Establishment of Logging Evaluation Criteria for the Cementing Quality of Low-Density Cement Slurries

To provide a theoretical basis and criteria for the logging evaluation of the cementing quality of low-density cement slurries, the impacts of cement slurry density, cement sheath thickness, and cementing quality at the first interface on the conventional logging of cementing quality were analyzed according to the results of tests on acoustic characteristics at high temperatures and numerical simulation. The following understandings were obtained by the analysis: Affected by the outer diameter and thickness of casing, the difference in the relative amplitude of casing wave became increasingly obvious as the cement slurry density decreases. When there is a micro-annulus between the casing and the cement sheath, the amplitude increased monotonically with the the increase of cement sheath thickness and tended to be gentle when the cement sheath thickness was large. The micro-annulus significantly enhanced the amplitude of casing wave, especially for low-density cement slurry cementing. However, the effect of the cement slurry density weakened markedly after the thickness of the micro-annulus was increased to 5 mm. Depending on the analysis results, a log interpretation chart was established, and logging evaluation criteria were formulated for the cementing quality of low-density cement slurries. The evaluation criteria are expected to provide useful guidance for the logging evaluation of the cementing quality of low-density cement slurries in engineering practice.