Evaluation of cement density utilizing through-casing X-Ray logging method

Abstract

In the evaluation of cementing quality, quantitatively assessing cement density is crucial along with identifying the cementation degree at the interface using acoustic logging. While the ¹³⁷Cs-based formation density logging method is well-suited for density calculation, its reliance on open-hole environmental measurements poses challenges when inspecting cement density. This work focuses on the quantitative calculation of cement density while considering the radioactive hazards to the environment caused by ¹³⁷Cs source. The proposed approach utilizes a measurement system consisting of an X-Ray source and four gamma detectors. The gamma spectrum characteristics of each detector are analyzed, and the energy spectrum recorded by each detector is distinguished by different energy windows. A forward model is established to relate the gamma counts of each energy window to the formation and cement parameters. By employing a regularized Newton's method based on optimization technique, cement density can be calculated with a controllable error margin of within 0.015 g/cm³. Furthermore, even though X-Ray detection has lower sensitivity to formation parameters compared to ¹³⁷Cs, this method is capable of estimating formation density. Overall, the proposed approach enables the quantitative calculation of cement density and semi-quantitative calculation of formation density, therefore is of significance to the comprehensive evaluation of cementing quality.