石油钻井英语

Well control

The drilling fluid that courses through the system also provides the first line of defense against blowouts. A blowout can be an impressive sight. Gas ,oil , or salt water spews into the air with tremendous roar. If gas is present , the whole thing will probably be on fire , and the rig will lie as a melted, twisted mass of junk. Human lives are threatened ; pollution may occur ; precious oil and gas are wasted ; and a rig worth many thousands or even millions of dollars may be a total loss. Obviously, it is very desirable not to allow blowouts, and , in fact, not many occur. But ,because a blowout is often a spectacular show and human lives a sometimes lost, a blowout often becomes a media event. Unfortunately, the impression may linger that blowouts are not the rarity they actually are. In reality, rig crews go to great lengths to see that the well they are drilling remains under control and control and does not get away from them.

A hole full of mud that weights the right amount, or has the proper density, will not blow out. But sometimes the unexpected occurs. Since a rig crew is only human, an error can be made and formation fluids such as gas, salt water, oil, or all three enter the hole. When a kick occurs, it make its presence known by certain things that happen in circulating system. For example, the level of mud in the pits may rise above the normal level, or mud may flow out of the well even with the pump stopped , or shut down. An alert crew can spot these anomalies (even though the anomalies are sometimes stubtle) and take action to prevent a blowout. It is here that the second line of defense against blowouts is brought into play—the blowout preventers (BOPS).

On land rigs and on offshore rigs, such as platforms and jackups that are not floats, BOPs are attached to the top of the well beneath the rig floor. The preventers are nothing more than large, high-pressure valves capable of being remotely controlled. When closed, they form a pressure-tight seal at the top of the well and prevent the escape of fluids. On floating offshore rigs, such as semisubmersibles and dill ships, the blowout preventers are attached to the well on the seafloor.

Two basic types of blowout preventers are annular and ram. The annular preventer is usually mounted at the very top of the stack of the BOPs. It is called annular because it seals off the annulus between the drill pipe or Kelly and the side of the hole. An annular BOP can also seal off an open hole—a hole no pipe in it. Below the annular preventer in the BOP stack are typically mounted to two , three, or even four ram—type BOPs. Ram preventers get their name from the fact that the devices that seal off the well are large, rubber—faced blocks of steel that are rammed together, much like a couple of fighting rams butting heads. Of the ram—type preventers there are blind rams, which seal off open hole, and pipe rams, which seal off the hole when dill pipe is in use. Usually, only the annular preventer will be closed when the well kicks, but should it fails, or should it be necessary to use special techniques, the ram—type preventers are used as a backup. Of course, closing in the well with one or more of the blowout preventers is only the first step that much be taken. In order to resume dilling, the kick must be circulated out and mud of the proper weight circulated in. therefore, a series of valves called the chock manifold is installed as part of the system. A choke is simply a valve whose opening is capable of being restricted or pinched in. it can be fully open or fully closed, and it may be infinitely variable in size between open and closed. In order to circulate the kick out of the well and pump heavy mud in, the choke is fully opened, the mud pump started, and, as the kick starts moving up the hole, the choke opening reduced in size by an amount that holds just enough back—pressure to allow the mud and kick out but prevents further entry of formation fluid. Once the kick is out and the heavier mud in, a few