tankers.
Trucking is the most versatile form of transportation on land because trucks can
travel to virtually any land‐based destination. Transportation by rail can be a cost‐
effective and efficient mode of transporting large volumes of oil. Barges and tankers
transport oil and gas over bodies of water ranging from rivers to oceans.
Transportation requires moving a commodity from one point to another. It is often
necessary to provide facilities that gather and store fluids at the upstream site and
provide storage facilities at the downstream site. This requires gathering and
processing operations, as well as terminal developers and operators. Gathering lines
are smaller diameter pipelines that connect wells to larger diameter trunk lines. Large
volumes of gas and oil can be stored in spherical and cylindrical storage tanks, salt
caverns, and depleted reservoirs.
Stored gas is considered either base gas or working gas. Base gas is the amount of
gas that remains in the storage facility to maintain a safe operating pressure. Working