Bonding to casing material characterization is a topic of interest in the context of well barrier evaluation. There is a consolidated need directed to log data interpreters to answer questions related to the type of material present in the casing annuli of a given well. The objective of this work is to explore the possibility to provide a complementary answer to current general acoustic impedance and attenuation practice.
We reiterate that knowledge about the density of the annuli material can reduce the well barrier evaluation uncertainty. We are describing and exemplifying a rapid method to estimate the "pseudo – density" of the material in the annuli at the time of data acquisition. We define "pseudo-density" as the ratio between estimated impedance (from ultrasonic pulse-echo) and annuli apparent velocities (from ultrasonic oblique incidence techniques). Resulting "pseudo-density" maps are constrained with prior information from geology, logging, and drilling data. This allows the interpreter to judge the uncertainty in the current interpretation practice and contextualization of the annuli material into the borehole reality.
The examples provided show that when the underlying physics principles are met, the results are clear and a robust interpretation at scale along the entire logged path is possible. The estimated complementary results are affected by inherent errors and uncertainty associated with acoustic impedance and velocity estimation. However, using prior knowledge information, intervals with high uncertainty (such as unusually high impedances or large errors in the velocity estimation) are flagged providing the interpreter with information background easy to be used for final delivery.
Along with standard applications, the proposed method includes the basic mandatory tool for evaluating, validating, and incorporating the forecasted growth based on nuclear integrity logging behind the casing evaluation techniques.