Preventing corrosion while drilling

Claim 1

A PROCESS FOR PREVENTING CORROSION IN THE DRILLING OF A WELL WITH FERROUS DRILLING APPARATUS WHEREIN THERE IS CIRCULATED THROUGH THE WELL A WATER-CONTAINING DRILLING FLUID, COMPRISING THE STEPS OF: (A) CIRCULATING THE DRILLING FLUID THROUGH THE WELL WHILE THE FERROUS DRILLING APPARATUS IS APPLIED TO DEEPEN THE WELL, (B) ADDING AN ALKALI METAL HYDROXIDE TO THE DRILLING FLUID CIRCULATED INTO THE WELL AT A TIME WHEN HYDROGEN SULFIDE FROM A SUBSURFACE SOURCE BEGINS TO INFUSE SUCH FLUID IN THE WELL AND IN AN AMOUNT SUFFICIENT TO PROVIDE A PH OF AT LEAST ABOUT 7 IN THE DRILLING FLUID CIRCULATED OUT OF THE WELL, (C) DISCONTINUING THE ADDITION INTO THE DRILLING FLUID OF SAID ALKALI METAL HYDROXIDE WHEN THE DRILLING FLUID CIRCULATED FROM THE WELL HAS A PH OF ABOUT 9, AND (D) DISTRIBUTING A WATER SOLUBLE ALKALI METAL SULFIDE INTO THE DRILLING FLUID IN THE WELL JUST PRIOR TO TERMINATION OF FLUID CIRCULATION THROUGH THE WELL WHILE HYDROGEN SULFIDE YET INFUSES THE DRILLING FLUID, SAID ALKALI METAL SULFIDE BEING INTRODUCED IN AN AMOUNT SUFFICIENT TO MAINTAIN THE PH OF THE DRILLING FLUID WITHIN THE WELL AT A VALUE GREATER THAN ABOUT 9 UNTIL FLUID CIRCULATION IS RE-ESTABLISHED AND THEN REPEATING THE FOREGOING STEPS.