What is a drillship?
Updated: Feb 25, 2022
Oil was first struck in the United States in 1859 at a depth of 69 feet underground, beginning the U.S. oil industry and oil rush. People quickly moved away from wood, coal, and steam, toward oil and natural gas, and by 1873, output was 10,000,000 barrels. Demand continued to grow rapidly as individual energy needs grew along with population growth and we started to search for oil offshore. Starting with shallow waters, technology allowed us to move farther out and now deepwater drilling is common. Today we’re going to take a look at drillships, vessels that drill for oil, gas, and coring research deep in the ocean. We’ll also take a look at some of the interesting drillships in the industry.
Mobile Offshore Drilling Units, or MODUs are drilling vessels that are capable of relocating to drill in multiple locations in the ocean. Jack-ups, semisubmersibles, and drillships all fit into this category.
“The Jack Ryan, a drill ship capable of exploring for oil in water 3,000 metres (10,000 feet) deep.” Image from Britannica.
Drillships are much more like a traditional ship than jack-ups or semi-submersibles - they have a ship shape, run under their own power, and are smaller than the other two. They also drill the deepest, as some drillships like the Chikyū are capable of drilling 7,000 meters into the sea floor. Drillships have a derrick mounted on deck with drilling equipment that passes through a moonpool in the bottom of the hull. The moonpool is a hole in the bottom of the hull that is covered during transit and uncovered for drilling, allowing drilling equipment to be mounted in the middle of the vessel and passed straight through the hull into the water. Moonpools are also common on research vessels, diving vessels, and ROV vessels to safely lower people and equipment into the sea.
Dynamic positioning is standard on drillships, which gives them great position keeping in rough waters, but they are less stable than other MODUs due to their smaller size and lack of mooring. DP systems use azimuth thrusters that rotate 360 degrees, as well as tunnel thrusters for stationkeeping at sea. DP2 or DP3 systems are standard on modern drillships, providing redundancy in systems to keep vessels on location in the case of an electrical fault or accident. DP2 vessels have the ability to stay on station with the failure of an active component and DP3 systems have the ability to stay online with the loss of an entire compartment due to flood or fire damage. Because of their shape and power, they have excellent mobility and are commonly used for exploratory wells because they can relocate quickly. They also make great research ships for retrieving core samples with plenty of room for labs and a couple hundred people and crew. They also have ample storage for supplies including lengths of pipe and drilling equipment needed to drill thousands of meters into the seafloor.
Azimuth thrusters that would be used with a dynamic positioning system. Image from Thrustmaster.
Bully drillship. Image from Upstream Online.
The trend was toward larger and larger drillships, but some companies like Shell took a different approach by making these vessels a little smaller, reducing fuel and operational costs while still getting the job done. The Bully I and Bully II were both smaller than a traditional drillship, but with the same capability as larger vessels. They worked with Huisman to design the drilling package first, and then designed the vessel around that equipment. According to Shell, the drill and well lining equipment was located outside of the tower, allowing the drilling floor to be raised to install blow out preventers, which leaves a much lower center of gravity on the vessel compared to a traditional raised drilling floor. This is an important innovation as blow out preventers often have multiple pieces the size of a small building that must be installed on the well. The Bully vessels were also about 2.5 meters narrower and up to 80 meters shorter than the largest drillships, creating a smaller package that included more automated technology to save costs and time. Bully I and Bully two are no longer in service and were sold a few years ago and contracts between Shell and Noble settled, according to Seeking Alpha.
Research drillship: Chikyū
Chikyū on the water. Image from JAMSTEC.
The Chikyū is a research vessel built to drill 7,000 meters into the seafloor to retrieve material directly from the Earth’s mantle, a task that has never been done before. Collecting samples directly from tectonic plates will help scientists understand earthquakes and how the plates move. The vessel has a normal drillship layout with a large drilling tower and a moonpool for the drilling equipment, including an automated pipe transfer system. It’s powered by six azimuth thrusters and one side thruster, allowing it to keep position in rough waters for months at a time during deep drills. The vessel carries about 100 crew and approximately 50 scientists who have a full laboratory setup, including CT and x-ray scanners, microbiology, geochemistry, and petrology labs, and more. The current record for deepest hole ever drilled in the ocean is held by the Chikyū at 3,250 meters, but the goal remains to drill to about 5,200 meters for a sample of where two tectonic plates meet. Under such depths and pressures, every new record is met with a new challenge to be solved. Check out our full article, Chikyū: World Record Drillship.
If you’d like to learn more about dynamically positioned vessels check out the articles below. OneStep Power tests DP2 and DP3 ships for fault ride through to verify systems won’t go offline in the case of a fault - important for ships that do research, drill, and install wind turbines!
Articles on other research vessels:
Happy Fun Fact Friday!