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5.2 Permian Basin and Worldwide CO2 Flooding History
In the USA, CO2 EOR technologies have been demonstrated to be profitable in commercial-scale applications for more than 30 years. Large-scale CO2 EOR was first demonstrated in the Permian Basin of West Texas with the SACROC and North Cross floods in the early 1970s. Since then, CO2 EOR has been deployed selectively throughout the world, but very extensively in the Permian Basin since the mid-1980s. Historic CO2 EOR projects have largely injected high purity, low cost CO2 obtained from natural CO2 reservoirs, but an increasing percentage of natural gas byproduct CO2 is also being injected. An extensive CO2 pipeline network has been developed in the Permian Basin region to meet the growing CO2 requirements of the CO2 EOR sub-industry.
The most comprehensive public review of the status of EOR projects around the world is the biennial EOR survey published by the Oil and Gas Journal; the most recent issue of which was published in April 2010.5 According to this survey, 105 CO2 EOR projects currently provide nearly 250,000 barrels per day of incremental oil production from EOR in the USA. Of these, the vast majority, 100 projects producing 240,000 barrels per day, are miscible6 CO2 EOR projects.
It is well known that water and oil do not mix together. The technical term used for this is immiscible. However, other gaseous and liquid substances have the property of mixing with oil and are thereby ”miscible.” This miscibility property is dependent not only on the nature of the two substances but the pressure and temperature at which they come in contact. CO2 and many oils are miscible at common reservoir pressures.
When CO2 is injected into a well and moves out into the water-flooded region, it will contact oil that was bypassed by the water. The oil that is contacted becomes a mixed substance and takes on new properties independent from either the single phase CO2 or the oil. The mixed substance can mobilize the oil by making it lighter and free to move off the rock surfaces to the producing wells. The moving oil/CO2 continues to contact oil, freeing more oil as it progresses, with the mobilized oil all being driven along from the injector wells to the producing wells.
Twelve years ago, production from CO2 EOR was only 170,000 barrels per day from 60 projects. Since 1986, over 1.3 billion barrels of incremental oil has been estimated to have been recovered using this technology.
Figure 5.2.1 provides the location of the currently active USA CO2EOR projects (inclusive of the Weyburn and Midale projects in Canada), and including the large serving pipelines together with the sources of CO2 supply.
Figure 5.2.2 tracks the steady growth in CO2 EOR production in the USA and Permian Basin for the past 25 years, noting that the Permian Basin dominated worldwide projects through 2005 and started to become less dominate as new EOR interest ramped up in the Gulf Coast and the Rockies. Notably, this CO2 EOR growth was sustained in spite of two oil price crashes, the first in 1986 and the second in 1998. With only a few exceptions, CO2 EOR projects continued to operate through the periods of low prices, and increased their CO2 purchases after resumption of “normal” oil pricing. It is significant to note that low oil prices did not deter underlying growth in the CO2 EOR industry, but only curtailed acceleration of the growth.
Figure 5.2.1 – USA CO2 Sources and EOR Regions
Figure 5.2.2 – Growth of CO2 EOR Projects
A look at the CO2 EOR production (Figure 5.2.3) illustrates that the great majority of CO2 EOR production has been in and is still being produced from the Permian Basin. The observable Permian Basin decline in recent years is a very interesting occurrence that Melzer Consulting believes is due to a combination of:
- the lack of sufficient supply of CO2 to sustain increasing project growth; and
- maturation of existing projects which are less efficient on a per million cubic feet (mcf) basis but yet quite economical in today’s oil price environment.
Figure 5.2.3 – Worldwide and Permian Basin CO2 EOR Production
As previously mentioned, the birth of the worldwide CO2 EOR industry occurred in the Permian Basin with two large-scale projects in the early 1970s. A group of oil companies led by Shell and Gulf effectively converted a waste stream of by-product CO2 from natural gas processing facilities in the southern portion of the Permian Basin into a useful commodity by capturing, compressing and routing it via the first CO2 pipeline to the North Cross unit near McCamey, Texas, and then on to Snyder, Texas and the SACROC unit in Scurry County. The response of the reservoirs to the CO2, especially in the carefully observed four-pattern area of SACROC, convinced several other major oil companies of the viability of CO2 injection.
Based on these results, plans were conceived to bring several large underground sources of natural CO2 to the region. These very pure (>95%) supplies of CO2 came from Bravo Dome in northeastern New Mexico, Sheep Mountain in south central Colorado, and McElmo Dome in southwestern Colorado. Locations of these supplies are shown in Figures 5.2.1 and 5.2.4.
Figure 5.2.4 – Location of Oil Fields and CO2 Supply Pipelines in the Permian Basin
With these new supplies, the next phase of activity witnessed several key fields deployed into CO2 EOR operations. Most notable of these were the Wasson, Seminole and Slaughter fields, all Permian-age San Andres formation fields; each with 1-3 billion of barrels of original oil in place. It is also notable to observe that CO2 flooding is continuing on these projects today, some 25-plus years after original implementation.