After a filter pack and bentonite seal have been placed, how far can a well screen section be moved vertically?

• A. The length of the filter pack above the screen
• B. Twice the filter pack length
• C. The length of the screen above the pack
• D. The bottom of the borehole

Answer: (A)

The key idea is that the screen must stay within the packed annulus that surrounds it. After you place the filter pack around the screen and add the bentonite seal above, the amount of packed material above the screen provides the limit for vertical movement. You can reposition the screen only by the distance equal to that length of filter pack above the screen; moving more would pull the screen out of the packed zone, breaking the seal and reducing the effectiveness of filtration around the screen. In short, the screen can be moved vertically only as far as the length of the filter pack that sits above it, to keep a continuous, properly packed annulus around the screen.