Blowout Control

Hydrocarbon accumulations are becoming more and more difficult to find, and oilmen are drilling deeper and deeper in search for them. In some oilfields the pay zones are about four miles deep. At that depth pressures are extremely high, so there is always the risk of a blowout. A well, which blows out is known as a wild well and forms a gusher.

To prevent a well from blowing out, the mud weight is carefully controlled. The most common material for weighting a drilling fluid is ground barite.

If the bit suddenly enters a high-pressure formation, the weight of the mud column may not be great enough to hold back the pressure of the gas, oil or water in the borehole. Then, there will be a kick; and if the BOP rams cannot be closed quickly enough, the well will blow out. The flow must be then brought under control, so that heavy mud can be pumped to the well through the kill line. In the case of a gas-well blowout, it may be necessary first to divert the gas into a flare pit. The gas is set ablaze in the flare pit in order to prevent an explosion.

Logging the well can provide information, which may help to avoid dangerous situations down hole. Before the logging tools can be run in, the hole must be clean. If there are any tight spots, for example, it may be necessary to make a dummy trip before the drill string is pulled out. In a dummy trip the string is hoisted only a quarter or a third of the way up. Then it is run back to bottom again. In this way the bottom-hole assembly can be used to clean up the well and prepare it for logging.

Notes:

Wild well - неуправляемая скважина;

Kill line - линия глушения;

Flare pit - факельный амбар;

Dummy trip - «холостой» подъем-спуск

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