A Stabilizing Design: Changing Design Considerations for Condensate Stabilization on the Delta House FPS in the Gulf of Mexico

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FPSO Meeting seasonal RVP specifications Due to the seasonal changes in oil pipeline RVP specifications, the stabilization system design had to be flexible enough to meet requirements under various operating conditions. In the winter (April to September), the system would have to meet an RVP specification of 9.6psi absolute (psia). During these months, a higher concentration of C3, C4, and C5 could be pres- ent in the sales oil and the temperature setpoint for the reboiler could be relatively low (250°F) – resulting in higher oil produc- tion rates and a lower volume of natural gas liquids (NGL). It was estimated that approximately 16.5 bbl of stabilized conden- sate would be produced per every 1000 bbl of crude oil. In the summer months (April to September), a crude oil RVP specification of 8.6psia would have to be met. The stabilizer reboiler would operate at 315°F, which would allow for the maximum volume of stabilized condensate to be recombined with the crude before entering the sales line. In these condi- tions, the system would produce approximately 10 bbl of stabi- lized condensate per every 1000 bbl of crude oil. Additional design considerations Ambient temperatures also had to be considered when imple- menting the condensate stabilization system on Delta House. Outside temperature has a direct impact on aerial cooler outlet temperature, which in turn has an impact on the amount of condensate that feeds into the stabilizer, as well as the volume of NGL that's produced. Although the aerial process coolers on Delta House were designed to operate with 120°F outlet temperatures, LLOG and Audubon Engineering Solutions had to ensure that this setpoint could be maintained in the colder months of the year. Figure 2 shows early life system operation parameters during the summer and winter months. Because excessive volumes of water entering into the stabi- lizer could result in a number of costly issues, including the formation of a hydrate plug in the gas sales line, which can potentially force a total shutdown, freewater knockout and coalescence filters on Delta House were designed to remove as much water from the crude as possible. This was achieved by implementing a number of safeguards, including installing a water drain in the condensate stabilizer. Determining the presence of water was achieved by installing a sample loca- tion on the drain line, along with an interface level gauge and transmitter in the stabilizer overhead separator to alert opera- tors in the event that water begins to accumulate. Making Delta House a success The Delta House FPS achieved first oil in April 2015 – roughly two and a half years after construction on it officially began and two full years earlier than similar platforms around the globe. It has a capacity of 80,000 b/d of oil and 5.7 MMcm/d (200 MMcf/d) of gas and hosts production from multiple fields. The condensate stabilization system implemented by LLOG and Audubon Engineering Solutions on the FPS is just one example of the types of innovative methodologies that offshore producers are using to keep pace with the ever-present demand to optimize production facilities. With relatively modest space and weight requirements (75-80 metric tons, 22ft x 24ft x 47ft), the use of similar equipment on offshore platforms could become more prevalent as operators look for cost-effective ways to improve yields and ensure that their product meets pipeline owner specifications – especially in fields where reservoir studies indicate higher levels of condensate. Denis Taylor is a founder and managing partner at Audubon Companies. Taylor has over 25 years of engineering and project management experience in the oil and gas industry, including mechanical systems design and upstream and midstream consulting. His experience in the upstream industry includes the design and installa- tion of floating deepwater facilities and production platforms in coastal Louisiana and on the Gulf of Mexico's Outer Continental Shelf. Craig Mullett serves as offshore construc- tion manager for LLOG Exploration. Mullett has 35 years of experience in the engineer- ing, construction, and commissioning of offshore oil and gas facilities. Parameter Normal Sensitivity Summer Winter Summer Winter RVP [psia] 8.6 9.6 8.6 9.6 Cooler operationg temp [°F] 120 120 100 100 Advised reboiler operating temp [°F] 315 250 315 260 Freewater knockout feed ratio [BBL/1000 BBL crude] (Note 1) 32 39 33.5 44.5 NGL production ratio [BBL NGL/1000 BBL crude] 10 1.5 18 8.5 Stabilized condensate production ratio [BBL stab cond/1000 cond/BBL crude] 10 16.5 10 17.5 Note 1: Ratio reflects total liquids (water and hydrocarbons) feeding the freewater knockout. Fig. 2: Summary of early life operating conditions Eprinted and posted with permission to Audubon Companies from OE (Offshore Engineer) September © 2015 AtComedia LLC. For more information, contact us at

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