TECHNICAL INFORMATION

Downhole solids deposition

So the solids exist - how, when and where are they loosened and deposited?

Offshore the tubing is probably racked, numbered, measured, flushed and drifted. The threads will be checked and "doped" with suitable thread compound.

When the joints are lifted into the derrick, mechanical impact will loosen rust and millscale prior to stabbing into the box of the previous joint.

As the pipe is run, the external tubing surfaces will abrade against the casing and release corrosion and millscale debris into the annular space.

At depth, a sequence of pressure testing will commence. As the pressure is applied and bled-off, further scale will be released from the tubing wall by flexing of the material.

Passage of wireline tools in the tubing bore will abrade and release debris, especially in the more highly deviated wells.

Corrosive action will progressively lift the more tightly adhering scale.

The sum total of the above is various sizes of millscale and corrosion debris settling-out at different rates and stages-the smaller particle sizes staying in suspension longer The debris will accumulate at the bottom of the well, in the annulus on top of the packer and on any device installed in the well bore. When the well is brought on production or injection, further debris will be removed by the flow effect, adding to the accumulations.