Nitrogen cushion

{
  "id": "MLC-T-OAG-002541",
  "term": "Nitrogen cushion",
  "field": "Oil and gas",
  "definition": "A column of compressed nitrogen placed in the tubing or drill string above the liquid, used in drillstem testing and tubing-conveyed perforating to lower the hydrostatic pressure acting on the formation and set the underbalance when the tester valve opens or the guns fire. Because gas is compressible, the column also softens the first surge of fluid entering the string. Nitrogen is chosen because it is inert and much lighter than any liquid.",
  "subject": "Perforating",
  "url": "https://mlchart.com/terminology/oil-and-gas/nitrogen-cushion/"
}