Perforating and pipe recovery operations performed with coiled tubing provide logistical and technical advantages in certain situations. Conventional tubing conveyed firing head adapters have been redesigned to be conveyed by this method which is activated by coiled tubing pressure. Summary results are presented from 26 different operations performed within Trinidad. Horizontal and highly deviated wells can benefit from this option when electric line methods may be limited due to hole angle or dog leg severity. Depth control is addressed by means of a correlation run or use of profile location mechanisms which can be incorporated in the perforating assembly. A review of pressure deployment systems is provided for thru-tubing underbalance perforating of long sections. This system has added value to the production operator by minimizing space constraints of offshore platforms and limiting additional equipment needed for remote locations.
A hydraulic style detonation mechanism is activated by the combination of applied coiled tubing pressure, and hydrostatic pressure (Fig. 1). As pressure in the coil increases to the shear stud value, a piston is driven into the initiator which detonates the charge. Depending on job conditions, the firing head can be equipped with a circulating port after detonation, or it can remain a closed system which prevents fluid loss to the wellbore and formation. For the closed system, a tubing pressure-activated hydraulic disconnect is used which operates on the differential pressure between the coiled tubing and production tubing. The calculation methods shown in the Appendix should be followed to verity that 20 percent or more shear value exists between the hydraulic firing head pressure and the disconnect pressure. This firing mechanism provides the ability to deploy hollow steel carrier perforating guns, strip charges or jet cutters.
Depth Control. Depth correlation is required for perforating and pipe recovery operations. Several methods are used which include a tubing profile locator that can be run in conjunction with the perforating assembly. Also a memory GR/CCL or drift nozzle can be run to locate a tubing profile at a known depth which requires an additional coiled tubing well entry before perforating. Typically, a stripe is painted on the coil when an additional trip is made and can be used to corroborate the depth. It should be noted that elongation of the coil can occur during successive trips that could be as much as 2 in. per 1000 ft. based on field results.
Wellbore Trajectory Problems.
Deviation. Field experience indicates that 70 degree hole angle is the upper limit for electric line conveyance of perforating guns in wells with a kick off point of 3000 ft. and a 9000 ft target zone. However, lower hole angles with higher departures may decrease the electric line access threshold to as low as 60 degrees due to frictional weight loss. Deviations above 70 degrees will require coiled tubing to reach the target depth for most situations.
Corkscrewed tubing or Wellbore Irregularities. Completion practices which result in corkscrewed tubing can also limit the ability of electric line from reaching the objective. Coiled tubing entry in this environment requires extreme caution to prevent becoming stuck due to friction between the coil and production tubing, which may not be apparent from wireline drift runs.