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CORE DRILLING

TROUBLE SHOOTING

Problem / DifficultyPossible ReasonSolutions / Actions

Low core recoveryfractured rocksoft, fragile rockloose, unconsolidated rock( call for help (specialist)*( use core catcher( use larger bit diameter( use double or triple core barrel( reduce mud pressure( increase / decrease weight on bit( increase / decrease RPM( use special mud additives like polymers, bentonite( use foam as a circulating agent

Slow progresshard formationinsufficient flushing at bitcaving in( use different bit (larger diamonds)( use different design for flushing( increase RPM( increase weight on bit( decrease drilling mud pressure

No returnsfractured formationpermeable sandkarst holes( drill without returns (with water)( reduce density of mud( use foam as flushing agent

Drill string stuckbad circulationcaving in of wallsnot a straight hole( use full pulling capacity( use full pumping capacity of mud( disconnect above blocked tubage( try to fish with special tools( abandon hole

Deviation of holehigh pressure on bitoblique angle of stratificationchange from hard to soft formation

( take measurements every 50 - 100 m( reduce weight on bit when crossing formation boundaries( use special deviation tools to bring hole back

Blow outyou have hit oil or gas( buy concession and get rich

* Drilling specialist: FORALITH AG, Gossau SG, Tel: 071 388 89 29, Mr. Pingel

Q:\SEKR\ZI\DIVERSE\trouble.doc