BOP

Semi-submersible rigs are often referred to as semis , and are a floating type of rig. Like the jack-up, a semi is self contained. The structure is supported by large pontoons which are ballasted with water to provide the required stability and height. The rig is held in position by anchors and mooring lines or dynamically positioned by thrusters. A large diameter steel pipe ( riser ) is connected to the sea-bed and serves as a conduit for the drill string. The blowout preventer (BOP) is also located at the sea-bed ( sub sea stack ). 

An important safety feature on every modern rig is the blowout preventer (BOP). As discussed earlier on, one of the purposes of the drilling mud is to provide a hydrostatic head of fluid to counterbalance the pore pressure of fluids in permeable formations. However, for a variety of reasons (see section 3.6 Drilling Problems ) the well may kick , i.e. formation fluids may enter the wellbore, upsetting the balance of the system, pushing mud out of the hole, and exposing the upper part of the hole and equipment to the higher pressures of the deep subsurface. If left uncontrolled, this can lead to a blowout, a situation where formation fluids flow to the surface in an uncontrolled manner. 

In the event of a sudden loss of mud In an Interval containing overpressures the mud column in the annulus will drop, thereby reducing the hydrostatic head acting on the formation to the point where formation pressure exceeds mud pressure. Formation fluids (oil, gas or water) can now enter the borehole and travel upwards. In the process the gas will expand considerably but will maintain its initial pressure. The last line of defence leff is the blowout preventer. However, although the BOP will prevent fluid or gas escape to the surface, closing in the well may lead to two potentially disastrous situations ... 

If a situation arises whereby formation fluid or gas enters the bore bole the driller will notice an increase in the total volume of mud. Other indications such as a sudden increase in penetration rate and a decrease in pump pressure may also indicate an influx. Much depends on a quick response of the driller to close in the well before substantial volumes of formation fluid have entered the borehole. Onoe the BOP is closed, the new mud gradient required to restore balance to the system can be calculated. The heavier mud is then circulated in through the kill line and the lighter mud and influx is circulated out through the choke line. Once overbalance is restored, the BOP can be opened again and drilling operations continue. 

In oxygen steelmaking, 99.5% pure oxygen gas is mixed with hot metal, causiag the oxidation of the excess carbon and siHcon ia the hot metal and thereby produciag steel. In the United States, this process is called the basic-oxygen process (BOP) (4,9,10). The first U.S. commercial iastallation began operation in 1955. 

Fig. 6. Liquid blast-fiimace iron (hot metal) being charged into a 200-metric ton Q-BOP furnace in preparation for making a heat of steel.

RCO2H, R OH, BOP-Cl, Et3N, CH2CI2, 23°, 2 h, 71-99% yield. This is an excellent general method for the preparation of esters. 

Phenyl esters can be prepared from A-protected amino acids (PhOH, DCC, CH2CI2, -20° 20°, 12 h, 86% yield PhOH, BOP, Et3N, CH2CI2, 25°, 2 h. 

Benzotriazol-l-yloxytris(dimethylamino)phosphonium hexafluorophosphate (BOP reagent)... 

Phenyl esters can be prepared from A-protected amino acids (PhOH, DCC, CH2CI2, -20° 20°, 12 h, 86% yield PhOH, BOP, Et.N, CH2CI2, 25°, 2 h, 73-97% yield ). Phenyl esters are readily cleaved under basic conditions (H2O2, H2O, DMF, pH 10.5, 20°, 15 min). ... 

BOP.benzotriazol-1 -yloxy-tris(dimethylamino)-phosphonium hexafluorophosphate... 

Figure 4-188. BOP stack arrangment for high cellar rigs.

This rather complicated procedure has been necessary because the drilling rig can only accommodate the BOP stack that has only one set of pipe rams and a blind ram (i.e.. Figure 4-188). It is obvious if the rig could accommodate the taller BOP stack with two pipe rams (namely Figure 4-187), one pipe ram could be for 3 in. drill pipe and the other for the 4 in. liner. Such an arrangement would greatly simplify the safety procedures necessary for placing the 4 in. liner into the borehole. 

A formation fluid kick can be efficiently and safely controlled if the proper equipment is installed at the surface. One of several possible arrangements of pressure control equipment is shown in Figure 4-351. The blowout preventer (BOP) consists of a spherical preventer (Hydril), blind and pipe rams, and the drilling spool. 

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