Casing inspection using pulsed neutron measurements

摘要

A method for evaluating wellbore conduit condition includes using measurements of at least one of (i) inelastic gamma rays made during emission a burst of neutrons into the conduit from within the conduit at at least one spaced apart location from a position of the emission and (ii) epithermal neutrons or capture gamma rays therefrom detected at at least two spaced apart locations from the position of the emission within a selected time after the emission. The at least one of the measurements of inelastic gamma rays and epithermal neutron or capture gamma ray counts are characterized to estimate an amount of loss of iron in the conduit.

主权项

1. A method for evaluating wellbore conduit condition, comprising:
accepting as input to a computer measurements of at least one of (i) inelastic gamma rays made during emission a burst of neutrons into the conduit from within the conduit at at least one spaced apart location from a position of the emission and (ii) epithermal neutrons or capture gamma rays therefrom detected at at least two spaced apart locations from the position of the emission within a selected time after the emission; in a computer, characterizing the at least one of the measurements of inelastic gamma rays and epithermal neutron or capture gamma ray counts to estimate an amount of loss of iron in the conduit; and displaying a parameter related to the amount of iron loss, further comprising using measurements of inelastic gamma rays detected during the emission at at least a second location spaced apart from the at least one location and in the computer determining a ratio of inelastic gamma rays detected at the at least one location and the at least one additional location and using the ratio to estimate a condition of the conduit, wherein the estimating the condition from the ratio comprises measuring the ratio in a known undamaged section of the conduit and comparing to the ratio determined in the wellbore conduit, and further comprising using a ratio determined from measurements of inelastic gamma rays made proximate a wall of the conduit and a ratio determined from measurements of inelastic gamma rays made proximate a center of the conduit, and in the computer comparing the ratio from proximate the wall to the ratio proximate the center to identify portions of the conduit having iron loss.