Patent ID: 7511266

Claim:
A method for well logging for determining porosity (Î¦), sigma water apparent (Î£ WA ) and sigma log (Î£ LOG ), in oil and gas reservoirs, and simultaneously determining ash volume (V ASH ) and bulk density(Ï B ) in coal bed formations, comprising running a logging instrument through a wellbore traversing a plurality of earth formations, the logging instrument having a single source of neutrons for irradiating earth formations surrounding the wellbore and having two substantially identical Neutron-Neutron detectors being vertically spaced at differing distances from the single source of neutrons, said logging instrument having a Neutron-Gamma detector surrounded by a rare earth shield having a high capture cross-section and subsequent plurality emitting capture gamma radiation and a scintillation crystal acting in concert to moderate neutron activity in the wellbore and near-bore adjacent formations and detecting the intensity of a modified aggregate capture gamma radiation spectrum; detecting thermal neutrons by said Neutron-Neutron detectors; converting said detected thermal neutrons into electrical pulses; recording said electrical pulses as time events in counts/second for each of said Neutron-Neutron detectors; using a ratio of Neutron-Neutron detector count rates for pore volume determination; simultaneously detecting modified capture gamma radiation from the irradiated earth formation with said shielded Neutron-Gamma detector and converting the modified capture gamma radiation into equivalent electronic pulses; proportioning the electronic pulses into sequential low and sequential high energy ranges; recording the electronic pulses in a time event as counts/second; quantifying and comparing count rates of the sequential low and sequential high energy ranges to said pore volume of the irradiated earth formation to derive sigma water apparent (Î£ WA ), sigma log (Î£ LOG ), and earth formation matrix; and comparing said count rates of the sequential high energy range with that of the sequential low energy range in earth coal formation matrix to derive an ash volume (V ASH ) and bulk density (Ï B ) for any coal present in the formation matrix.