Completion Tubing Optimization: Meeting the Challenge Through Prediction and Operational Experience

In the current economic climate, correct and appropriate selection of materials and corrosion management strategy are becoming increasingly more imperative.  A systematic and comprehensive study was undertaken to select and optimise suitable materials for the completion of lower parts 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.

Corrosivity assessment was carried out through characterising the production scenarios into several generic operating clusters combining water chemistry, production parameters and effluent characteristics.  The information was taken to assess system corrosivity by using CORPLUS prediction program.  This aided materials optimisation by developing widows of application for candidate materials including carbon and low carbon 3%Cr steels.  The windows were aligned to past operational successes and made recommendations for the use of these alloys for different production clusters. 

Operational experience was captured through placement of downhole corrosion coupons for six months to evaluate the in-situ system corrosivity.  In addition, a limited numbers of wells were completed with 3 % Cr and carbon steel.  After one year of production they were inspected by calliper runs.  Both calliper runs and downhole coupons showed encouraging results.  This led to additional wells being completed with carbon steel which were inspected after one year with no adverse sign.  At present some 50 wells are completed with carbon steel and 3% Cr and the feedback are positive.

This paper demonstrates clearly the significance of correct materials selection approach and implementation of corrosion management strategy in meeting economy and appropriateness to enable fitness for service.  Significant and unique operational experience is shared to allow tubing selection for similar producing scenarios.