What worker doing during Drilling Operation?

During drilling, the personnel and equipment must be protected against unexpected pressure surges in the wellbore. In oil and gas drilling, these surges can come from hydrocarbon fluids trapped under impermeable rock which holds them at pressures higher than the static head of the fluid column in the wellbore, and in geothermal operations the surges come from hot formations which heat the pore or wellbore fluids above the saturation temperature at the static wellbore pressure. In either case, the first line of control is the weight of the fluid column in the wellbore. 

With a gas column, this weight is negligible, but with mud the liquid density will range from slightly greater than water (-8.5 pounds per gallon) to almost three times that. In addition to the clays and additives which raise the viscosity of the mud to improve hole cleaning, weighting materials such as barite are often added to increase the mud's density and enable it to control higher downhole pressures.

The pressure surge cannot immediately be controlled with fluid weight, the wellbore can be mechanically sealed at the surface with BOPS, or blow-out preventers. There are three principal types of BOP: blind rams, which are sliding plates that come together across the wellbore when the drill string is not in the hole; pipe rams, which are like blind rams except that the sliding plates are cut out in the center so the rams can seal around the drill pipe; and an annular preventer, which is an inflatable bladder that seals around drill collars, stabilizers, or other off-size or irregularly shaped tools.

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Classification of BOP - Blowout Preventer

There are several types of BOPs, as they can be classified according to their scope, and their conformation.

Classification for use:

The first subdivision distinguishes the onshore (offshore) BOPs . The first ones are generally smaller and simpler, and are used exclusively in drilling rigs on the mainland. Submarines BOPs, on the other hand, are designed to operate in offshore fields, and therefore are used in oil platforms or drillships . They have a more advanced technology, especially for what concerns the control mode of the BOP itself having to be activated from remote locations, and are also more impressive, because of the presence of a frame (chassis) of support, and the different conformation of the wells submarines.

The split of a Blowout preventer stack: the upper one is an annular BOP, the lower one represents a BOP on a jaw.

Classification by constructive technology :

The classification as a function of their architecture, distinguishes between the so-called BOP - blowout preventer

The first ones consist of a rubber ring, perforated in the center and whose hole diameter is equal to that of the well. The ring is contained in a steel crankcase . Inside the crankcase , and under the rubber ring, a hydraulic piston is mounted , which when actuated compresses or decompresses the ring from bottom to top or from top to bottom. In this way the ring (also called anular ) is closed or opened.

The jaws BOPs are also made of a metal casing, in which there are two opposing jaws, and may differ in "Combi", that is, with jaws coupled to two to two in two arms, or "Quad", with four distinct arms.

In the case of BOP for Coiled Tubing of Quad type, we find the following rams: Top Blind Rams, which have the function of hermetically closing the shaft; Shear Rams or Cutter Rams, which have the task of cutting the coiled tubing that is well with blades, followed by the Rams Slip, which have the shape of wedges, which have the task of supporting the coiled tube section cut and left in well. Finally there are the Rams Pipe that must ensure hydraulic seal on the tube and prevent the shaft pressure from creating a Blowout.

Between the Cutters and the Slip there is a kill line, a point where fluid can be pumped to "kill" the well, that is to provide a hydrostatic to the latter, which avoids the blowout. The jaws are controlled by hydraulic pistons through which they can be closed or opened. The first jawbone BOP was invented in 1922.

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What is Blow Out Preventer - BOP

The blowout preventer or BOP is a particular device used during the drilling of a hydrocarbon well that has the task of securing the well during the drilling phase, in case the underground fluids accidentally migrate to the outside of the well , during drilling.

The well can be assimilated to a circular section duct, therefore substantially to a long pipe . The hydrocarbon is contained in the porous ground pores, subjected to the formation pressure and maintained in the rock by the counter pressure exerted on the hole walls of the drilling mud .

If for any reason, these fluids, coming from the well, toward the surface, would reach the perforation plant , which is on the surface of the well mouth. In this way the plant would be seriously threatened by the risk of fires and explosions , just because the gas is easily flammable . Among other things, such gases, rising upwards, expand because it decreases the hydrostatic pressure to which they are subjected. This would mean that the whole plant would be wrapped in flammable gas, ready to light up to the minimum spark or hot surface contact. Even if the gases do not get burned, they would cause respiratory or asphyxiating problems as wellpersonal poisoning .

The BOP is therefore used to close the shaft in emergency situations, ie blocking its section in case of blowout , that is, the shaft eruption (so is called the hydrocarbon spill from it).

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