Abstract
One of the major challenges of corrosion and scaling management in sour gas wells is to effectively monitor corrosion and scaling under real-flow regime conditions. It is very difficult to simulate the actual environment and flow conditions in laboratory experiments to study downhole corrosion and scale formation. Understanding the corrosion and scaling mechanism under downhole conditions is very important in order to develop effective prevention and mitigation strategies in a timely manner.
An advanced downhole corrosion and scale monitoring (DCSM) tool has been designed and developed to monitor corrosion and scale formation in sour gas wells. This monitoring system represents significant improvements over the current industrial technology by directly measuring corrosion and scale deposition in real downhole conditions using exchangeable coupons with identical metallurgy as the downhole completion tubing. A slick line with a retrievable high-expansion gauge hanger was used to deploy and anchor the DCSM downhole at the desired depth. The tool was retrieved after 3 months exposure to the reservoir conditions for post-laboratory analysis. Advanced analytical techniques were carried out to understand the corrosion and scaling mechanism, including SEM, EDS, XRD, and surface profile measurement besides quantifying the weight changes.
The results showed that a thin layer (~3-4 μm in thickness) of iron sulfide scale was deposited on the surface of coupon. It served as a protective layer to prevent and reduce further corrosion and scale buildup. To understand the mechanisms of scaling, the surface scale deposit was removed by corrosion inhibited acidic solution. The surface profile measurement showed localized pitting corrosion which appeared on the surface of coupon, which indicates that corrosion happened first followed by scale layer deposition on metal coupon surface.
The newly developed DCSM tool has an advanced design which allows direct corrosion and scaling monitoring under downhole conditions. Post-laboratory analysis on retrieved coupons can provide corrosion and scaling mechanism for specific metallurgy under real downhole conditions. Proper corrosion and scale management programs could be designed to minimize the effects of corrosive gases. The developed tool can be used to monitor the effectiveness of the corrosion treatment and can be deployed in sweet gas wells, oil wells and water supplier wells.
