Drilling fluids and method of using same

Claim 1

AN OIL BASE DRILLING FLUID COMPRISING AN OIL AT LEAST PART OF WHICH BOILS ABOVE 400*F. AND WHICH IS SELECTED FROM THE GROUP CONSISTING OF TOPPED CRUDE OIL, GAS OIL, KEROSENE, DIESEL FUEL, HEAVY ALKYLATE, FRACTIONS OF HEAVY ALKYLATE, AND MIXTURES THEREOF, AND AN AMOUNT OF A POLYMER OF 1-BUTENE SUFFICIENT TO REDUCE THE FLUID LOSS DUE TO FILRATION WITHOUT INCREASING THE VISCOSITY OF SAID DRILLING FLUID TO SUCH AN EXTENT THAT IT CANNOT BE CIRCULATED, SAID POLYMER HAVING BEEN PREPARED BY POLYMERIZING 1-BUTENE AT A POLYMERIZATION TEMPERATURE WITHIN THE RANGE OF ABOUT 100 TO ABOUT 500*F. AND A PRESSURE WITHIN THE RANGE OF ABOUT 100 TO ABOUT 700 P.S.I.G. IN THE PRESENCE OF A CATALYST ACTIVE FOR SUCH POLYMERIZATION AND COMPRISING, AS THE SOLE ESSENTIAL EFFECTIVE CATALYTIC INGREDIENTS THEREOF, CHROMIUM OXIDE AND AT LEAST ONE MATERIAL SELECTED FROM THE GROUP CONSISTING OF SILICA, ALUMINA, ZIRCONIA, AND THORIA, AT LEAST PART OF THE CHROMIUM BEING IN THE HEXAVALENT STATE AT THE INITIAL CONTACTING OF HYDROCARBON WITH SAID CATALYST.