Brine Storage Pond- Storage of Natural Gas Liquids in Salt Caverns
Location: Sarnia, Ontario, Canada Timeframe: Nov 2012- Dec 2012 May 2013
Scope of Work: Supply and Install 120,000 SQM of Enviro Liner 6040HD, 65,000 SQM of Geonet -5, 65,000 SQM of LP12 non woven geotextile and 40,000 SQM of LP200 woven geotextile: - Double Lined Brine Storage Pond - Leak Detection and Monitoring Project Partners: Pembina Pipelines SNC Lavalin
Situation and Background Information
Pembina Pipelines operates transportation and storage infrastructure delivering oil and natural gas across North America with network of pipelines and rail transport. At their Sarnia location, 9 salt caverns are in service and they are looking at significant expansion potential for their underground storage of Natural Gas Liquids (NGLs). A schematic of “Salt Cavern” is shown in Figure 1.1
Demand for NGL’s is often higher during the winter, partly because it is a heating fuel in residential and commercial applications. NGL’s are stored underground and extracted during winter months to meet the heavy demand of consumers. One way of underground storage of NGL is within “Salt Caverns”, which provides many benefits compared to other high pressure aboveground storage methods.
Discussing benefits of different storage systems is beyond the scope of this document. Salt caverns are manmade features constructed within deep salt bed deposits. The caverns are used to store hydrocarbons and liquefied petrochemicals like NGL’s. A 'salt cavern' is constructed by dissolving the salt deposits underground and extracting the brine solution into a holding pond, this leaves a large empty space in the formation.
These brine storage ponds need to be lined to prevent leakage and potential contamination of aquifers. Brine storage ponds are primarily double lined systems that comprise of a Geosynthetic drainage layer encapsulated between two layers of Geomembrane. The drainage layer monitors and captures any leaks from the primary Geomembrane.
There were a series of challenges during the design phase from selection of materials to method of deployment i.e.evaluating benefits of shop fabrication over field fabrication. Some of these challenges are listed below:
- Chemical resistance of the material
· long term compatibility of saturated brine to Enviro Liner 6040HD
- UV resistance of the material
· long term UV weathering resistance of Enviro Liner 6000HD in an exposed application
- Drainage performance of the Geonet
· transmissivity of a Geonet compared to Geocomposite
- Compressive resistance of a 40 mil (1.00 mm) Enviro Liner 6040HD at normal than higher hydrostatic loads
· testing to determine if a 40 mil Enviro Liner 6040HD will deflect into the cells of the Geonet
- Dealing with weather conditions
o due to higher than average rainfall in fall 2012, site was completely saturated
- Meeting the strict timeline
· owner wanted the pond to be operational in Spring 2013
Solution and Results
Chemical and UV Resistance: Layfield has performed extensive salt solution testing at elevated temperatures at laboratories in both Canada and Australia. The results show excellent resistance of Enviro Liner 6040HD to brine at elevated temperatures. Enviro Liner 6040HD is a fortified Geomembrane and is formulated with prime grade resins and high loading of anti-oxidants that provides excellent UV and chemical resistance in a long term exposed application. This provides the owner and engineers the comfort of choosing a lining material that is tested to field conditions and is backed by testing and research. Figure 2 show effect of temperature on tensile strengths, it is evident from the results that Enviro Liner 6040HD has limited or no effect after exposure to brine at elevated temperatures.
The weathering performance of Enviro Liner 6040HD is backed by our 30,000 hrs. of accelerated UV testing and increased High Pressure Oxidative Induction Time (HPOIT). HPOIT values indicate the performance of
Transmissivity of Geonet to a Geocomposite: Available data from the manufacturer show that a Geonet’s transmissivity is 20 times better than that of a Geocomposite. A geocomposite has a geotextile attached to the geonet. Initial designs were considered using Geocomposite since a 40 mil Geomembrane was considered for this application. In general, the hypothesis was that the 40 mil (1.00 mm) Geomembrane may deform or deflect into the cells of a Geonet or could even puncture the membrane at the places where seams of geonet will overlap, as shown in the picture below. The hypothesis was proven wide of the mark as the tests from our compression study showed non-detectable deflections of the Geomembrane from its plane. The Geonet instead of a Geocomposite encapsulated between layers of Geomembrane ensured better drainage performance in this specific application.
Compression Testing Study: To determine compression resistance of a Geomembrane to higher hydrostatic loading, Layfield performed a series of tests to measure the deflection a Geomembrane into the Geonet. The results clearly indicate that Enviro Liner 6040HD, 40 mil Geomembrane when exposed to 25 PSI (172 kPa)(Equivalent of approximately 60’ of water head) shows non-detectable deflections/deformations.
There was heavy rainfall during fall 2012 season and the site was completely saturated. Layfield proposed using prefabricated liners to minimize the field welding component ensuring that the liner installation was as per schedule. Shop fabrication involves assembling roll stock Geomembranes in large panels in a controlled environment. The seam quality is not affected due to weather elements and efficiency of seaming in a shop environment is higher than what can be achieved in the field. The majority of the installation was carried out between Nov-Dec 2012. Due to site conditions, as seen in figure the installation was postponed until late April.The installation was completed early May 2013.
To help reduce installation time and construction costs, a 40 mil (1.00 mm) Enviro Liner 6040HD geomembrane was recommended by the engineering firm to contain saturated brine solution in this large exposed double lined containment application. Enviro Liner 6040HD is a premier grade flexible geomembrane alloy that has several advantages over commodity grade field installed liners. Enviro Liner 6000HD has excellent tensile elongation and multi axial properties and long term UV weathering properties. It is also a highly flexible material which can be factory prefabricated improving welding seam integrity while reducing the quantity and field welding by up to 75%.Enviro Liner 6000HD offers very good resistance to brine fluids and is not subject to environmental stress cracking. In conclusion, this was a very successful project which fully met the Owners requirements being completed on time and on budget without operational problems.Layfield is a leading manufacturer and supplier of flexible geomembranes designed for Oil & Gas upstream, midstream and downstream operations. Visit Layfield at www.layfieldgroup.com for further information on our geomembrane technology and services.