of oil to 100'cc. of fluid. The limit of water and base sediment is usually 3% and anything in excess of that figure is rejected. The temperature and gravity are taken by pouring parts of each of the samples into a hydrometer-jar and a reading taken. In heavy oils, some purchasers use one-third each of carbon-bisulphide, which 'cuts' the asphaltine oil and gasoline.
Shipping is usually done by a steam pump large enough to overcome the line-pressure ; electric pumps are also used for this purpose. Whenever possible, it is always desirable to have ship ping tanks at the lowest point of the property, in order to take advantage of a gravity flow, thus effecting a saving in pumping power. The use of concrete reservoirs for oil storage is not always satisfactory, as it is difficult to build a large reservoir through which the oil does not seep to some extent. It is often necessary to run water into concrete reservoirs to save the oil, the seepage sometimes amounting to hundreds of barrels per day. Oil should be shipped as soon as possible after being produced, as the evapora tion, especially in warm weather, is excessive. Oil standing in open earthen reservoirs has been known to shrink as much as 40% in the course of from 15 to 20 days. Oil, between 33 and 34 gravity, standing in tanks and exposed to the open air for 24 hours, has been known to lose 4% of its original volume by evaporation.
Gas Traps. The gas coming from the casing-head is usually caught and used under boilers or in gas engines, but the gas coming through the lead-line with the oil is often allowed to go to waste.
To prevent this, a gas trap as shown in Fig. 164 can be installed near the derrick. This trap consists of a sealed tank of about 25 barrel capacity. The oil enters the tank through a check-valve and is drawn off through a 3-in. outlet which has a float pressure valve to regulate the discharge. At the top, a relief-valve is placed to protect the tank from excess pressure, while the gas is drawn off below through a 2-in. line. This trap works satisfactorily on wells of moderate pressure working no sand.
The McLaughlin automatic gas trap (Fig. 165) is designed to recover the gas from a well under more difficult conditions, especially where there are quantities of sand and water present. The oil, sand and gas enter the device through the lead-line 'H' which leads directly from the well. The end of this lead-line is fitted with a tee into which is screwed a nipple '114' about 4 ft. long. On the upper end of this nipple is fitted a cast-iron valve 'A.' The faces of this valve are segments of a sphere. This valve engages a cast-iron valve 'B.' The valve seat is riveted to a movable tank `C.' The movable tank is suspended from a beam 'D' and is balanced by the weight box `E' filled with scrap iron. The beam 'D'
is supported by a frame 'F.' When in operation, the oil, sand and gas flow from the well through the lead-line 'H' into the trap at the point marked '4-in. oil inlet.' Before oil flows into the trap, the valve seat 13' is held firmly against the valve 'A' by the action of the counterweight 'E.' As soon as a sufficient amount of oil has entered the trap to over balance the counterweight, the tank 'C' carrying the valve seat 'B' moves downward and allows the excess of oil and sand to flow out between 'A' and 'B.' In the meanwhile all gas has been disengaged from the oil and flows out through the gas line connection 'G.' On a steadily flowing or pumping-well, the trap reaches an equilibrium so that the oil flows out continuously at the bottom and the gas at the top. On a head well the trap valve opens and closes rhythmically, maintaining at all times a perfect seal. The unbalanced upward pressure of the gas is sufficient to maintain, at all times, an oil seal of from 1 to 2 ft. in the bottom of the trap.
Other gas traps, similar in design, are made of three or four joints of casing, which is held in a nearly vertical position by guying to the derrick. The oil and gas enter the trap below, the gas rises to the top of the trap where it passes into a 2-in. line, while the oil is drawn off below. In some of the Russian fields, where production is obtained only by bailing, the use of the above-described gas trap is impossible, by reason of the casing being open at the surface. The gas is then caught by perforating the inside string 100 or 200 ft. below the surface and sealing the annular space between the two inside strings. A gas pump (Fig. 166) creates a suction, drawing the gas through this space and into the receiving line. The gas may also be obtained by tapping a hole through all the casing to the inside string 15 to 25 ft. below the surface and pump ing out with a gas pump.
As the bailer is being Constantly raised and lowered, more or less air is also caught, but considerable quantities of gas are saved. `Bleeders' or traps should be installed in the gas line to drain off any water or gasoline that accumulates, thus keeping the gas flow open. The amount of gas varies from a few feet per day in old pumping wells to several million feet in gas wells, and where several wells are connected, check-valves should always be placed in the line to prevent a high-pressure well from its gas into a low-pressure one. Gas lines and traps should be installed with as much care and foresight as the steam lines or water lines, for a great saving in fuel is effected by conservation of the gas, as far as is possible.