Common Problems Affecting PDC, Natural and Thermally Stable Diamond Bit Performance

COMMON PROBLEM   PROBLEM CAUSE   PREFERRED ACTION
Difficulty going to bottom   -Previous bit under gauge.
-New bottom hole assembly.
-Collapsed casing.
-Out of drift.
-Bit oversized.
-Stabilizer oversized.		   -Ream with roller cone bit. When reaming to bottom, pick up and ream section again. If difficulty remains, check stabilizers. Roll casing with smaller bit. Use centre bit or reduce bit size. Gauge bit with API gauge; if not in tolerance, replace bit. Replace with correct size stabilizer.
Low pressure differential across nozzles or bit face   -Flow area too large.
-Flow area too low.
-Different drilling parameters than designed for.
-Washout in drill string.		   -Increase flow rate and correct on next bit. Increase flow rate/strokes. Change liners. Attempt to optimize, on next bit change flow area. Check bit pressure drop, drop soft line, trip to check pipe and collars.
High pressure differential across nozzles or bit face   -Flow area too small.
-Excessive flow rate.
-Diamond too small for formation.
-Bit partially plugged (formation impaction)
-Formation change.
-Ring out.
-Downhole motor stalled.		   -Reduce flow rate, on next bit change flow area. Reduce flow area. If ROP acceptable, change on next bit. If ROP unacceptable, pull bit and use bit with correct diamond size. Check off bottom standpipe pressure. Let bit drill off, circulate full volume for 10 minutes while rotating. Check off bottom pressure again. Pick up, circulate, resume drilling at higher RPM, reset, drill off test. On and off bottom pressure test, pull bit. Refer to manufacturer’s handbook.
Fluctuating
standpipe pressure		   -Drilling through fractured formation.
-Formation breaking up beneath bit.
-Stabilizers hanging up.
-Equipment failure.		   -If ROP acceptable, continue.
Check equipment.
Try combination of lighter weight and higher RPM. Check over pull. Check stabilizers on next trip. Repair equipment.
Bit won’t drill   -Bottom not reached.
-Stabilizers hanging up or too large.
-Formation too plastic.
-Establishing bottom hole pattern.
-Core stump left.
-Bit balled		   -Check tally. Check torque, over pull.
Check pressure increase flow rate, decrease/ increase bit weight, RPM. Can take up to an hour. Attempt to carefully drill ahead with low bit weight. Back off and increase flow rate, then slug with detergent or oil.
Slow RoP   -Not enough weight on bit; hydraulic lift.
-RPM too low/high -Plastic formation.
-Change in formation.
-Overbalanced.
-Diamonds flattened off.
-Cutters flattened
-Pressure drop too low.
-Wrong bit selection.		   -Increase weight on bit; -Increase/decrease rotary. Reset drill off. Reset weight. Reset drill off. Accept ROP. Pull bit. Compare beginning and present drops new bit may be required. Increase weight. Pull bit.
Increase flow rate new bit may be required.
Pull bit.
Excessive torque   -Excessive weight on bit.
-Slow RPM.
-Stabilizers too large.
-Collars packing off.
-Bit under gauge.		   -Reduce weight and RPM. Increase rotary. Decrease weight. Check bottom hole assembly; stabilizers should be 1/32” to 1/16” under hole size. Increase flow rate and work. Pull bit.
Bit Bouncing   -Slip-stick action.
-Broken formation.
-Pump off force.		   -Change rotary weight combination. Reduce rotary speed and weight. Increase weight. Decrease volume.