Improving Well Integrity with Metal Expandable Technology in Abu Dhabi
When drilling in mature fields onshore in Abu Dhabi, a common challenge for the Abu Dhabi National Oil Company (ADNOC) presents itself when drilling through and attempting to cement depleted aquifer zones.
The current solution for this challenge uses top-down cement squeeze jobs from the surface that are only moderately effective. This solution often leaves approximately 5000 ft of inadequately cemented casing, which compromises well integrity over time.
In severe loss scenarios, because of the ineffective cementing, the aquifer water contacts the carbon steel of the casing. In the presence of oxygen, the reaction causes the well barrier envelope to corrode. As the well barrier envelope corrodes, significant HSE issues occur as personnel are exposed to subsurface fluids. HSE exposure requires workovers, so wells must be prematurely shut in, which defers production at great cost to ADNOC.
A more efficient, robust solution was needed, so ADNOC partnered with Welltec® to use the Welltec Annular Barrier (WAB®) with a two-stage cementing system in a series of pilot trials to determine the effectiveness of a metal expandable packer in preventing the corrosion occurring in numerous wells. These trials took place onshore in Abu Dhabi in the Bab field. The trial wells were slightly deviated oil producers.
A metal expandable annular sealing system is a reliable isolation mechanism for effective cementation behind aquifers because it provides high expansion in potentially washed-out wellbores and includes long, multi-element sealing systems with built-in redundancy. The two-stage cementing system operated by the inner string places cement above the metal expandable packer while maintaining casing integrity once closed. Additionally, the unique combination of these technologies provides a cost-effective life-of-well solution compared to current stage cementing methods.
The 1214WAB was selected for the trial, and the tools were mobilized to the well sites. The WABs were run in hole with a stage cementing port above.
With the casing at depth, the inner string cementing system was deployed. Once at depth, the primary cement job was pumped through the inner string. Following the primary cement job, the WAB inflated, and the cementing port was shifted open. Cement was pumped above the WAB back to the surface. The port was closed, and the toolstring was pulled out of the hole.
Following a successful execution of the two-stage cement job, cement bond logs were run to confirm zonal isolation. Log results revealed satisfactory isolation of the aquifer zones behind the 9-5/8” production casing. The pilot trials showed enhanced cement quality across the aquifer zones when compared to wells in similar conditions.
Additionally, this technology allowed conversion from a heavyweight casing design to a lightweight casing design. This conversion saved seven days of rig time and approximately $500k, representing 15% savings on well duration and 10% savings on well cost. Further, using the WAB in conjunction with inner string, two-stage cementing results in quicker deployment and well construction.
The true value of this solution, though, is realized in HSE. Avoiding well integrity issues cannot be quantified with time and cost savings. A robust well barrier prevents process safety events, and enhanced well integrity reduces the likelihood of production deferrals while enhancing profitability. For example, based on the data of one field alone from August 2018–May 2019, shut-in wells resulted in approximately one million barrels of lost production. The lost production is equivalent to approximately $30 million of lost value (assuming $30 per barrel of oil equivalent). Therefore, the value of designing and executing wells for lifecycle duration using metal expandable packer technology with inner string cementing presents huge value to ADNOC Onshore.