Abstract
During the recent economical growth period the lead time of stainless steel tubular reached in excess of a year. This was considered inadequate particularly for the completion of wells in some marginal reservoirs with short expected production capacities and life times. A systematic and comprehensive study was therefore, undertaken to select and optimize suitable materials for the completion of lower part of a number of gas producing wells. Key challenges included economy and appropriateness to allow a fitness for service choice of tubing material. The study covered two parallel elements including (i) corrosivity assessment and (ii) placement of downhole coupons and tubing string in the cemented part of the wells. This aided materials optimization by developing application domain diagrams (ADDs) for candidate materials including carbon steel (C-steel) and low carbon 3%Cr steels. Operational experience was captured through analysis of downhole corrosion coupons after six months of exposure to evaluate the in-situ system corrosivity. In addition, a limited number of wells were completed with 3 % Cr and carbon steel. After one year of production they were inspected by caliper runs showing encouraging results which led to additional wells being completed with C-steel. This paper summarizes the outcome of different studies and inspection and demonstrates the significance of correct materials selection approach and implementation of corrosion management strategy in meeting economy and appropriateness to enable fitness for service.
