Can casing pipe insertion dislodge bore well blockage?

Question

First we had drilled to rock-bed at 170’,& inserted casing pipe.
Continued drilling & got water at 275’ but a low flow.
At 400’ met a good water strata.
Drilled to 600’ as insurance against water table level drop in poor rainfall years.
Withdrew drill. Inserted submersible pump. Found a
blockage at 275’, aborted the pump installation.
Referred matter to geologist. His opinion is that water strata at 275’ may be having loose boulders that move into bore and block it. Advised us flush the bore & insert MS casing to 300’ depth to :-
-prevent rocks from blocking the bore / falling into the bore
-protect the subm pump
-facilitate pump removal for maintenance.
Q: For flushing bore,removing drill & insert casing to 275’ time needed 8 hours. If within this time rocks move again into bore WILL PRESSURE OF MS CASING INSERTION BE SUFFICIENT TO DISLODGE ROCK BLOCK TO COMPLETE CASING INSERTION? OR CAN BLOCK PREVENT CASING INSERTION? IF THIS HAPPENS WHAT DO WE DO?

Answer 1

It is hard to say what will happen between the time you reopen the well bore and insert the casing. If you can't get the casing down without damaging it, you may have to ream the hole and try again.

If that doesn't work, try an old oil field trick. Set a brush plug below the loose formation (a small inverted pine tree pushed down the hole with a couple of empty cement or burlap bags on top of it) dump a five gallon bucket of pea gravel on top of that. Run the drill stem back in the hole and pump neat cement (6 gal of water per bag of portland cement, no sand no gravel, just cement) on top of the brush plug. The trick is getting enough cement to seal off the formation without collapsing the brush plug. If the driller has a packer or a bridge plug, that would be better, but a brush plug will work. Wait at least three days. By that time the cement should set up and cemented off the offending formation. Then drill through it.

It is worth a try.

Answer 2

My two brothers are the petroleum geologists...but...in answer to your question, obviously a clean bore is preferable. MS casing dislodging the block...depends on the projection into the bore hole, longitudinal length of the blockage, rock composition and downward force of the casing insertion.