A number of unplanned scenerarios are possible, when carrying out a sand consolidation job. Below are a list of the most likely ones, and the corresponding contingencies procedure associated with them.
During the pre-job meeting, these contingencies should be discussed and where necessary additonal options included. Although this appendix applies to all epoxy based systems.
1 Problems setting the packer
If the packer cannot be set properly or it does not appear to be sealing, then unset the packer and try to reset. If there is any doubt about the integrity of the packer it should be pulled out of the hole and checked/replaced.
2 Pumping problems
- If pump fails and can not be repaired, use back-up pump.
- If a leak occurs in the surface lines, stop pumping and repair leak, where possible.
- If pumping pressure reaches the maximum allowable pressure with minimum flow rate, and the epoxy system has not yet reached the injection packer, then stop pumping and hold pressure at maximum allowable. The viscosity of the chemicals will reduce as the temperature increases, if the reaction is still in its initial phase. Pumping may then be possible again. If not, try the following option.
- If the epoxy system has entered the injection packer, and the pumping pressure reaches the maximum allowable pressure, then continue pumping, while checking the rate and pressure. Determine whether there will be enough time to pump and displace all the epoxy system into the formation. If it appears that this will not be possible, then:
- If sufficient rathole is available, unset the packer and run down to the bottom of the well. Then, while pulling out of hole, displace the epoxy system out of the tubing into the rathole.
- Alternatively, assuming coiled tubing is used, unset the packer and pull out of the hole without pumping. This will keep the epoxy system in the coiled tubing and away from downhole accessories (eg sub-surface safety valve nipple, sliding side-doors, side pocket mandrels, etc) and from the Xmas tree, BOP's, etc. In the lubricator or the mousehole circulate out the epoxy system with the displacement fluid, ensuring that returns are directed to the waste tank.
If a snubbing unit is used, then the safest solution is to immediately circulate out the epoxy system back to surface and into the waste tank, with displacement fluid, followed by brine. Unfortunately, this will mean that the completion tubing, downhole accessories and the Xmas tree will all come into contact with the epoxy system. There is no guarantee that the displacement fluid will completely clean all the contaminated surfaces.
3 Problems with the shear plugs
If there is no indication of a shear plug bumping, only pump an extra 40 litres.
Then, stop pumping. Overdisplacing of the epoxy system may lead to the near wellbore region having lower strength and lower return permeability, because of the displacment fluid contaminating this region. Volumes in the tanks should be continuously monitored. The flowmeter readings should not be relied on solely for rates and volumes pumped.
4 Problems when unsetting the packer
If the packer cannot be unset, then apply maximum overpull. If this fails, displace 150 litres displacement fluid out of the tool and try to unset again. If the packer is still set, then displace a second 150 litres displacement fluid out of the tool and try to unset again. If that fails, allow the the epoxy system to cure (check viscosity build up of sample) and then spot displacement fluid around the packer. Apply maximum pull to shear the weak point. Circulate displacement fluid out of the tubing and pull out of hole.