Credibility Assessment of Annular Casing Cement for P&A Campaigns: A Case Study in Campos Basin Offshore Brazil

Abstract

Abstract The assessment of annulus cement barriers is critical in well Plug and Abandonment (P&A) planning and execution. For wells with 10 to 30+ producing years, the data from well construction may be unavailable, incomplete, or not fully compliant with current industry good cementing practices. This case study presents a methodology for assessing qualification and credibility of annular hydraulic isolation, highlighting the challenges involved in the process. The engineering workflow starts by data mining from well construction regarding casing and cementing operations, drilling fluids, pumping schedule, wiper plugs events, casing centralization, washer, spacer, and cement slurry design in addition to anomalous events occurred. A mapping of the cement quality is then performed in representative wells which have availability of data with uniform criteria to establish key performance metrics. Finally, a novel statistical imputation methodology is then performed to overcome missing data followed by modeling and simulations, and a credibility analysis resulting in the qualification degree of the annulus cement – qualified permanent barrier, unqualified or failed. The methodology was applied for subsea wells in P&A campaigns in Campos Basin offshore Brazil, by using this credibility & criticality assessment in the B-annulus hydraulic isolation as an input for the P&A design and resulted in increased applicability of Through Tubing scope - without the necessity to remove the production tubing – and eliminated the need of additional evaluation of the production casing cement through logging tools or pressure testing. Consequently, a 5-day average reduction in P&A intervention was obtained. The analysis showed that the cementing strategies performed in well construction dates, despite different from current practices, provide sufficient cement quality in many scenarios. The studies conducted also show the correlation between cement evaluation logs and modeling of existing cement jobs with data imputation techniques to compensate for missing data in cement-job data. New methodologies and technologies for the assessment of annular isolation in wells to be plugged and abandoned are of relevant interest for the industry and taking in consideration the uncertainties and field experience into the qualification process of existing barriers is a challenge. This paper provides insight on how uncertainty levels may be reduced to still provide quantitative results and allow the selection of an optimized P&A design.