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Customer Profile: Process Ecology is an oil and gas consultancy, based in Calgary, Canada, assisting companies in the operation of their production, gas processing and pipeline facilities. The company provides solutions for many operations in the oil and gas industry - including gas plant rating, debottlenecking, flare system analysis, heat recovery, environmental compliance and optimization.
Background and Challenge: As natural gas is transported through pipelines, associated condensation occurring in the pipeline may result in liquid slug formation. Slugging refers to varying or irregular flows of gas and liquids (or liquid surges) in pipelines. Severe slugging can result in plant shutdowns, unwanted flaring, and reduced operating capacity. Hence, companies are investing money and effort to overcome this problem by installing slug catchers to “catch” the slugs before they reach their destinations at gas treatment facilities, and prevent disruption of downstream operations.
There are three types of slugging:
- Terrain-induced slugging caused by changes in elevation
- Hydrodynamic slugging caused by the formation of waves on the liquid surface as a result of the faster moving gas
- Pig-induced slugging caused by pigging operations in the pipeline used to push liquid contents to the outlet
The company wanted to install slug catchers that are optimally sized to minimize CAPEX. By accurately predicting slugging volumes and durations, engineers can anticipate slug catcher volumes. A slug catcher which is too large will waste resources, while a slug catcher that is too small risks downtime due to the disturbances that slugs might cause in gas processing operations. After assessing the available options, Process Ecology zeroed in on the solutions provided by AspenTech.
The Solution: Utilizing the entire aspenONE Engineering suite, Process Ecology developed a solution for predicting the volume and duration of terrain, hydrodynamic and pig-induced slugs to adequately predict the size of the slug catchers needed to manage the impact of slugs when they reach gas processing facilities. The Aspen HYSYS pipe segment slug analysis tool was used to predict the potential for hydrodynamic slugging. Aspen Hydraulics, a tool available in Aspen HYSYS Upstream, was used to determine terrain-induced slugging using an elevation profile and slug prediction tools built into Aspen Hydraulics. Finally, the company used liquid holdup and the dynamic mode in Aspen Hydraulics to predict pig-induced slugging. As expected, the results were highly sensitive to the composition of the heavy ends of the natural gas being transported. The company also found that by using client predictions for the composition, a slug catcher with a volume of only 1000 bbl (oil barrel) was needed. This is one third the conservative estimate of 3000 bbl that the operator had assumed, thereby saved significant capital costs while ensuring optimal production.
Quantifiable Benefits: The company saved substantial capital costs by properly sizing equipment in gas gathering systems – in this case 60 percent. Additionally, it gained insight into pipe flow and prevented downtime in gas production, which has tight revenue margins; the solution enabled them to predict process constraints and understand the process sensitivity with respect to feed composition.
With Aspen HYSYS and Aspen HYSYS Upstream, companies like Process Ecology can simulate a wide range of oil and gas processes and ensure that they find accurate solutions for compliance and sustainability. This is broadly applicable to a wide range of oil and gas field expansion and optimization situations, especially in today’s environment where break even cost of production must be reduced.
Keywords: AspenTech, Aspen HYSYS, Process Ecology, Oil & Gas, Slug Catchers, ARC Advisory Group.