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How to Test Centralizer Starting Force and Running Force?

Bow spring centralizer is designed for primary cementing and applied in vertical, deviated and horizontal wells where low starting force and high restoring force are required.

Starting force and running force are key parameters that measure the quality of bow spring centralizers. Here, we'd like to briefly introduce what the starting force is, what the running force is, devices and samples required for starting force testing and running force testing, test procedures and results.

Starting force refers to the maximum force required to insert a centralizer into a specified wellbore diameter. Starting force values can vary depending on the installation methods. Running force refers to the maximum force required to move a centralizer through a specified wellbore diameter.

The maximum starting force shall be less than the weight of 12.19 m (40 ft) of medium linear mass as defined in Table 1. The maximum starting force shall be determined for a centralizer in new, fully assembled condition.

Table 1 Casing Centralizer Specification – Starting Force
Casing Diameter Medium Linear Mass Casing Maximum Starting Force
mm inch kg/m lb/ft N lbf
89 3-1/2" 14.7 9.91 1761 396
102 4" 16.9 11.34 2019 454
114 4-1/2" 17.3 11.6 2064 464
127 5" 19.3 13.0 2313 520
140 5-1/2" 23.1 15.5 2758 620
168 6-5/8" 35.7 24.0 4270 960
178 7" 38.7 26.0 4626 1040
194 7-5/8" 39.3 26.4 4697 1056
219 8-5/8" 53.6 36.0 6405 1440
244 9-5/8" 59.5 40.0 7117 1600
273 10-3/4" 75.9 51.0 9074 2040
298 11-3/4" 80.4 54.0 9608 2160
340 1-3/8" 90.8 61.0 10854 2440
406 16" 96.7 65.0 11565 2600
473 18-5/8" 130.2 87.5 15569 3500
508 20" 139.9 94.0 16725 3760
NOTE:
  • The specifications for restoring force for bow spring centralizers are based on the centralizer being installed as per manufacturer recommendations and tested with lugs on the casing. If the centralizer is tested over a casing collar, stop collar, or with an integral stop collar, the actual results obtained from that test can vary from the specifications. It should be noted on the test report how the centralizer was installed and the type of holding device used during the test. If a centralizer is tested in this manner, the test can no longer be considered a specification test and the results may or may not meet the specifications set forth in Table 1
  • Casing diameter refers to the liner sizes.
  • Medium linear mass casing refers to the plain-end weight.

Samples & Test Stand Preparation

Starting Force Test Procedures

  1. The starting force represents the maximum force required to insert the inner pipe into the outer pipe (after compensating for the weight of the inner pipe and attachments.) It is determined as described in starting force test procedure 2 to 6.
  2. Install a centralizer in new, fully assembled condition as shown in Figure 1 on the inner pipe over four equally spaced lugs, with each lug protruding not more than 6.4 mm (1/4") beyond the outer surface of the inner pipe.
    Note: Under field conditions, there are many different methods of attaching a centralizer to the casing. The starting and restoring forces for all types of holding devices may not be the same as the test results obtained using this procedure.
  3. The test assembly shall be within 5° of vertical.
  4. Lubricate the contacting surfaces with a petroleum-base grease before running the test.
  5. With the centralizer testing on the edge of the outer pipe, apply a load to the inner pipe to pull the centralizer into the outer pipe.
  6. Take readings of force used, from the time the load is first applied until the centralizer is completely inside the outer pipe. Report the maximum force as the starting force after compensation as in starting force test procedure 1.

Running Force Test Procedures

  1. The running force represents the maximum force required to slide the inner pipe inside the outer pipe once the force reading has become steady (after compensating for the weight of the inner pipe and attachments).
  2. The result of this test is not required to conform to a maximum value. However, the test shall be performed and the results recorded.
  3. The running force test may be performed with the starting force test, or carried out separately.
  4. Taking readings of force used from the time the centralizer is inside the outer pipe until the inner pipe is completely in place. Report the maximum force as the running force after compensation as in running force test procedure 1.
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