Monte-Carlo N-Particle (MCNP) simulations and laboratory prototype testing suggest detection capabilities with high energy x-rays of air voids and water defects well past the first well casing. Simulation results show detectability of air voids with diameters less than Ø 0.15" several inches into the concrete structure past the first casing. Laboratory experiments with realistic phantoms using high-energy x(γ)-rays show good discrimination between air voids, water defects, and no defects (cement only). This novel imaging technique is complementary to more conventional inspection modalities such as acoustic or electromagnetic imaging. State-of-the-art acoustic imaging techniques usually investigate the bond between first casing and surrounding cement structure. Current electromagnetic imaging tools typically target detection of material loss in the innermost metal casing but cannot detect defects in the surrounding concrete structure. A high resolution x(γ)-ray imaging modality that can image metal and concrete defects well past the first casing should be greatly beneficial for well integrity inspection of multi-casing wells at intermediate-to-surface depths along major ground water zones. An extensive tradeoff analysis of performance parameters such as minimum defect size, sector angle resolution, depth resolution, penetration depths, and logging speed will be presented and benefits and drawbacks of the proposed technology will be discussed.

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