RECOVERING the OIL

Sometimes when oil sand is reached, only a little oil comes out of the pipe. This may be because the porous rock has such fine holes that the oil can't seep through fast enough or it may be that the pores are clogged with lime. Now specialists are called in. First an acidizer studies the problem carefully. Then he pours down a quantity of hy­drochloric acid to dissolve the lime clogging the pores in the oil sand.

Oil Recovery

If the oil still doesn't come, a well shooter starts to work. After the lowest casing has been hauled up out of danger, he carefully lowers tin torpedoes filled with nitroglycerin to the bottom of the hole. They are set off by a time bomb, and the sandstone is blasted, opening passages through which oil can reach the pipe.

When the drill nears the limestone stratum where the driller hopes to find oil, a control head is screwed to the top casing to keep well from blowing. Sometimes when the drill pierces an oil pool, the oil and gas, under heavy pressure, roar out of the pipe. Without a control head, the drilling tools would be shot into the air and the derrick would be wrecked. In the early days of the oil industry, new wells often came in as gushers. In these wells great underground pressure forced the oil upward without any control, and it was necessary to wait until the pressure dropped enough for the oil to flow at a normal rate before any of it could be recovered. Of course, a great deal of oil was wasted when a well gushed in this way.

Oilmen used to cheer gushers as a sinn of oil, but feared them also, for sometimes thousands of barrels of oil were lost or took fire before a well could be brought under control.

Chapter Four

At the top of the head is a strange object called a Christmas tree. This is a maze of pipes and valves which leads the oil from the well pipe to the tanks scattered about the wellhead and controls the gush­er and the amount of oil which is allowed to flow to the surface.

Each pipe of a Christmas tree is fitted with a control valve. If the flow is light, only a few valves are opened; with more pressure, more valves are turned on, and if the oil roars up under heavy pressure all the pipes are opened, and the oil is allowed to flow to every tank on the lot. The Christmas tree prevents oil from being wasted through overflow. Also, because it controls the amount of oil allowed to es-

Oil Recovery

exercise

cape from the pool underground, it keeps the pressure steady in the oil reservoir.

Every oil reservoir contains more or less gas dissolved in it; this gas keeps the oil light and easy-flowing. If pressure is reduced too much, part of the gas separates from the oil end escapes through the pipe. Then the oil becomes so heavy that it won't flow. The driller regulates the flow by opening or closing the valves on the Christmas tree. If he lets oil into the tanks too rapidly, the pressure in the pool goes down faster than it can be built up by the water pressure around it. Oil does not really flow rapidly through sand or rock: it must be forced to move. With less pressure and heavier oil it is necessary to use pumps to force the oil up the pipe. Sometimes even pumping can't bring it up. Then the well is abandoned.