Corrosion Inhibitor Optimization for Sweet Corrosive Gas Field Based on Flow Assurance Study, Inspection Review and Assessment of Corrosion Erosion Likelihood

Abstract

Abstract Corrosion Inhibitor (CI) has been injected as corrosion mitigation supplementing corrosion allowance (CA) of Carbon Steel (CS) piping and pipelines at Mahakam since gas fields development in 1990's. By CI, the piping and pipeline integrity is expected reaching 20-30years design life. CI is considered effective not only by decreasing the CO2 or sweet corrosion likelihood. According to flow assurance study (FAS) focused on corrosion erosion as discussed in detailed by API RP 14E, CI presence increases the threshold of liquid erosional velocity. Disregard the possibility of CI absorption by sand, solid erosion is also managed by similar approach. Furthermore, thousands of CI injection package has been installed, monitored and maintained for decades with control valve limitation to set minimum injection rate as 2 liter/day. Considering production profile fluctuation, particularly when high amount of water and sand coming after plateau period, the CI forecast increase significantly, equal to the injection packages maintenance frequency and injection package problems. In 2020's, where reservoir depletion happened, the study to reevaluate the necessity of CI injection is initiated with objective to optimize (stop) CI injection at some flow lines thus preventing excessive CI consumption and process incompatibility issue without jeopardizing flow lines and pipeline integrity status. This paper summarizes the methodology up to getting >50% cost optimization, which covering assessment of natural corrosion likelihood (NCL) as per empirical CO2 corrosion model and API RP 14E, actual corrosion likelihood (ACL) from corrosion coupon (CC) and remaining life assessment (RLA) and fitness for service (FFS) assessment on flow lines inspection result as per process piping design code ASME B31.3, piping inspection code API 570 and when necessary FFS assessment code API 579.