Logging system and method for evaluation of downhole installation

A method of evaluation of a downhole installation, wherein the downhole installation comprises:

• a first pipe layer, a second pipe layer about the first pipe layer, an annulus between the first pipe layer and the second pipe layer, and a geological formation outside of the second pipe layer, the method comprising:
• exciting a flexural wave in the first pipe layer using an angled acoustic transmitter;
• receiving third interface echo data using angled acoustic receivers at different locations along the longitudinal extent of the pipes, the acoustic receivers including at least two receivers spaced apart from the transmitter so as to be located beyond the location where a peak in third interface echo amplitude is expected;
• processing the received acoustic data in order to:
• identify trends in the amplitude of the third interface echo as it propagates along the length of the pipe layers, calculate an estimated exponential decay for the third interface echo when reinforcement from other acoustic energy is disregarded, use this estimation to predict if the material behind the second pipe layer is fluid or solid, and analyse the third interface echo data in light of the determined material state in order to thereby evaluate material conditions in the annulus outside the second pipe layer.

A computer programme product comprising instructions that, when executed, will configure a computer apparatus to implement a method comprising:

• receiving acoustic data for a downhole installation that comprises:
• a first pipe layer, a second pipe layer about the first pipe layer, an annulus between the first pipe layer and the second pipe layer, and a geological formation outside of the second pipe layer;
• wherein the acoustic data comprises third interface echo data received by angled acoustic receivers at different locations along the longitudinal extent of the pipe layers, the acoustic receivers including at least two receivers spaced apart from the transmitter so as to be located beyond the location where a peak in third interface echo amplitude is expected;
• and
• processing the received acoustic data in order to:
• identify trends in the amplitude of the third interface echo as it propagates along the length of the pipe layers, calculate an estimated exponential decay for the third interface echo when reinforcement from other acoustic energy is disregarded, use this estimation to predict if the material behind the second pipe layer is fluid or solid, and analyse the third interface echo data in light of the determined material state in order to thereby evaluate material conditions in the annulus outside the second pipe layer.

A logging system for evaluation of a downhole installation, wherein the downhole installation comprises:

• a first pipe layer, a second pipe layer about the first pipe layer, an annulus between the first pipe layer and the second pipe layer, and a geological formation outside of the second pipe layer, the system comprising:
• a logging tool including an angled acoustic transmitter for exciting a flexural wave in the first pipe layer, and angled acoustic receivers spaced apart along the tool such that, in use, the receivers are at different locations along the length of the pipe layers, the acoustic receivers including at least two receivers spaced apart from the transmitter so as to be located beyond the location where a peak in third interface echo amplitude is expected, the receivers each being for obtaining third interface echo data from the second pipe layer;
• and
• a processor arranged to process acoustic data from the receivers in order to:
• identify trends in the amplitude of the third interface echo as it propagates along the length of the pipes, calculate an estimated exponential decay for the third interface echo when reinforcement from other acoustic energy is disregarded, use this estimation to predict if the material behind the second pipe layer is fluid or solid, and analyse the third interface echo data in light of the determined material state in order to thereby evaluate material conditions in the annulus outside the second pipe layer.