Offshore Drilling (Natural Oil & Gas)

Drilling for natural gas offshore, in some instances hundreds of miles away from the nearest landmass, poses a number of different challenges over drilling onshore. The actual drilling mechanism used to delve into the sea floor is much the same as can be found on an onshore rig. However, with drilling at sea, the sea floor can sometimes be thousands of feet below sea level. Therefore, while with onshore drilling the ground provides a platform from which to drill, at sea an artificial drilling platform must be constructed.



Drilling offshore dates back as early as 1869, when one of the first patents was granted to T.F. Rowland for his offshore drilling rig design. This rig was designed to operate in very shallow water, but the anchored four legged tower bears much resemblance to modern offshore rigs. It wasn't until after World War II that the first offshore well, completely out of sight from land, was drilled in the Gulf of Mexico in 1947. Since then, offshore production, particularly in the Gulf of Mexico, has been very successful, with the discovery and delivery of a great number of large oil and gas deposits. Learn about offshore drilling statistics, including the number of wells being drilled and their productivity. Learn about the environmental effects of drilling for petroleum offshore.

The Drilling Template

Since the land that is going to be drilled through cannot provide a base for offshore drilling as it does for onshore drilling, an artificial platform must be created. This artificial platform can take many forms, depending on the characteristics of the well to be drilled, including how far underwater the drilling target is. One of the most important pieces of equipment for offshore drilling is the subsea drilling template. Essentially, this piece of equipment connects the underwater well site to the drilling platform on the surface of the water. This device, resembling a cookie cutter, consists of an open steel box with multiple holes in it, dependent on the number of wells to be drilled. This drilling template is placed over the well site, usually lowered into the exact position required using satellite and GPS technology. A relatively shallow hole is then dug, in which the drilling template is cemented into place. The drilling template, secured to the sea floor and attached to the drilling platform above with cables, allows for accurate drilling to take place, but allows for the movement of the platform above, which will inevitably be affected by shifting wind and water currents.

In addition to the drilling template, a blowout preventer is installed on the sea floor. This system, much the same as that used in onshore drilling, prevents any oil or gas from seeping out into the water. Above the blowout preventer, a specialized system known as a 'marine riser' extends from the sea floor to the drilling platform above. The marine riser is designed to house the drill bit and drillstring, and yet be flexible enough to deal with the movement of the drilling platform. Strategically placed slip and ball joints in the marine riser allow the subsea well to be unaffected by the pitching and rolling of the drilling platform.