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The CO2 pipeline is 204.8 miles from Dakota Gas to the GoodWater Unit, which is part of Cenovus Energy's Weyburn oil field.Once the pipeline enters Canada it is known as the Souris Valley Pipeline for the area it passes through. Souris Valley Pipeline Ltd. is a wholly owned subsidiary of Dakota Gas. The North Dakota segment of the pipeline system begins with the 14" pipe heading west out of Dakota Gas, paralleling an existing power line corridor and various section line roads.
Near the town of Dunn Center, the route begins a northwesterly bearing. Near the crossing of Highway 22, the route assumes a northerly alignment as it passes east of the Killdeer Mountains and crosses the Little Missouri River. This northerly track continues for approximately 95 miles, crossing Lake Sakakawea at pipeline milepost 98, and passing just east of the town of Tioga, where a booster pump station is located.
The pipeline reduces to a nominal 12-inch diameter on the discharge side of the Tioga Booster Station. North of the town of McGregor, the route turns to the northwest, running approximately 20 miles, crossing Highway 5 between the towns of Noonan and Crosby. This northwesterly track continues until reaching the Saskatchewan border.
The Canadian portion of the pipeline crosses the border southwest of Estevan and takes a northerly track roughly parallel to the Souris River, until reaching the delivery point just north of the town of GoodWater. The pipeline was routed to provide a one thousand-foot buffer zone from centerline of the pipeline to any Canadian occupied residence, this exceeds both United States and Canadian requirements. In 2005, a second Canadian customer, Apache, was brought on-line.
The CO2 pipeline was designed to transport up to 240 mmscfd carbon dioxide on a continuous basis to the Tioga Station and continue with 160 mmscfd from Tioga to the GoodWater Unit. Beginning in 2000, the CO2 pipeline began to supply approximately 94 mmscfd of carbon dioxide to PanCanadian’s Weyburn Unit in Saskatchewan, Canada, for injection into their oil field. This injection process was expected to boost PanCanadian’s oil production from the current 14 Mbbl/d to a high of 34 Mbbl/d. Benefits of the carbon dioxide injection were expected to last for 12 to 14 years at 20 bb/d before production levels begin to drop.
Currently, with three compressor at Dakota Gas and a booster pump at Tioga, a total of approximately 150 mmscfd of CO2 is supplied to Cenovus Energy and Apache for use in Enhanced Oil Recovery (EOR).
The maximum allowable operating pressures (MAOP) for the pipelines are as follows:
|Line size & grade||MAOP||Hydrotest Pressure|
|14" OD x 0.375" WT Grade X70||2700 psig||3375 psig|
|12.75" OD x 0.375" WT Grade X70||2964 psig||3705 psig|
The CO2 pipeline was designed with 14" x 0.375"WT and 12.75" x 0.375"WT ERW pipe for general use, a minimum of 48" of ground cover was maintained for the length of the pipeline. At road crossings 0.500"WT SMLS Grade X65 heavy wall pipe was used for a minimum of one foot past the road right-of-way, a minimum of 5 feet of cover beneath the road and 4 feet of cover beneath the ditches was maintained. Railroad crossings required 0.625"WT SMLS X65 extra heavy wall pipe be used. All railroad crossings were bored with a minimum of 10 feet of cover allowing a minimum of 4 feet of cover in the ditches.
The Little Missouri River and Lake Sakakawea crossings were made with heavy-wall pipe the difference in the two crossings being that the pipe was buried and covered with rock on the Little Missouri and on Lake Sakakawea the pipe lays on the bottom and is buried only at the banks for 10 feet below the water line. The crossing of Jewel Creek in Canada was handled the same as the Little Missouri crossing.
All buried piping was coated with fusion bonded epoxy to prevent corrosion, in addition all piping used at bored crossings was overcoated with a abrasion resistant coating to prevent damage to the epoxy during installation.
To protect the pipeline from external corrosion a impressed current cathodic protection system is used. Cathodic protection on the CO2 pipeline is maintained by rectifiers located at MLV01, MLV03, MLV04, MLV05, MLV06, MLV07, Tioga Station, MLV08, MLV09 and MLV11. The cathodic protection is measured in voltage at test posts located at one-mile intervals over the length of the pipeline. We adjust the rectifier output to maintain voltage levels between .85 and 1.4 volts at each test station.
Activities on the pipeline fall basically into two categories, preventive maintenance and patrols. The exception to this is the locate request we receive from those folks wanting to excavate on our right-of-way or cross the pipeline. Once a locate request is received the pipeline staff locate and mark the pipeline, when the actual excavation or crossing is done it is supervised until completed by Dakota Gas personnel.