Recovery of oil from an underground formation

Claim 1

IN A PROCESS FOR WATER FLOODING AN OIL-BEARING FORMATION WHICH HAS BEEN DETERMINED TO BE PREFERENTIALLY OILWET WHEREIN FLOODING WATER IS INJECTED THROUGH AN INPUT WELL INTO SAID FORMATION OF OIL IS RECOVERED THROUGH A PRODUCING WELL, AND WHEREIN AN ADDITIVE IS USED IN SAID FLOODING WATER IN REVERSE THE WETTABILITY OF SAID FORMATION THE IMPROVEMENT COMPRISING OBTAINING AN AIR-FREE SAMPLE OF CRUDE OIL FROM SAID FORMATION, PLACING SAID CRUDE OIL IN CONTACT WITH A SMOOTH, SOLID SURFACE HAVIN A COMPOSITION SUBSTANTIALLY THE SAME AS THAT OF THE SURFACE EXPOSED TO THE OIL AND WATER WITHIN SAID FORMATION, PLACING WATER IN CONTACT WITH SAID SURFACE AND SAID OIL, DETERMING THE EQUILIBRIUM CONTACT ANGLE OF THE OIL-WATER INTERFACE WITH SAID SURFACE, REPEATING THE DETERMINATION OF THE CONTACT ANGLE USING WATER COMPOSITION IN WHICH AT LEAST ONE OF THE PH AND SALINITY IS CHANGED FROM PRECEDING WATER COMPOSITIONS UNTIL RANGES OF PH AND SALINITY OF WATER HAVE BEEN DETERMINED WHICH WILL MAKE SAID SURFACE PREFERENTIALLY WATER-WETTABLE IN THE PRESENCE OF SAID CRUDE OIL, AND ADDING TO SAID FLOODING WATER AT LEAST ONE MATERIAL SELECTIVE FROM THE GROUP CONSISTING OF ACIDS, BASES, AND SALTS TO ADJUST THE PH AND SALINITY OF SAID FLOODING WATER TO VALUES FALLING WITHIN THE RANGES WHICH WERE DETERMINED TO CAUSE SAID SURFACE TO BE PREFERENTIALLY WATER-WETTABLE.