A gravel pack around a well screen serves as a sand-control barrier that protects the screen and the pumping system. By placing properly graded gravel in the annulus between the screen and the formation, formation sand and fines are filtered before they can enter the screen. This stabilization of the surrounding formation reduces the amount of sand and silt that would otherwise be produced with the water and helps prevent erosion around the screen. The result is a longer-lasting screen with fewer plugging and wear issues, since the gravel pack provides a permeable, protective filter bed that allows fluid to flow while keeping sand out. The other options misstate the function: sealing the top of the borehole or curing cement around it are cementing tasks, not gravel-pack purposes, and the gravel pack isn’t primarily there to filter water after pumping.