Sulfur Deposition Phenomena in Gas Systems and Lessons Learnt

Abstract

Abstract This study is aiming to conclude the root cause of elemental sulfur formation in the Gas handling facilities for an Oil field development facilities. The study focuses on supporting the concluded root cause by actual field trials. Practical short-term, midterm and long term solutions were studied and recommended including an optimization strategy to maximize utilization of existing facilities. The lessons learned for future projects were listed to overcome and manage the elemental sulfur formation issue. It was suspected that the root cause is related to potential oxidation of H2S due to the oxygen ingress associated with the generated nitrogen in the recycled low pressure gases. The study findings were achieved using actual field trials by either increasing the purity of the nitrogen source or by flaring (i.e. not recovering) the low pressure gases and monitoring changes in the operating conditions and the tendency of elemental Sulfur deposition for different N2 Purity levels. Accordingly, the mitigation measures were studied, assessed and the required modifications to overcome the problem are recommended. The first field trial was conducted considering flaring low pressure gases and increasing the nitrogen purity from 97 % to 99.8 %. The second field trial was conducted considering only increasing the nitrogen purity to 99.8% without flaring. For both field trials the tendency of Sulphur deposition was monitored in the Gas lift system and findings were recorded. The nitrogen purity was reduced gradually from 99.8 % to test implications on operation and note the nitrogen purity level at which Gas lift choke valves and Gas lift/ gas injection compressors are chocked by the elemental sulfur formation. According to the results of the field trials, the H2S oxidation due to the oxygen levels in the nitrogen stream was confirmed as the root cause for the elemental sulfur formation. All the lessons learnt to be considered at different stages of any project were captured and summarized in a typical checklist for the design of similar facilities at each project stage.