Systems and methods for processing acoustic cement evaluation data

One or more tangible, non-transitory computer-readable media storing instructions to:

• receive data points derived from a pulse-echo and a pitch-catch measurement, each data point comprising a first component based on measured flexural attenuation in a well having a casing, wherein the first component is the flexural attenuation or a flexural-attenuation-derived acoustic impedance, and a second component based on pulse-echo-derived acoustic impedance in the well having the casing;
• assign at least some data points having a second component value at or above an evanescence point to indicate that a material behind the casing is solid, wherein the evanescence point is a value of pulse-echo-derived acoustic impedance representing a transition from a medium that is able to maintain both a compressional and shear propagation to that of just shear propagation;
• and
• assign at least some data points having a second component value below the evanescence point to indicate that the material behind the casing is solid, liquid, or gas depending at least in part on a value of the first component, wherein the assigning includes using a first solid-liquid-gas model in which a gas threshold range comprising data points assigned to represent gas in the annulus is not directly adjacent to a liquid threshold range comprising data points assigned to represent liquid in the annulus, wherein the first solid-liquid-gas model comprises a range not providing a threshold indication of liquid, solid, or gas, the range being disposed between the gas threshold range and the liquid threshold range and corresponding to patchy dry debonding of cement behind the casing;
• determine based on the cement evaluation data points the nature of a material behind the casing, wherein the nature of the material includes one of the following:
• solid, liquid or gas.

A method comprising:

• measuring in a well having a casing an acoustic impedance via a pulse echo measurement and a flexural attenuation via a pitch-catch measurement
• receiving acoustic cement evaluation data points deriving from the pulse echo and pitch catch measurements, wherein the acoustic cement evaluation data points each comprise a first component representative of a flexural attenuation, wherein the first component is the flexural attenuation or a flexural-attenuation-derived acoustic impedance, and a second component representative of a pulse-echo-derived acoustic impedance;
• processing the acoustic cement evaluation data points using one or more initial solid-liquid-gas models to indicate when a solid, liquid, or gas is likely behind the casing, wherein the solid, liquid or gas thresholds of the one or more initial solid-liquid-gas models are defined based as a function of the first and second components;
• performing a posteriori refinement of the one or more initial solid-liquid-gas models to determine a refined solid-liquid-gas model that is more precise or more accurate, or more precise and more accurate, than the one or more initial solid-liquid-gas models;
• wherein refining the one or more initial solid-liquid-gas models includes refining one or more of solid, liquid or gas ranges, wherein the refined solid-liquid-gas model includes a first solid-liquid-gas model in which a gas threshold range comprising data points assigned to represent gas in the annulus is not directly adjacent to a liquid threshold range comprising data points assigned to represent liquid in the annulus, wherein the first solid-liquid-gas model comprises a range not providing a threshold indication of liquid, solid, or gas, the range being disposed between the gas threshold range and the liquid threshold range and corresponding to patchy dry debonding of cement behind the casing;
• and
• processing the acoustic cement evaluation data points using the refined solid-liquid-gas model,
• determining based on the processed cement evaluation data points the nature of a material behind the casing, wherein the nature of the material includes one of the following:
• solid, liquid or gas.