PNG 301
Introduction to Petroleum and Natural Gas Engineering

8.4.3: Offshore Drilling Rigs


In 2015, offshore oil production accounted for approximately 30 percent of global oil production[2]. The more prolific offshore regions of the world include the U.S. Gulf of Mexico, the North Sea, the Arabian/Persian Gulf, the Caspian Sea, offshore West Africa, amongst others. The principles of rotary drilling for offshore oil and gas are essentially the same as those of onshore drilling; however, the rigs used for offshore drilling must be placed on sea-going vessels or on fixed Production, Drilling, and Quarters platforms.

When placed on sea-going vessels, the drilling rig forms an integral component of a Mobile Offshore Drilling Unit (MODU). The MODUs discussed in this lesson are Jack-Up Rigs, Semi-Submersible Rigs, and Drill Ships. Drilling rigs on fixed Production, Drilling, and Quarters (PDQ) platforms are not mobile, and hence, not considered to be a Mobile Offshore Drilling Unit.

Before we continue with this discussion, we must make a distinction between an offshore platform and an offshore rig; they are not synonymous. An offshore oil or gas platform (or some other offshore facility such as a Floating Production Storage and Offloading (FPSO) vessel) is used for production, injection, artificial lift, fluid separation and treating, fluid export, and possibly drilling. In other words, an offshore platform is used for all operations associated with the extraction of hydrocarbons from offshore oil or gas fields. On the other hand, an offshore rig is used exclusively for drilling and workover operations.

The following pages will discuss four types of offshore drilling rigs.

  • Jack-Up Rig
  • Semi-Submersible Rig
  • Drill Ships
  • Drilling Rigs on Fixed Production Platforms

[2] U.S. Energy Information: Offshore production nearly 30% of global crude oil output in 2015