METHOD FOR DETERMINING RESIDUAL HYDROCARBONS PRESENT IN A SUBTERRANEAN EARTH FORMATION

摘要

A method for determining residual hydrocarbons present in a subterranean earth formation by quantitatively determining the amplitude of the proton free-precession signal that is due to the protons contained in the residual hydrocarbons that are present in an interval of the subterranean hydrocarbon-bearing earth formation. The mud cake is removed or made permeable along a section of a well borehole adjacent the interval to be tested. An aqueous solution is injected down the well borehole and into the interval to be tested until the injected fluid occupies substantially all of the space within the well borehole and the interval to be tested that was previously occupied by other aqueous liquids in a zone extending into the interval to be tested at least substantially as deeply as a nuclear magnetism measuring device is to be responsive to proton free-precession signals. The solution which is injected contains sufficient dissolved paramagnetic material to provide a water phase nuclear magnetism thermal relaxation time that is too short to be responded to by the nuclear magnetism measuring device. A nuclear magnetism measuring device is disposed within the well borehole adjacent the interval to be tested and measurements are made of the responses with time of the device to (a) noise in the absence of polarization and (b) proton free-precession signal plus noise. At least one function of the noise and at least one function of the signal plus noise are combined to determine the signal amplitude at the end of the polarization.