[PART 1]

BY JIM-REXLAWSON MOSES

Rotary drilling is used in almost all oil and gas wells drilled globally. In this method of drilling, a length of steel pipe- with a drill bit on the end is rotated to cut a hole called the well bore. As the drilling goes deeper, additional sections of drillpipe are added to the top of the rotating drill string.

Rotary drilling uses a steel tower to support the drillpipe. If the tower is part of a tractor-trailer and is jacked up as a unit, it is called a mast. If it is constructed on site, it is called a derrick. Both towers are constructed of structural steel and sit on a flat steel surface called the drill or derrick floor; this is where most of the drilling activity occurs. Four major systems comprise an operational rotary drilling rig: the power supply, the hoisting system, the rotating system, and the circulating system.

An operational rig requires a dependable power supply in order for the other rig systems to operate. Power to these systems may be supplied through one or more diesel engines used alone or in conjunction with an electrical power supply.

The hoisting system raises, lowers, and suspends equipment in the well and typically consists of a drilling or hoisting line composed of wound steel cable spooled over a revolving reel. The cable passes through a number of pulleys, including one suspended from the top of thederrick or mast. The hoisting system is used to move drillpipe into or out of the well.

The rotating system includes the turning drill pipe, the drill bit, and related equipment. It cuts the well bore, which may have an initial diameter of 20 in. (51 cm) or more but is usually less.

The drill bit is located at the bottom end of the first drill pipe within the rotating system. The drill pipe is rotated by a rotary table located on the derrick floor. The drillpipe consists of heattreated alloy steel and may range in length from 18 to 45 ft (5 to 14 m); drill pipe length is typically uniform at each individual drilling rig. Before the drill pipe is fully inserted into the well bore, another section of drillpipe is added.

During drilling, the circulating system pumps drilling mud or fluids into the well bore to Cool the drill bit, remove rock chips, and control subsurface fluids. Typically, mud is circulateddown through the hollow drillpipe. The mud exits the pipe through holes or nozzles in the drill bit, and returns to the surface through the space between the drillpipe and the well bore wall.

Drilling muds (also termed fluids) are used during the drilling process to transport rock cuttings from the bottom of the well up and out of the well bore, where the cuttings are screened and removed, and the separated mud is reused. Drilling muds also act to cool the drill bit, to stabilize the well walls during drilling, and to control formation fluids that may flow into the well.

The most common drilling mud is a liquid-based mud typically composed of a base fluid(such as water, diesel oil, mineral oil, or a synthetic compound), with optional additives such as weighting agents (most commonly barium sulfate), bentonite clay (to help remove cuttings and to form a filler cake on the well bore walls), and lignosulfates and lignites (to keep the mud in a fluid state).

Blowout Preventer

No drilling site can operate without a blowout preventer. The blowout preventer, which is routinely used in onshore and offshore drilling, prevents oil, gas, and/or other subsurface liquids (i.e., salt water) from leaving the well and escaping into the environment.

Drilling for oil offshore still poses a threat to our environment; therefore, every modern oil rig has safety procedures and equipment as a failsafe in the event an accident occurs that could cause an explosion and/or oil spill.

Oil rig blow outs occur when underground pressure is encountered and there is no quick way to displace the pressure. or fluid will force its way to the surface and will cause an overwhelming release of pressure, which may lead to an explosion, fire, loss of life, oil spill and/or damage to the rig.

A blowout preventer, or BOP, is a failsafe valve mechanism to prevent explosions and/or oil spillage. Rig operators always feel a little safer knowing that in an emergency, the blowout preventer’s giant hydraulic pistons and shears would clamp shut a gushing well.

At the bottom of a well, there are two fluid pressures. Pressure on fluids in the formation tries to force the fluids to flow from the formation into the well. Pressure exerted by the weight of the drilling mud filling the well tries to force the drilling mud into the surrounding rocks.

Under normal operations, the effective weight of the drilling mud is adjusted to exert a slightly greater pressure on the bottom of the well than the effective pressure on the fluid in the rocks, causing the mud to enter the rock and cover the sides of the well and thus stabilize the well.

If the pressure on the fluid in the rocks is greater than the pressure of the drilling mud, water, gas , or oil will flow out of the rock into the well. In extreme cases, a blowout occurs where the fluids flow uncontrolled into the well and on occasion violently to the surface.

A blowout preventer is a device that is used to close off a well if there is a loss of control of the fluids in the formation. There are a variety of types of blowout preventers. Some close over the top of the well bore, some are designed to seal around the tubular components in the well (such as the drillpipe, casing, or tubing), and some have hardened steel shearing surfaces that actually cut through the drill pipe to seal off the opening.