Water cushion

{
  "id": "MLC-T-OAG-004092",
  "term": "Water cushion",
  "field": "Oil and gas",
  "definition": "A column of water placed in the test string or tubing above a packer or perforating gun before a drill stem test or underbalanced perforating. Because water is lighter than drilling mud, the cushion sets a chosen pressure difference between formation and wellbore at the moment the tool opens, which governs the initial surge and drawdown, and it limits the differential pressure across the packer and tools. Its height is calculated from the expected formation pressure.",
  "subject": "Well Completions",
  "url": "https://mlchart.com/terminology/oil-and-gas/water-cushion/"
}