Large-Scale Acid Gas Injection Facilities for Gas Disposal
Authors: Kenefake Daryl , Hawrysz Daniel , Al-Mohannadi Ahmad 
Published: February 2016

Acid Gas Injection (AGI) has commenced at both Ras Laffan LNG Company Limited's RasGas complex (RasGas AGI) within the Ras Lafan Industrial City, Qatar and at ExxonMobil Production Company's LaBarge Treating Facility (LaBarge AGI) in southwestern Wyoming, United States. Acid gases, nominally consisting of hydrogen sulfide (H2S) and carbon dioxide (CO2), are naturally occurring, non-hydrocarbon gases that can be associated with oil and gas production. The successful commissioning, startup, and operation of these facilities demonstrate feasibility and safe operability of AGI technology to dispose of waste gases on a large scale.

Safety is a core value for RasGas and ExxonMobil and should be a core value for any operator intending to install AGI facilities. These AGI facilities are designed to meet or exceed relevant industry standards and have stringent requirements for operating and maintenance procedures, operator training, and emergency response planning. The safe operation of an AGI facility requires the integration of engineering design, commissioning, operating and maintenance practices, and emergency response planning.

This paper discusses the lessons learned through the implementation of AGI for these two facilities, RasGas AGI and LaBarge AGI. This paper focuses on the issues associated with acid gas injection facilities relative to industry experience with lower pressure H2S operations. The discussion includes the impact of AGI on design, commissioning, and operations and maintenance for these facilities, including important safety considerations and key lessons learned during commissioning, startup, and initial operation and maintenance.

This paper has been prepared for presentation at the International Petroleum Technology Conference (IPTC) in Dubai, UAE scheduled for December 3–6, 2007.

BACKGROUND

There are approximately 80 AGI facilities operating throughout the world. Most of these have capacities less than 5 MMCFD and utilize reciprocating compressors discharging directly into injection wells. Both the RasGas AGI and the LaBarge AGI facilities started injection in 2005 and are considered world scale in terms of H2S concentration, pressures, and volume of acid gas injected.

Both of these facilities have centrifugal compressors, coolers, separation equipment, pipelines, and injection wells to dehydrate, compress, and inject acid gas. Additionally, the LaBarge AGI facility has liquefaction facilities and pumps to achieve pressures needed for injection. Key surface technologies include acid gas dehydration that aids corrosion control and hydrate prevention, acid gas liquefaction, and acid gas pumping.

Ras Laffan Liquefied Natural Gas Company Limited II is a joint venture company formed in 2001 between Qatar Petroleum and ExxonMobil. The venture encompasses production operations from Qatar's giant North Field for the manufacture of Liquefied Natural Gas (LNG) from RasGas Trains 3, 4, and 5 which it exports to consumer markets. The RasGas AGI system supports this operation and the Al Kaleej Gas Phase 1 facilities. The RasGas AGI facility is designed to inject 88 million standard cubic feet (MMCFD) (93,700 Nm3/hr) of acid gas at pressures up to 1,650 psig (114 barg). The source gas for the RasGas AGI facility is from the activated MDEA and Selexol systems and consists of water saturated acid gas with 25% H2S, 73% CO2, and &lt;2% mercaptans. No additional treating systems are used to condition the feed gas streams. Actual operating conditions have not required full use of this design capacity. The RasGas AGI facilities include three four-stage acid gas centrifugal compressors, and inter-stage cooling for compression is accomplished by a dedicated cooling water system. Acid gas is compressed from 7.5 psig (.5 barg) to 1650 psig (114 barg) and is in dense phase conditions, under-saturated with water, at the 4th stage compressor discharge pressure.