Novel Approaches to Sour Gas Treatment in Oil and Gas - Onshore and Offshore Facilities

Abstract

Abstract The objective of this paper was to investigate novel approaches to sour gas treatment for use in the Middle East that are outside the common oil and gas market and compare them to more traditional techniques. The methods employed in this paper were based on one central tenet – delivering to the client a practicable, economical solution to producing from an extremely sour (> 40,000 ppm) gas field. The target H2S / SO2 emission limit of the system was 125 ppm / 300 mg/Nm3. A gated process was used whereby the scope was split to include SWOT (Strength, Weakness, Opportunity, Threat) analysis between the Feasibility Analysis and Concept Select stages to narrow down what could viably be implemented onsite - whether subsea, offshore or onshore. The procedure by which technologies were identified was to contact vendors from different sectors to find a suitable candidate for sweetening such a sour field. Initial observations were that the traditional crutch of offshore gas sweetening in the O&G sector – H2S scavengers, typically Triazine – were too inefficient for the volume of H2S. Non-Regenerative and Regenerative adsorbents were also investigated. These were found to be low CAPEX but high OPEX and high CAPEX but reduced OPEX respectively due to the nature of the technologies. Both were found to be unsuitable on economic grounds. Membranes were then approached as an offshore solution. Without the need for large chemical inventories, membranes were a promising candidate due to reduced risk. Unfortunately, the large contact area requirement was too much for the offshore platform. Moving onshore, Claus units are the typical method of sulphate disposal. These were investigated alongside Liquid REDOX, Iron Chelate, Biological Processes and Modified Tail Gas Treatment Units (TGTU’s). From these it was found that the Modified TGTU was economically viable, could be implemented onsite and tied in to existing infrastructure with minimal CAPEX or OPEX. The Modified TGTU process produced fertiliser from SO2, a saleable product which offset the cost of implementation and was more valuable than products from traditional Claus units. The Modified TGTU unit was sourced from coal plants in Asia and had not been deployed for Oil and Gas use. By going outside our common areas, we found something that was a huge benefit to the client by providing a safe, clean operable and efficient method of gas sweetening.