Patent ID: 8471197

Claim:
A method for estimating a concentration of carbon dioxide (CO 2 ) in a formation penetrated by a borehole, the method comprising: conveying a carrier through the borehole; irradiating the formation with fast neutrons from a neutron source disposed at the carrier; detecting photons from the formation resulting from the irradiating using a first detector spaced a first distance from the neutron source and a second detector spaced a second distance from the neutron source that is greater than the first distance; and estimating the concentration of CO 2 from data acquired from the detecting; wherein the estimating comprises using (a) a first ratio of photons from thermal neutron capture interactions detected by the first detector to photons from thermal neutron capture interactions detected by the second detector or (b) a second ratio of photons from fast neutron inelastic scattering interactions detected by the first detector to photons from fast neutron inelastic scattering interactions detected by the second detector.