NMR logging of natural gas reservoirs

A method to estimate a formation pore volume occupied by hydrocarbon gas utilizing a NMR logging tool, the method comprising the steps of:

• obtaining a first pulsed NMR log of the formation, the first NMR log utilizing a pulse sequence 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 180.degree. pulses comprising radio frequency pulses each separated by a time 2t.sub.cp1 wherein the time t.sub.cp1 is a time which results in the measured transverse relaxation time of the hydrocarbon gas being within a range of measured transverse relaxation times that are detectable with the NMR logging tool utilized;
• obtaining a second pulsed NMR log of the formation, the second NMR log utilizing a pulse sequence 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.cp2 after the initial 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 hydrocarbon gas within the formation;
• and
• determining from the first and the second NMR logs the formation pore volume occupied by hydrocarbon gas.

A method to estimate a formation pore volume occupied by a hydrocarbon phase or phases utilizing a NMR logging tool, the method comprising the steps of:

• obtaining a first pulsed NMR log of the formation, the first NMR log utilizing a pulse sequence 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 180.degree. pulses comprising radio frequency pulses each separated by a time 2t.sub.cp1 wherein the time t.sub.cp1 is a time which results in the measured transverse relaxation time of the hydrocarbon phase or phases being within a range of measured transverse relaxation times that are detectable with the NMR logging tool utilized;
• obtaining a second pulsed NMR log of the formation, the second NMR log utilizing a pulse sequence 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.cp2 after the initial 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 formation pore volume occupied by the hydrocarbon phase or phases.