TREATMENT OF OIL AFTER LEAVING WELLS The handling of oil after it leaves the well deserves special consideration.
Such oil contains sediment and water, usually called B. S. (basic sediment). This basic sediment may comprise 4 or 5 per cent of sand. This is true in California and the Gulf Coast areas where great quantities of sand make up the sediment.
The oil in those fields is first run into settling reservoirs or sump holes at the well. The sand settles to the bottom of the hole and the oil is pumped off. Such a method is costly, as a portion of the volatile hydrocarbons escapes and leaves a heavier oil. Re cent California practice consists in running the oil through a sand box which has a riffle-like arrangement. Most of the sand settles in the box and is shoveled out from time to time by the pumper. The oil runs into a small tank where the remaining sand settles. The oil is pumped from this tank into a storage tank. Every few weeks the small tank is cleaned.
Gauging of Oil in Tanks.—Oil is bought and sold on the basis of price per barrel. The price is roughly based on the specific gravity of the oil: the light oils bring the highest prices, generally speaking, though the refining values are the final factors in deter mining price. However, the measurement of the oil in the field or in the storage tanks is made for the purpose of determining the quality and the quantity of the oil bought or sold.
The big pipe line or purchasing companies maintain gaugers at monthly salaries ranging from $150 to $300. It is the duty of these men to gauge the storage tanks on properties where the company has purchased oil, before running the oil into the pipe line. The gauger takes his measurements using a steel tape with with a plumb bob on the bottom.
The tanks are gauged both before the oil is pumped, and immediately afterward. The difference between the two read ings gives the total amount of oil run. The tanks have previously been strapped or standardized, and each inch is given a value in barrels for that tank. Once the number of inches is known the
amount of oil is readily computed. However, the temperature at which the oil is gauged causes some variation in quantity. Oil contracts with cold and expands with heat, so a standard gauging temperature of 60 ° is accepted. All readings must then be corrected for that temperature.
Again oil often contains basic sediment and water, so allowance must be made for that. This is ascertained by taking samples of the oil and.making tests with a centrifugal machine.
Samples of oil are obtained by means of an oil-thief. Samples are taken, one near the bottom, one halfway up, and one at the top.
Specific gravity tests are made with the ordinary Baume spindles. Fifty c.c. of the oil is poured into test tubes filled with 50 c.c. of gasoline, then put in the centrifugal machine and whirled vigorously for several minutes. This whirling causes a separa tion of the particles of oil and water in the sediment.
One can read the amount of water and sediment on the graduated test tube, and, dividing this by 2, obtain the full percentage of each constituent.
After accepting a tank, if not run at once, the gauger padlocks the valve gates, for cases of robbing oil tanks are known. Also unscrupulous operators might divert part of their oil to other miller tanks, and then pump it back into the larger tanks and sell it again.
of Oil and oil and water are together, as often happens, the water may, or may not, form an emulsion with the oil.
An emulsion of oil and water is an intimate mixture of oil and water in such a manner that the oil and water will not separate when allowed to settle, but form a liver-colored mixture that has the properties of neither oil nor water.
Where the water and oil do not mix, simple settling may suffice to separate the oil and the water. However, where an emulsified condition exists, heating may cause separation, or it may be nec essary to use electricity, or centrifuge, or both.