Determination of contamination of underground formation samples by drilling fluid using radiation absorption analysis methods

Claim 1

IN THE PROCESS OF ANALYZING A SAMPLE FROM AN EARTH FORMATION FOR INDIGENOUS OIL, WHEREIN A DRILLING FLUID CONTAINING OIL IS PRESENT AT SAID EARTH FORMATION AT THE TIME MECHANICAL PENETRATION OF SAID EARTH FORMATION TO OBTAIN SAID SAMPLE IS CARRIED OUT AND CONTAMINATION OF SAID SAMPLE WITH SAID OIL CONTAINED IN SAID DRILLING FLUID CAN OCCUR, THE STEPS COMPRISING: (A) DISSOLVING A COMPOUND SELECTED FROM THE GROUP CONSISTING OF ANTHRACENE, ALKYL SUBSTITUTED ANTHRACENES, AND CHLORINATED HEAVY HYDROCARBONS IN SAID OIL CONTAINED IN SAID DRILLING FLUID, (B) PASSING SAID DRILLING FLUID TO SAID EARTH FORMATION, (C) MECHANICALLLY PENETRATING SAID EARTH FORMATION AND OBTAINING A SAMPLE THEREFROM, (D) RECOVERIG SAID SAMPLE FROM SAID EARTH FORMATION, (E) WASHING DRILLING FLUID FROM THE SURFACE OF SAID SAMPLE, (F) EXTRACTING SAID SAMPLE WITH A SOLVENT FOR OIL TO OBTAIN A SOLUTION OF EXTRACT, AND (G) THEREAFTER ANALYZING SAID SOLUTION OF EXTRACT FOR OIL CONTAINED THEREIN BY PASSING THROUGH SAID SOLUTION PENETRATIVE RADIATION AT WAVELENGTHS INCLUDING THOSE WHICH ARE ABSORBED BY SAID COMPOUND SELECTED FROM THE GROUP CONSISTING OF ANTHRACENE, ALKYL SUBSTITUTED ANTHRACENES, AND CHLORINATED HEAVY HYDROCARBONS AND MEASURING THE INTENSITY OF THE TRANSMITTED PENETRATIVE RADIATION TO DETERMINE ABSORPTION THEREOF WHEREBY ABSORPTION OF SAID PENETRATIVE RADIATION BY SAID COMPOUND SELECTED FROM THE GROUP CONSISTING OF ANTHRACENE ALKYL SUBSTITUTED ANTHRACENES, AND CHLORINATED HEAVY HYDROCARBONS INDICATES CONTAMINATION OF SAID SAMPLE BY SAID OIL CONTAINED IN SAID DRILLING FLUID.