Ann: Daydream 2 Update, page-20

Leaving a slug of water in a well is standard practice,
you don’t leave wells “open”

you leave a hydrostatic head in the well ie; leaving a column of fluid heavier than any formation fluid or gases to effectively kill any unwanted activity in the well during periods of shut in

whats more interesting about this is the fact that the formation gases have high enough pressure to push our column of fluid enough to pressurise the hole… quite a lot of fluid for 4000m, you can imagine the weight of that column of water and what it would require to move it