Inadequate Wellbore Cleaning Leads to Poor Cement Bond

The cement bond log (CBL) and variable density log (VDL) performed during the initial well completion indicated nil to poor cement around the 9 5/8-inch casing across both stages of cementing. This poor cement bond was partly attributed to inadequate wellbore cleaning before the cementing process. The wellbore was not properly cleaned of drilling mud, cuttings, or other debris, which can interfere with the cement’s ability to bond effectively to both the casing and the formation.

Casing Failure: There was potential for casing failure due to the lack of support from the cement, which could not properly isolate zones or support the casing against the wellbore. Hydrogen Sulfide (H2S) Leakage: The failure facilitated the leakage of H2S water from the Paleocene formation into the wellbore, indicating a loss of zonal isolation. This was evident during well reentry operations where pressure in the well could not be maintained. Operational Disruptions: The well required extensive repair work, including running a 7-inch tie-back string to restore integrity, which involved additional costs and time.

The response included scraping and cleaning the wellbore, running new casing, and cementing it in place with a careful approach to ensure better cement placement and bond. This involved using lightweight cement lead slurry followed by a heavier tail slurry to achieve better cement distribution and bonding.