Pipelines

Pipelines provide surface transport for both gas and liquids. They are constructed by welding together joints of large-diameter steel pipe. Most pipelines are externally coated and wrapped for protection from corrosion and abrasion. Onshore pipelines are buried. Shallow-water offshore lines are usually buried for protection, but deeper-water lines may not be buried. Single-phase pipelines transport either gas or liquid, but not both. Two-phase pipelines transport both liquid and gas. In two-phase lines, liquid builds up in the low spots and then starts moving as a slug (filling the entire line). The alternating high-volume slugs of gas and liquid emerging at the end of the line make severe demands on the separation equipment.

Pipelines are used both in gathering systems- moving produced fluids between facilities within the field- and for final transport of fluids away from the field.

Rubber swabs or spheres called pigs are periodically run through pipelines to sweep out accumulated water and debris. The pigs fit tightly, forming a seal against the inside of the line so that fluid pressure propels them. They are inserted and removed from the pressurized line through a pig launcher at the beginning of the line and a pig trap at the end of the line.