Get to know the drilling industry

Drilling for oil and gas, often far out at sea in waters several kilometres deep, is a remarkable feat of human tenacity and technological ingenuity. Find out more about how a drilling company locates and drills for oil or gas, using rigs, semi-submersibles and drillships.

Drilling into reservoirs of fossil fuels is a concept that dates back to the 19th century – but it has always been hugely difficult to achieve successfully in practice. Today Maersk Drilling is one of the world’s leading drilling companies, pioneering new solutions to tough challenges.

Drilling rig types

Jack-ups

Semi-submersibles

Drillships

The phases of drilling

The drilling process begins when geologists from an oil company identify a potential oil or gas reservoir. Drilling rights are then obtained to the site to prepare it for exploratory drilling.

Phase 1: Exploration

Maersk Drilling sends a mobile drilling rig to the site to drill the initial exploration well that includes taking a core sample, which geologists analyse for signs of oil or gas. The drilling rig will typically drill several exploration wells to obtain the data required for development, each taking a few months to complete. A positive find (called ‘a show’) is followed by more exploratory wells to verify the quality before taking the next step: drilling the much more elaborate development/production wells.

Phase 2: Drilling begins

A drill bit is attached to a ‘drill string’ made of bottom hole assembly and drill pipe. The drill bit is lowered to the seabed – sometimes to a depth of several kilometres – until drilling is ready to commence. The drill is rotated by a top drive on the rig floor, and as the drill string is lowered, it cuts away the rock. The hole can be drilled vertically, at an angle or eve horizontally. Lengths of drill pipe are added on the rig floor to extend the process till the required depth is reached.

For cooling, cleaning and stabilising pressure, a ‘drilling fluid’ is pumped through the drill pipe and out through nozzles in the drill bit at high velocity. The fluid is usually a mixture of water, clay, barite and chemicals - known as drilling mud. Back on the rig, the fluid is continuously recycled through a closed circulation system that disperses the drilled rock and recycles the drilling mud.

Phase 3: Finalising the well

When the drill bit reaches target depth, production casing and completion tubing is lowered into the well and cemented into place. The well is then brought online allowing oil or gas to flow to surface for testing, so the reservoir can be verified for its size.

Once the above process is complete the drilling rig will suspend the well and move away. In time a production platform or subsea structure will be put in place. An average well can last decades, so offshore production platforms and subsea structures are built to produce and last many years.