|
Project Summary |
The location of the project is the Weyburn oilfield, first discovered in 1954. It covers and area of some 52,000 acres and has a current oil production rate of ~3,067 m3/day. This comes from a total of 963 active wells made up of 534 vertical wells, 138 horizontal wells, and 171 injection systems. There are also 146 abandoned wells. Current production consists primarily of medium-gravity crude oil with a low gas-to-oil ratio.
In October 2000, EnCana began injecting significant amounts of carbon dioxide into a Williston Basin oilfield (Weyburn) in order to boost oil production. EnCana is operator of the oilfield and holds the largest share of the 37 current partners. Initial CO2 injection rates amounted to ~5,000 tonnes or 95 million scf/day (2.7 million m3/d); this would otherwise have been vented to the atmosphere. Overall, it is anticipated that some 20 Mt of carbon dioxide will be permanently sequestered over the lifespan of the project. The gas is being supplied via a 205 mile long pipeline (costing 100 million US$) from the lignite-fired Dakota Gasification Company synfuels plant site in North Dakota. The company is a subsidiary of Basin Electric Power Co-operative. EnCana is taking ~40% of the synfuels plant’s capacity. At the plant, CO2 is produced from a Rectisol unit in the gas cleanup train. The CO2 project adds about $30 million of gross revenue to the gasification plant’s cash flow each year.
This is the first instance of cross-border transfer of CO2 from the USA to Canada. Whilst there are emissions trading projects being developed within countries such as Canada, the Weyburn project is essentially the first international project where physical quantities of CO2 are being traded for purposes of minimising climate change.
Another key feature of the project is that the CO2 comes from fossil fuel use. As of 2008, there were 100 CO2-EOR projects, however, most of these rely on naturally-occurring sources of CO2. Thus, the Weyburn project represents a significant increase in the use of anthropogenic CO2 in EOR projects in both the USA and Canada. It is estimated that 50% of the injected CO2 will be permanently sequestered in the oil that remains in the ground, the remainder coming to the surface with the produced oil. From here, it is being recovered, compressed and reinjected.
During its life, the Weyburn project is expected to produce at least 122 million barrels of incremental oil, through miscible or near-miscible displacement with CO2, from a field that has already produced 335 million barrels since its discovery in 1955. This will extend the life of the Weyburn field by approximately 20-25 years. It is estimated that ultimate oil recovery will increase to 34%. CO2 sequestration carried out on the scale of the Weyburn Enhanced Oil Recovery Project is potentially a low-cost, practical and long-term management option for national and international carbon dioxide emissions.
It has been estimated that, on a full life-cycle basis, the oil produced at Weyburn by CO2 EOR will release only two-thirds as much CO2 to the atmosphere compared to oil produced using conventional technology. The level of effectiveness of this technology makes it an attractive option for reducing national levels of CO2 emitted. Many of the oil fields in the Williston Basin, and indeed, other sedimentary basins throughout the world, could capitalise on the EOR techniques in use at Weyburn, substantially increasing the levels of CO2 that could be sequestered in this way.
In operation, two large compressors are used to transport CO2 through the pipeline. During normal operations, CO2 is transported in the pipeline in a gaseous form, but in a supercritical state; this means that it behaves much like a liquid. During the pipe-filling process, the CO2 remains in a gaseous state, however, as the pipeline fills and its pressure increases, the CO2 enters a liquid phase. Subsequently, as pressure continues to increase, the CO2 returns to the gaseous phase and enters the supercritical state.
|
