System for incorporating additives in drilling fluids

Claim 1

IN A DRILLING OPERATION WHEREIN AN AQUEOUS DRILLING FLUID IS PASSED DOWNWARDLY THROUGH A HOLLOW DRILL STRING WITHIN A BOREHOLE IN THE EARTH, DISCHARGED BENEATH A DRILL BIT AT THE LOWER END OF SAID DRILL STRING, AND PASSED UPWARDLY THROUGH THE ANNULUS BETWEEN SAID DRILL STRING AND THE BOREHOLE WALL. THE IMPROVEMENT WHICH COMPRISES PROVIDING A RESERVOIR OF DRILLING FLUID ADDITIVE WITHIN SAID DRILL STRING NEAR THE LOWER END THEREOF, SAID RESERVOIR BEING ISOLATED FROM SAID DRILLING FLUID PASSING DOWNWARDLY THROUGH SAID STRING, AND DISCHARGING SAID ADDITIVE FROM SAID RESERVOIR INTO THE BOREHOLE ANNULUS AT A POINT ABOVE SAID BIT IN RESPONSE TO FLUID PRESSURE WITHIN SAID DRILL SREING AS SAID DRILLING OPERATION PROGRESSES, SAID ADDITIVE BEING DISCHARGED IN QUANTITIES SUFFICIENT TO IMPROVE THE PERFORMANCE OF SAID AQUEOUS DRILLING FLUID AFTER SAID FLUID EMERGES BENEATH SAID BIT.