Optimization of Scale Treatment Program for Offshore Field Operations with Presence of Iron

Abstract

The presence of various levels of iron can be found in field brines primarily due to the mineralogy of the reservoir or from corrosion byproduct (Zhang 2015). The adverse effect of the presence of iron on the performance of scale inhibitors (SI) is known, and if left untreated, can lead to plugging of well tubing and pipelines. It can also cause fouling of separators; resulting in costly remediation and loss of production and revenues. For the asset under study, traces of carbonate scale and iron sulfide were detected throughout a topsides production system. It was suspected the carbon steel production tubing was corroding over time and the byproduct was reacting with hydrogen sulfide from the souring reservoir. There are a number of well-developed methods that can be implemented to treat corrosion, bacteria, and dissolve the iron sulfide downhole; however, none of these application methods were available for this production system. This paper will discuss the findings from laboratory testing for carbonate and sulfate scales in the precence of significant levels of iron. In order to select a proper scale inhibitor and the minimum effective concentration (MEC) for this system, a variety of chemistries were screened. Five scale inhibitors were selected for the testing, as shown in Table 1. The findings of the study show, Inhibitor D performed the best in the presence of iron at operationally viable dose rates in both static and dynamic testing conditions favorable for CaCO3, FeCO3, and BaSO4 precipitation. Table 1 Scale Inhibitor Chemistry Scale Inhibitor Chemistry A DTPMP − Diethylenetriamine penta(methylene phosphonic acid) B BHMT − Bis(Hexamethylene triamine penta) phosphonate scale inhibitor C AEEA − Ethylyethanolamine phosphonic acid E AMPS/AA − (2-methylpropanesulfonic acid and acrylic acid) copolymer based scale inhibitor F TEA − Triethanolamine phosphate ester