Internal Pipeline Corrosion Study on the Changes From Oil to Gas Production

Abstract

Abstract The switch from oil to gas production will dramatically change the operation conditions in the producing wells, topside facilities, and transportation pipelines. Besides the changes in gas/liquid compositions, operating pressure and temperature, multiphase flow in the pipeline will also shift from a high-liquid load pattern to a low-liquid load pattern. Typically, the demarcation point between the two patterns could be considered as GOR of 1000 SCF/BBL. Forecast of the field studied in the paper indicates that the transition might happen after a few years and GOR will increase gradually with the aging of the wells. The changes will have a great impact on internal pipeline corrosion and corrosion inhibition and thus require a systematical study to identify the keys parameters and strategize a suitable corrosion management plan. In this paper, the experiences gained from current corrosion monitoring and corrosion inhibition programs were reviewed first. Corrosion scenarios were also analyzed for future operational conditions by conducting both fluid- dynamic analysis and corrosion risk prediction along the pipeline for a wet gas environment. In order to study the impact of flow on the corrosion inhibitor application, laboratory tests were carried out to evaluate the incumbent corrosion inhibitor for future wet gas environment. The lab study focused on testing the partitioning capability of the corrosion inhibitor at different water cuts (10% – 100% water cut) and the localized corrosion risk due to the high shear stress using both rotating cylinder electrode (RCE) apparatus and rotating cage type of autoclave. The study showed that, though the corrosion risk of the system was determined to be relatively low, the option of applying corrosion inhibitor by batch treatment should be ruled out due to the possible breakdown of inhibitor film in a turbulent flow, which is associated with high shear stress and subject to gas bubble impingement. Lab tests also indicated that continuous treatment of 25 to 50 ppm corrosion inhibitor could minimize the localized corrosion risk of carbon steel pipeline in a 150-Pa shear stress flow.