Abstract
This paper demonstrates a successful practice on how to optimize centralizer placement through analyzing the measured casing standoff by an enhanced ultrasonic imaging tool in one underground gas storage (UGS) project in west China.
In the initial phase of the project, it was found that the cementing bonding in the dual casing section was commonly unsatisfactory in the production liner cementing. Factors that affect cementing quality, including fluid density/rheology hierarchy, pumped fluid volume, and pumping rate, were verified and excluded from consideration as possible causes for the bad bonding. With the measured casing standoff from one ultrasonic imaging tool, acentric casing resulting in bad mud removal was identified as the root cause. Centralizer placement was optimized with a specialized software simulation and, as a result, the subsequent drilled wells were cemented with excellent quality.
The imaging tool combines conventional ultrasonic pulse-echo techniques and flexural waveform attenuation measurement. Real casing standoff can be computed based on third-interface echo measurement. With the measured standoff, engineers can re-evaluate the original centralizer design and analyze whether there is a relationship between unsatisfied standoff and poor cement bonding, on basis of which engineers can improve centralizer placement for the following jobs to achieve better cementing quality.
Previously, engineers did not have a way to realistically evaluate their centralizer designs as the standoff results could only be simulated virtually. By adopting this new imaging tool, a new approach in the cementing design, execution, and evaluation cycle is established, which is proven to be an effective method to enhance cementing quality in the UGS project.
