In CCS, CO2 is captured and then utilized in one of two ways: for EOR or for sequestration. The dominant CO2 approach in the medium to long term is expected to be sequestration, which is the injection of CO2 into characterized and appropriate geological formations deep below the surface. EOR is only applicable where suitable oilare present, and only for the limited time required to recover additional oil from the reservoir. Sequestration, on the other hand, is possible anywhere appropriate deep saline formations exist, which are geological formations far more prevalent and extensive than oil reservoirs.
The basics of geologic storage are known and it is practiced in specific and limited industrial situations, such as for acid gas disposition. The deployment of sequestration to mitigate climate change will however, require large scale implementation, the scale of which will be one or two orders of magnitude larger than existing industrial practice. Furthermore, it will mean that potential future sequestration locations might be closer to population centres than the few projects currently in operation.
Project Pioneer was to be one of the world's largest CCS implementations, serving to prove the technology, precisely quantifying its costs and demonstrating its safety and viability. The sequestration site was designed to permit the instantaneous injection of CO2 at a rate of 1.17 million tons per year (134 tonnes per hour) into the 1,800 m deep Nisku geological formation. In other words, the sequestration infrastructure and storage complex was to be able to accept the full output of the CCF. However, it was expected that most of the captured CO2 would be directed to EOR. Therefore, the planning basis was the sequestration by intermittent injection of up to 1 million tonnes of CO2 over 10 years, with most of the injection occurring in the first several years. Although injection was to be intermittent, the system was designed to always be available, subject to a reasonable ramp-up time.
Pioneer Storage Complex
Several past studies, including the Alberta SalineProject (ASAP) and the Wabamun Area Storage Project (WASP), had identified the 1,800 meter deep Nisku Formation in the Wabamun Lake area as a prospective reservoir for large-scale geologic sequestration of CO2 in a saline formation. The Nisku formation is an intermittently porous and tight dolomitized carbonate formation. It does not have major hydrocarbon production in the area and is the deepest stratigraphic unit with relatively extensive reservoir quality. The Winterburn storage complex, as defined by the Project, includes the Ireton, Nisku, Calmar, Blue Ridge, Graminia, Wabamun, and Exshaw formations. Underlying the Nisku formation is the Ireton formation, which is a regional shale that forms the bottom seal of the Winterburn storage complex. The interbedded shales and of the Calmar, Blue Ridge, and Graminia formations form the upper portion of the Winterburn Group and were expected to act as a primary seal for CO2 injection into the Nisku Formation. The Exshaw formation overlies the Wabamun Group and is a regional sealing shale able to serve as a secondary seal above the primary seal.Figure 5 provides an overview of the stratigraphic column in the Wabamun Lake area.
STRATIGRAPHIC COLUMN IN THE WABAMUN LAKE AREA
Geological Assessment Program
A full CO2 Storage Evaluation Program was undertaken and used to develop the scope of sequestration activities during the course of the 10-year injection period and a second 10-year closure period. The purpose of the Storage Evaluation Program was to evaluate the validity of potential geologic sequestration of CO2 in the Winterburn Storage Complex. Despite the completion of several other studies indicating that the Nisku formation in the Wabamun Lake area was likely suitable for large-scale geologic sequestration of CO2, sufficient information to support regulatory approvals for a CO2 storage scheme and a well-founded investment decision did not yet exist. The Program provided the necessary information to support both internal and regulatory decisions regarding the Project Pioneer CO2 sequestration scheme.
The Program involved evaluating the ability of the Winterburn storage complex in an area near the Keephills facility to provide sufficient injectivity, capacity, and containment to inject over a 10-year period and permanently store up to 1 million tonnes of CO2. The Program included the drilling and testing of one evaluation well, associated seismic acquisition, evaluating the integrity of existing wells in the Project area, and baseline environmental measurements. Water injection testing was completed in the evaluation well, but no CO2 injection tests were undertaken. A baseline three-dimensional (3D) seismic survey was planned but not initiated by the time of Project cancellation.
The evaluation well resulted in the acquisition of a large volume of high quality geological information:
- 45 m of caprock and reservoir core;
- Reservoir fluid samples;
- State of the art logs; and
- Injection test.
Photographs of core from the Nisku and Calmar formations are shown in Figure 6. The Nisku formation appears porous and vugular while the overlying Calmar seal is tight. Data was used to update the numerical geological model and support the development of a reservoir model to analyze CO2 injection and plume development scenarios.
PHOTOS OF CORES FROM THE EVALUATION WELL
The overall conclusion of the evaluation well program was the confirmation of very good storage formation and good caprock at the selected location. The evaluation well was determined to be capable of accepting the total Project Pioneer instantaneous injection rate of 1.17 million tonnes of CO2 per year.