Basic Drilling Concepts

How are wells drilled?

The basic principles of offshore drilling between open-water exploration (mobilize a rig in the middle of the ocean without any platforms installed) and development drilling (drilling from a rig above a platform) are about the same. Land drilling applies the same concept - only diferrence is........ it's on land ha ha.

Formation/soil/dirt/ground is drilled using a drilled bit. There are two types of bits widely used in the industry - tri cones and pdc (polycrystalline diamond compact) bits. Sizes range from 3" up to 30". I've also heard of bigger bits but they're rarely used. The typical ones used in my company's operations are 17-1/2", 12-1/4" and 8-1/2". The oil field is famous for the use of fractions. I guess the old foggies thought it'd be cool or something. You sometimes wonder if a tubing has an OD (outer diameter) of 2-7/8", why don't they just make it as 3" and stardardize it? God knows.


The bits are driven into formation with the use of drill pipes. Drill pipes come in an assortment of sizes but 5-1/2" DPs is the typical size. Drill pipes come in lengths of roughly 30' per joint. Wells nowadays are drilled beyond the 10km mark - especially operational areas such as Sakhalin, Russia. So imagine how many DPs are needed to reach the objectives!

The major companies supplying bits are Baker Hughes Christensen (Baker Hughes was founded by Howard Hughes' dad. Howard was the main character in the movie 'The Aviator'), Reed Hycalog and Smith International.

This is a picture taken from the drill floor looking up the derrick. The derrick on a rig hangs what's called a 'top drive' and stores drill pipes in 'stands'. A stand is 3 joints of DPs made up and racked back in the derrick. A top drive is the heart and soul of drilling - this equipment provides the rotation needed and the hoisting capability of the pipes in the well.

Let's do some quick math - Say the DP weighs 21.9 pounds per foot and imagine we're drilling a 5,000 m well. The amount of steel in the well when we reach the objective will be 21.9 x 5000 x 3.281 ft/m = 360,000 lbs. that's a lot of weight! Top drives these days are rated more than 1,000,000 lbs. They act like cranes if you will.That's the monster top drive - rated to 1M lbs of weight, up to 180 rpm rotational speed, 40,000 ft-lbs of torque. I think it's a Varco TDS4.