November 24, 2004
Following are guidelines for the use of coiled tubing (CT) during well plugging operations. These guidelines are applicable as field rules in the districts and are subject to change.
- All coiled tubing units shall be equipped with adequate weight and depth measuring equipment. Depth meters shall be calibrated every 90 days and should be installed as far away from the injection head as possible to avoid errors caused by vibration. A record showing the calibration date, calibration method (including length of pipe calibrated), and the name of the calibrator shall be maintained on the coiled tubing unit. A new calibration shall be required any time the coiled tubing or meter is replaced. All depth meters shall be clearly visible from ground level.
- No minimum tubing diameter requirement is necessary. For coiled-tubing cleanouts, however, the ratio for casing to tubing diameter (OD:OD or ID:ID) should not exceed 5:1 so that the fluid velocity in the casing is adequate to remove fill and not merely drill a hole through it.
- Cement plugs shall be placed with static coiled tubing until full circulation is established and 100 linear feet of cement (calculated) is placed above the tubing tail. Once both requirements are met, the tubing may be moved up the hole at a rate equal to the cement fill-up. Exceptions may be made when a danger exists of the tubing becoming stuck, such as in a small diameter casing or liner. In such a case, only the 100 linear feet requirement is necessary until the tubing tail is above the liner top, at which point the tubing must remain static until full circulation is established or the plug is in place. Squeeze cementing operations may be performed with coiled tubing. However, as in all bradenhead squeezes, casing integrity is necessary.
- Cement plugs should be tagged with the circulating pumps on if the initial tagging attempt with the pumps off results in an inconclusive, gradual weight loss. The minimum outside tubing diameter for tagging a plug shall be 1¼-inch, but exceptions can be made if severe restrictions in the wellbore require use of a smaller diameter.
