Resurrection at AGL Silver Springs and Wallumbilla: case study of bringing field and surface facilities back to life

Abstract

AGL acquired the Silver Springs reserves and operations from Mosaic Oil in 2010, including several depleted yet condensate-rich gas fields. Gas was sent from Silver Springs to the Wallumbilla LPG plant (acquired by AGL in 2011) to be refined into sales gas, LPG and condensate. AGL’s objective was to build a commercial underground gas storage facility by converting the Silver Springs gas field into an underground storage reservoir. The business intent was to run the reservoir in alternating injection and withdrawal mode to take advantage of supply and demand economics. Setting up for injection and withdrawal required the commissioning of 10 petroleum producing wells, bi-directional high-pressure flowlines and associated infrastructure. A high-pressure injection compressor was commissioned. Injection of dry sales gas into wells commenced in 2011. Withdrawal at a higher rate than original was facilitated by new separation and dehydration equipment. The Wallumbilla plant was refitted extensively, including flare and venting upgrades and recertification of the pipeline and every pressure vessel on-site. Withdrawal mode operations commenced in October 2015. The LPG plant operability was demonstrated; however, running at design rate was compromised by excessive chilling in the cryogenic section of the Wallumbilla plant, caused by lower than expected LPG quantities in the withdrawn gas. Process engineering work resulted in design of a regenerative heater to warm the sub-cooled gas. The presentation covers the extent of the improvement work and the process investigations, which have formed the basis to ensure future versatile operation.