Abstract
Abstract
In many cases, we observe that log responses from ultrasonic, flexural, and sonic logs do not meet the expectations of the executed cementing job without showing major issues. Also, often the logs do not even see the cement behind the casing. These scenarios are most often caused by either a wet microannulus or a dry microannulus. Often the effect of a microannulus is not recognized, and this may lead to the incorrect assessment of cement condition. If this issue is not resolved, it can lead to costly and unsuccessful attempts at intervention.
Successful detection of microannulus was done using the combination of flexural attenuation, ultrasonic pulse-echo technology, third interface echo (TIE) and cement bond log-variable density log (CBL-VDL) measurements. If a dry microannulus is present, ultrasonic acoustic impedance (AI) is more affected than the sonic log and responds earlier to the dry microannulus. If a wet microannulus is present, the sonic log is more affected than ultrasonic AI and responds earlier to a wet microannulus.
In this study, we encountered several wells with varying sizes of dry and wet microannulus. In some wells, a large size dry microannulus was observed and the affected ultrasonic data were mainly showing gas as if no cementing had been conducted. Some wells had a small dry microannulus and the affected ultrasonic measurements showed the annulus to be filled with liquid and cement. Apart from this we also observed several wells with varying sizes of wet microannulus affecting the ultrasonic and sonic measurements by varying degrees and ultimately affecting the cement interpretation.
This work presents the culmination of technological excellence and technical expertise that helped clients to understand the condition of their cement better.