The Pointe-du-Lac reservoir is located approximately 100 km northeast of Montreal on the north shore of the St. Lawrence River, 12 km west of Trois-Rivières. The reservoir is oval shaped with the long axis oriented NE/SW. This depleted gas reservoir in an aquifer is primarily used for peak shaving. It is connected to the TQM Pipeline transportation system located 3 km north of the compressor station.
Nature of the site
The reservoir is composed of unconsolidated sand deposited after the next-to-last glaciation approximately 120,000 years ago. Its thickness ranges from several meters to more than 10 meters, and it is only 60 to 120 meters deep. The structure was created by the presence of a structural elevation in geological basement formations covered by glaciofluvial sand deposits with an impermeable clay layer serving as cap rock. The exceptionally high permeability and porosity of the sand makes the storage site ideal for peak shaving.
Thanks to the reservoir’s injection and withdrawal capacity, the working capacity can be cycled up to almost four times a year. It is recognized as one of the most shallow storage sites in operation. Its natural low pressure means that during withdrawal high compression is required in order to be able to inject into the gas network.
The following cut-away view shows the current Pointe-du-Lac site.
Due to its injection and withdrawal capacities, the site is used mainly for meeting the winter peak but can also be used for seasonal volumes. The following table shows the site’s specifications.
|Working capacity||36,600 103m3||1,3 Bcf|
|Max. withdrawal rate||1,600 103m3/j||56,5 MMcf/j|
|Max. injection rate||2,400 103m3/j||84,8 MMcf/j|
Because of a shallow storage area (approx. 70 m), pressure in the reservoir is low (740 to 250 kPa) and in particular much lower than the operating pressure of the pipeline it is connected to (7,000 kPa). This means that, unlike most of the world’s storage sites, the gas must be compressed during withdrawal and, conversely, pressure must be reduced prior to injection into the reservoir.
Injection begins with gas filtration and reheating. Next, the gas is initially decompressed to 1,500 kPa to feed the gathering system, and then decompressed a second time at each well prior to injection into the deposit.
The free water generated during withdrawal is separated from the gas by a separation module at each well. The wet gas from the wells is transferred to the compressor station via three compressor units, then dehydrated for transport through the gas system.