FINISHING OIL WELLS (CALIFORNIA PRACTICE) When the drillers have carried the hole into the oil sand their main work is done. The hole is now in the hands of the produc tion men, who are experts at handling wells.
In California two practices are com mon. The driller in one case sets the casing through the sand a few feet, and then drives a heavy wooden plug in the bottom of the casing. This latter is called a heaving plug and keeps the underlying soft beds of sand or shale from entering and clogging the casing. The oil sand is completely cased off by the oil string. To obtain the oil it is necessary to perforate this string at the points where the oil sand is reported. This is done in the hole.
Perforating Casing.—It is accom plished by lowering a cutting tool called a perforator in the hole. There are several types of perforators but the best type consists of a rolling knife which is a star-shaped, toothed wheel with five cutting points (see Fig. 43, page 109).
After the casing is perforated the well is bailed to remove the sand, sludge, and the drilling water. Such bailing may require several hours or several days. If the well flows, the control casing head regulates the flow, but if no flowing follows, bailing and pumping is necessary. Then a pump is placed in the well: One grave danger of casing perfo rated in the hole is the poor results often obtained. Clean-cut perfora tions are not the rule. Figure 44 shows a photograph of some casing perforated in the hole.
In the other cases where a rotary or circulator is used the string of casing is pulled and shop-perforated casing (see Fig. 45, page 111) is used at those points indicated by the well record as carrying oil sand. The perforated casing is inserted and the well is left full of mud fluid to keep back any oil. Oil-well screen may be inserted instead of perforated pipe.
Perforations vary greatly in size. They may have diameters of to Yi in. or lengths of 2 to 3 in. and iz in. wide. The holes may be spaced with centers 4 to 6 in. apart and the rows regular or they may be staggered. Each operator has a different idea
of the perforations necessary. No rule can be given. Practice in any field should be based on the best results in that field. The well is now ready for the pump.
Putting Well on the well gang starts work at the well by first setting on a casing head (see Fig. 46, page 112).
The drillers leave the casing a foot or two below the level of the floor. If the casing is 8% in. in size a bell nipple 8% in. in diameter at one end arid 6% in. in diameter at the other is screwed into the 8% in. and a Tee or a 4-way casing head screwed to that.
The 4-way head is useful where a heavy flow of oil is expected. However, for most wells a Tee head is sufficient. This head furnishes a means of controlling the oil. Lead lines to carry off the oil are screwed into one of the bushed openings of the 4-way head or the Tee and the well is ready for installing the pump.
Tubing with a working barrel for the pump at the bottom is next put in. This operation is much the same as was used with casing, only tubing is lighter and more readily handled. The well-crew in this case uses a light 4-line block for wells 3000 ft. deep and pulls from the calf wheel. A 2-line block may be sufficient for wells up to 1000 ft. in depth.
Heavy 3 in. tubing weighs 9 lb. per foot, or 180 lb. per joint of 20-ft. length. Two thousand feet would weigh 18,000 lb. or 9 tons.
Just before the last joint of casing is inserted a cast-iron tubing ring is placed under the top joint. The top collar of the tubing rests on this. Packing is placed between the tubing ring and its seat in the casing head. A gunny sack is sometimes used for packing and is wrapped under the collar of the tubing.
A nipple is next screwed into the top of the tubing and upon this nipple is a 3-way Tee (see Fig. 46). The side opening of the Tee is for the lead line which allows the fluid to flow off as it is pumped to the top. The upper opening is for the stuffing box which packs off the oil, and through which the polished rod works.