A Case of Achieving Sustainable Annular Sealing in a Deepwater Marginal Nigerian Field
The industry has been relying on cement as primary method for annular sealing. The initial evaluation considers a formation integrity test and a cement bond log. This shows good results in 85% of the cases and cement squeeze is the main remediation method. The ultimate measure of the sealing performance is production: more than 50% of the wells have sustained casing pressure in the B-annulus or are producing in degraded mode. Additional solutions are required to improve the sustainability of the industry.
The present paper discusses a case history in a marginal well in Nigerian deepwater. Primary cement evaluation was successful, in line with the industry statistic of 85% successful cases. However, production started with 60% Basic Sediments and Water (BS&W) and after six months of production, the well was shut-in due to excessive gas production. The investigation identified that the target Turonian oil sand was separated by thin shales from bottom water and gas cap.
In the sidetrack, two Well Annular Barrier (WAB) were used to augment the cement. The WAB is a metalexpandable packer that sets in open hole to assure sealing. One WAB was installed between the oil zone and the gas cap, and another one between the oil zone and the bottom water. The operation was successfully executed and the WABs expanded in wet cement after bumping the plug. Three years later, the well is still producing with 0.2% BS&W.
This paper discusses the well conditions that contributed to insufficient cement sealing, the WAB
application in the field, and the field results.
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