Fill sub

{
  "id": "MLC-T-OAG-001395",
  "term": "Fill sub",
  "field": "Oil and gas",
  "definition": "A short housing placed above the firing head of a tubing-conveyed perforating assembly to keep debris falling down the tubing or wellbore from reaching the head while the string is run in and held on depth before shooting. It holds or deflects the falling material away from the firing mechanism, so fouling does not stop the head from working. The sub sits in the string directly above the firing head, where falling debris would otherwise land.",
  "subject": "Perforating",
  "url": "https://mlchart.com/terminology/oil-and-gas/fill-sub/"
}