Boulders at 450 ft

We recently drilled a borewell (Yelnanka, Bangalore). The total depth of the bore-hole is 1200 ft. we have major source is @ 1100 ft. The yield is ~2".

The borewell driller mentioned that there is some loose-soil @ 480 ft. To analyze this further, we checked with the camera and found that there are boulders b/w 450 ft. Installing a slotted-pipe casing will be a huge cost (~125/- per ft).

I've read in one of the blogs about the probability of having inner-casing only at the specific depth where boulders occur. Though there are a lot of technology advancements, I'm really not sure if this is possible. Can any of you suggest/provide-inputs if this is possible? If so, any contacts?

Appreciate your help in advance, mail