Abstract
Abstract
Based on the history of cementation of 9-5/8″ heavy casing design in NEB field, all the wells are cemented with lead (10.0 ppg – 12.7 ppg) and tail (15.8 ppg), where during the cementation pure cement is gained in surface. Based on the Cement log, the lower area (Tail) is accepted and some discrepancies in the interpretation on the upper section due to tools limited capability in reading light weight cement and presence of dual casings. However, several years after the completion some of the wells have been identified as SAP B (Sustain Annulus Pressure) between annulus 9-5/8″ casing and 13-3/8″ casing.
An advance logging tools was run to one of the recent SAP B wells, that used integrated approach to do interpretation that considers the data from 3-dimensional acoustic sensors, cement bond logs, production data, open hole data logs and recent well operations. The interpretation is most likely scenario for this SAP B is micro-debonding of 9-5/8″ casing to cement which is causing the gas flow to surface; and cement failure below 13-3/8″ shoe with the source of SAP B is in Fiqa formation, while all the formations below Fiqa are acoustically quiet and no annular flow is happening from deeper reservoirs.
As per standard practice, in such situation the SAP B must be cured prior to re-complete the wells. To cure the SAP B, section milled across aquifer (RUS and Dammam) will be performed, followed by plug and squeeze across the milled section and later will be run with 7″ tie back cementation to surface. Performing these steps will require minimum 5 days prior to re-run completion string.
To improve well integrity in annulus between 9-5/8″ casing and 13-3/8″ casing, a dependable barrier for long term well integrity should be provided. A novel approach involving single cement slurry modification with expansion properties was discussed by adding post set crystalline material into cement design and tailored it to have expansion effect to minimize micro debonding and micro channeling. In parallel, maintaining slurry fluid loss properties is also critical to provide better cement bond. By changing the cement design into single slurry, the potential of losses will rise during cementation and might end up with poor zonal isolation in the annulus. Other aspect taking part as consideration is by using adequate spacer volume with engineered rheological properties for better cleaning, maximize both centralization and pump rate since pipe movement (rotation and/or reciprocation) is not an option.
The job was planned to be performed in single stage cementation, with maximize the centralization profile, use sufficient volume of spacer, then followed with pumping single slurry expandable considering adequate excess of open hole and displacing with maximum rate using the rig pump for better displacement efficiency.