How Oil Wells Are Drilled and Drilling Rigs

The process by which an oil or gas well is drilled has changed little in the last hundred years. The technology and equipment though have become much more complex.

Hard working men and sometimes women, known as roughnecks toil away in every type of weather condition as a drill bit bores down through layers of earth and rock to a zone below that contains oil.

Although the basic procedure has changed little the equipment and technology has.

A drilling rig consists of a large superstructure that is placed over the spot where the well will be drilled. This can be a land type rig or offshore platform or jackup rig, even a drill ship.

A large derrick sits on top of this superstructure. The derrick allows long lengths of pipe or combined pipe (stands) to be raised in and out of the well.

At the top of the derrick is the crown, where the large pulleys and drill line or cable are are ran from down below.

These cables or drill line raise and lower the blocks, which are like a large block and tackle that can hold the weight of the heavy drill pipe.

There are a couple of ways that the rig an turn the drill pipe to drill the hole. One is with a rotary table. The rotary table is powered by a diesel or diesel electric motor at the base of the rig.

A hexagonal length of pipe called the kelly fits in a similar shaped slot which the rotary table turns.

The kelly is attached to a length of drill pipe and as it is turned and the drill pipe bores into the ground another and another is added until the desired depth is reached.

Another method does not use a kelly or rotary table but instead a motor mounted up in the derrick called a top drive.

With a top drive there is no need to attach a kelly and therefore longer lengths of combined pipe (stands), as many as ninety feet or more an be drilled down at once.

Because fewer connections need to be made the drilling process is speeded up and wells can be completed faster. This method is suited to places where the ROP or rate of penetration is fast.

Modern drilling rigs use drilling fluid or mud that is made of bentonite, barite and other minerals combined with water , diesel or synthetic ingredients.

The drilling fluid or mud lubricates the bit, flushes cuttings from the well and helps control high underground pressures.

For more on how oil and gas wells are drilled and for a complete listing of oil and gas drilling books such as "A Nontechnical Guide To Oil Well Drilling" try the Oilfield Bookstore at the link below.