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Abstract

A method is provided to estimate the pore volume of a formation occupied by hydrocarbon phase or phases, the method comprising the steps of: obtaining a first pulsed NMR log of the formation, the pulse sequence of the first NMR log comprising an initial 90.degree. radio frequency pulse, followed by a series of 180.degree. radio frequency pulses starting at a time period t.sub.cp1 after the initial 90.degree. pulse, and the series of pulses comprising magnetic pulses each separated by a time period 2t.sub.cp1 ; obtaining a second pulsed NMR log of the formation, the pulse sequence of the second NMR log comprising an initial 90.degree. radio frequency pulse, followed by a series of 180.degree. pulses starting at a time period t.sub.cp2 after the initial 90.degree. pulse, and the series of 180.degree. pulses comprising radio frequency pulses each separated by a time period 2t.sub.cp2 wherein the time t.sub.cp2 is a time that is different from t.sub.cp1 by an amount of time sufficient to separate resultant peaks of transverse relaxation times attributable to the hydrocarbon phase or phases within the formation; and determining, from the first and the second NMR logs, the pore volume of a formation occupied by hydrocarbon phase or phases within the formation. In a preferred embodiment, pore volume occupied by hydrocarbon gas is determined, and t.sub.cp2 is a time that is greater than that which results in the measured transverse relaxation time of the hydrocarbon gas being less than about 2.times.10.sup.-3 seconds and t.sub.cp1 is a time that is less than that which results in the measured transverse relaxation time of the hydrocarbon gas being greater than about 4.times.10.sup.-3 seconds.

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First Claim