WIRELINE CONVEYED PERFORATING

There are two alternatives to be considered when perforating using wireline conveyed guns: casing guns and through-tubing guns. In both cases depth control is provided by running a Gamma Ray/CCL above the gun, and the guns are fired by electrical signal.

Casing Guns

Casing guns are large diameter perforators which cannot be run through normal tubing sizes. Therefore they must be used prior to running the test string and usually in overbalance conditions (completion brine or drilling mud). A shooting nipple should be used when using this method.

Through-Tubing Guns

Through-tubing guns are small diameter guns run through the test string. They can be used to perforate underbalanced, and hence eliminate the risk of damaging the formation with wellbore fluids immediately after perforating. Also, and especially in production situations, they can be run and fired with the well ‘nippled up’ and intrinsically safe. The gun size which can be run is limited by the tubing size.

5.4.1. Casing Guns Run In Overbalance

1) A safety meeting should be held before perforating. The safety aspects of perforating with casing guns are:

• The well must be stable with an overbalance mud

• There must be an adequate surface supply of kill fluid

• The BOPs should have been recently tested

• Radio silence must be in force before connecting the cable head until the guns are 100 metres below the sea bed.

On recovery of the guns, regardless of any indications that the guns have fired, radio silence must be in force before the guns are pulled back past 100 metres below ground level and until the cable head is removed.

2) The logging engineer should be given a diagram of the well showing the depths of all restrictions or changes in diameter.

3) Wireline should be rigged up as per the procedure in the Wireline Procedures Manual. 4) If perforating inside casing ensure the length of the gun assembly is less than the

distance between the blind rams and the grease head.

5) The distance between the top shot and the GR/CCL should be measured. It may sometime no be necessary to run a record the depth by GR or CCL if depth can be correlated to a sump packer or bridge plug.

6) The logging engineer must not connect the cable head until the Well Operations Supervisor, or his designated representative, has confirmed that radio silence is instated.

7) There is no restriction on running speed but care must be taken at any restrictions and when applying the brake.

1) The Logging Engineer must inform the Completion Supervisor, or his designated representative, when the guns are deeper than 100 metres below ground level.

2) Tie on depth to the CBL/VDL/GR/CCL log. Record a short section of film across the interval to be perforated showing at least five casing collars and the pup joint at the top of the reservoir section. The well should be perforated from the bottom upwards. 3) When the gun is on depth and ready to be fired, the logging engineer must inform the

Well Operations Supervisor, or his designated representative, and the driller, who should observe the well for losses or gains when the gun is fired.

4) Pull out at less than 5,000 ft/hour to avoid swabbing. 5.4.2. Perforating Procedures For Through Tubing Conveyed Guns

This operation will only be done once the cushion has been circulated into place.

Since only the first run can be perforated underbalance, it is common practice to perforate the best (highest permeability) zone first, otherwise the well should be perforated from the bottom upwards to minimise the chance of picking up debris on the cable.

1) A safety meeting will be held to review procedures and safety, specifically:

• The well is in underbalance and will be live after the first run

• The wireline BOPs should have been pressure tested

• The surface rig up must be pressure tested before each run

• Ensure the GR/CCL log across zone of interest is available.

2) The logging engineer should be given a diagram of the well and test string showing the depths of all restrictions or changes in diameter and he should check that he has sufficient weights for the maximum anticipated wellhead pressure.

3) Rig up wireline for a full bore drift run. Run in the hole and drift the tubing.

Note: Prior to arming the guns, the Offshore Installation Manager will ensure that conditions for safe operations exist. He should then inform base, standby vessels, supply boats and any relevant persons that the rig is passing into radio silence.

4) The wireline should be rigged up with the lubricator system, grease flow tubes, hydraulic stuffing box, tool trap, ball check valve and line wiper. Once radio silence has been obtained, rig up the perforating guns into the lubricator and pressure test. 5) Monitor the pressure in the ‘A’ annulus.

6) Ensure the surface tree master and swab valves are open and run in the hole with the perforating gun tool string.

7) Correlate the GR/CCL to the original GR log. Record a short section of film across the interval to be perforated showing at least five casing collars and the pup joint at the top of the reservoir zone. Do not run down into the perforations on subsequent runs. 8) Position the string at the desired perforating interval and fire the guns.

1) Pull out of the hole with the perforating string, taking care when passing through restrictions.

2) Repeat steps until the total required interval has been perforated. Do not flow the well while pulling the guns back through the tubing to surface.

2. Stop when the guns are at 100 metres below ground level until the Completions Supervisor, or his designated representative, confirms that there is radio silence.

1) The gun should be inspected at surface to check that all charges have detonated. Care should be taken as pressure can be trapped by debris behind the gun ports. A film record should be made of the job and the explosion register should be updated. 2) Open the well to flow and continue as per the Completion Programme.