GAUGING OIL AND GAS WELLS After the water and sediments have been drawn off, he inserts a rod graduated to quarter inches, by means of which the number of inches of oil in the tank is found. This information enables us to compute the number of barrels in a tank if its exact size is known. Tanks used for such purposes are measured or "strapped" by the purchaser's engineer, who determines the size and computes a table from which the number of barrels per inch can be calculated.
Wooden tanks built up of staves and held together by means of hoops when moved about and set up at various points will not be the same size at all times, and for this reason it is neces sary that all tanks used for gauging purposes should be strapped. When the measurements have been made the tank is numbered, and the position of the hoops are clearly marked by a white washed line so that if any of them are displaced they may be noticed. As wooden tanks arc smaller at the top than at the bottom, the amount of oil at a distance of one inch will vary and be more at the bottom than at the top. For instance, in a 250 barrel wooden tank, an inch of oil at the top will indicate about 21 barrels of oil; at the bottom about 24 barrels; for a rough estimate 21 barrels of oil per inch may be considered a good average. Iron and steel tanks being cylindrical the ratio of the number of barrels per inch will be the same at any point.
The gauger determines the temperature and the number of bar rels of oil in the tank and allows the oil to run into the line, in -which the oil is carried either by gravity or pumped to the storage tanks. It is advisable to run the oil at as frequent intervals as possible to prevent the evaporation of large amounts of oil. The producer is given a memorandum (Fig. 12o) and a similar one is retained by the gauger and turned in at head quarters. In the winter many oils become so heavy that it is necessary to "steam" them before they can be run.
The volume and efficiency of a gas well depends upon the static and dynamic pressures existing in a well. The dynamic pressure, which is the open flow volume is measured with a Pitot-tube, which is a U-tube, equipped with a scale of inches divided into tenths, the zero point being half-way along the tube and the graduations extending in both directions from it. The tube is filled with water or mercury so that the level of the liquid on each side of the scale will be at zero. (Fig. r2r.) By
means of proper adjustable fittings the gauge is held over the escaping gas from the well so that the pressure of the flowing gas may be indicated by the distance between the different levels of the liquid in the U-tube caused by such pressure. By referring to a table the size of the gas well's volume may be computed if the diameter of the opening of the well mouth is known.
The static pressure, which is the so-called closed or "rock pressure," may be determined when the well is properly fitted up so that an ordinary steam gauge (Fig. 122) may be so con nected that it will indicate the pressure of the well. The rock pressure of a well is the ultimate pressure that is recorded by such a steam or spring gauge.
The actual procedure in measuring the open flow volume of a well is as follows: allow the well to "blow off" to its natural pressure, hold the Pitot-tube or U-gauge on level with the top of the opening about one-third of the way in; note the number of inches between the levels of the liquid on each side of the tube, also determine the size of the opening. For instance, if the liquid which we are using in the tube is water, and is held over the flow of gas, we note that the liquid has been depressed five inches on one side and raised five inches on the other the total distance between levels will be ten inches, and the size of the casing through which the gas is escap ing is four inches in diameter, then referring to our table, under ten inches of water through a 4-inch opening we find the figure 1,904,64o, which will be the number of cubic feet of gas flowing out of the well in twenty four hours. If mercury instead of water is used, the same number of inches of mercury through a 4-inch opening will be seen to be 7,038,72o cubic feet per twenty-four hours. If the size of the well is too great, so that neither water nor mercury can be used, the steam gauge may be employed by holding it over the opening in the same manner as we hold the Pitot-tube; the volume of the well may be determined by noting the number of pounds indicated by the gauge, and the volume computed from the table similarly as with water and mercury. Thus if the gauge indicates 25 pounds through a 4-inch opening, the volume will be shown by the table to be 13,678,08o cubic feet of gas per twenty-four hours.