The HPCSS in-situ method injects high-pressure wet steam into the reservoir for several weeks. Once filled, the reservoir is left to “soak” for several weeks. The heat softens the bitumen and the water dilutes and separates the bitumen from the sand. The pressure creates cracks and openings through which the bitumen can flow back into the steam injector wells. In the ensuing production phase, the bitumen is pumped up the same well through which the steam was injected. Source: CNRL. Click to enlarge.

HPCSS involves injecting high-pressure steam into a reservoir over a prolonged period of time. As heat softens the bitumen and water dilutes and separates the bitumen from the sand, the pressure creates cracks and openings through which the bitumen can flow back into the steam-injector wells.

HPCSS uses a single well bore to inject steam and produce bitumen. This technology has been historically applied to reservoirs that have barriers to vertical flow, CNRL noted. Production peaks and troughs at Primrose have been a reflection of the cyclic steam process—the peaks are associated with production cycles from newer, less mature wells and the troughs are associated with production cycles from the more mature areas in the field.

HPCSS differs from steam assisted gravity drainage (SAGD) operations where steam is injected at lower pressures without fracturing the reservoir and uses gravity drainage as the primary recovery mechanism.

While HPCSS requires only the one well bore (as opposed to two with SAGD), and is adaptable to thinner inter-bedded reservoirs, it also has a lower recovery factor than SAGD, CNRL says.

The latest report from the AER on 16 August also noted that 397 m³ of oily vegetation has been removed from one site; and 5,096.66 tonnes of impacted soils have been removed from the three others. 20.7 hectares total (51 acres) is reported to have been impacted by all four sites.

On 24 June, AER received reports of an unnamed standing body of water impacted by bitumen coming to the surface from underground source. AER began working with CRNL to determine the cause, control the release, and establish containment.

AER subsequently ordered CNRL to suspend its HPCSS operations within the Primrose East section of the project area. In response to a more recent incident at Primrose South, AER ordered CNRL to take further measures, including suspending the steaming operations within one kilometer of the Primrose South incident and restricting steam operations throughout Primrose North and South.

These restrictions will remain in place until the cause of the releases has been confirmed, CNRL can introduce operating practices to minimize the risk of similar events occurring, and full approval has been granted by the AER.

By mid-July, with the seepage ongoing, AER directed CNRL to undertake the following actions:

1. To accelerate efforts to contain and clean up the bitumen-emulsion release and submit detailed containment, cleanup, and remediation plans to the AER and Alberta Environment and Sustainable Resource Development (ESRD) by 29 July.

2. To develop and implement a plan, subject to AER approval, to ensure all bitumen emulsion releases to surface within the project area have been identified and, if identified, appropriately addressed to the AER's satisfaction.

2009 incident. The current event is not the first report of surface seepage of bitumen in the Primrose project. On 3 January 2009, a surface release of bitumen emulsion was discovered in Primrose East.

On discovering the bitumen emulsion, CNRL shut in all steam injection at Primrose East and initiated emergency flowback to depressurize the formation. Approximately 11,380 tonnes of solids (including snow, organic material, soil, and bitumen) was ultimately removed from the site for landfill disposal, and 904 m³ (238,812 gallons US) of bitumen was recovered.

A static investigation was performed, but findings were largely inconclusive. As a result, CNRL applied for and received Energy Resources Conservation Board (ERCB) approval to conduct limited diagnostic steam injection with enhanced monitoring at Primrose East to try to identify the bitumen emulsion release pathway. (ERCB was the predecessor organization to the AER.) Diagnostic steam injection did not reactivate the release pathway. However, the ERCB held the view that the successful steaming at more traditional PAW steam volumes without incident showed that HPCSS could be safely conducted at Primrose East.

In February 2011, CNRL submitted its Final Investigation Report, which included the results of the 2009 static investigation, supplemental filings, and the results of the dynamic investigation that took place from August 2009 to March 2010. CNRL concluded that a general pattern of the bitumen emulsion flow path to surface could be inferred, but that a detailed flow path could not be determined with certainty.

The ERCB agreed that the bitumen emulsion pathway could not be identified with certainty based on the available data. However, the ERCB is of the view that the shale was likely breached by high-pressure steam injection not related to a wellbore issue, that the Grand Rapids Formation water sands did not act as a diverter, and that a pathway found through the Colorado Group likely involved a wellbore or a series of pre-existing faults.

In its report, ECRB noted that the steam volume injected in Cycle 1 at Primrose East was significantly higher on a pore volume basis than in past HPCSS operations due to reduced well spacing. The ERCB said that this likely contributed to the bitumen emulsion surface release. CNRL acknowledged that the Cycle 1 injection volumes may have contributed to the release.

The ERCB is also of the view that geological weaknesses in combination with stresses induced by high-pressure steam injection may have contributed to the release. The geological weakness may be caused by deposition, subsequent erosion, or stressing along the salt collapse edge at Primrose East.

As a result of that incident, the ERCB put limits on the steam injection volumes that CNRL is allowed to inject per cycle.

Resources

• Canadian Natural Resources Ltd. Primrose East Bitumen Emulsion Release January 3, 2009 (ERCB Investigation Report 8 January 2013)