17C-1 The Lease Pumper’s Handbook Chapter 17 Well Servicing and Workover Section C THE TUBING STRING C-1. Tubing and Casing Perforation. The relationship of casing perforations to tubing perforations is important to the performance of the well, whether it is a flowing well or produced by artificial lift. The lease operator must know if the tubing perforations are above or below the casing perforations or at the same level (Figure 1). This can be critical as to how much oil the well produces and the problems encountered. For wells that produce a lot of scale, production personnel operate under different philosophies. One school of thought is that the higher the tubing perforations can be raised above the casing perforations and still achieve a satisfactory daily production, the less the scale will break out of the water in the tubing and flow line. Some companies raise the tubing perforations a few feet above the casing perforations, while other companies move them much higher. Some operators maintain that if tubing perforations are placed even with or lower than the casing perforations, the reduction in reservoir pressure will increase daily production, resulting in increased income to solve the additional production problems. Other companies place the tubing perforations below the casing perforations even if it results in a tubing arrangement where the tubing has no mud anchor. A shop-made two-foot perforated joint is used. The joint is closed on bottom and has dozens of ½-inch holes drilled into it. A collar is used to screw it directly under the seating nipple. This reduces the length of the pump gas anchor to one foot or less. Companies favoring this method maintain that it gives the highest daily average production. The most typical tubing arrangement is to place the tubing perforations a few feet above the casing perforations. This maintains a small amount of liquid against the formation, instead of having a drained or dry matrix area at the bottom of the
