The April 19 issue of the Oil and Gas Journal featured their biennial survey and tabulations of enhanced oil recovery (EOR) projects all over the world, with special focus on the U.S. OGJ has surveyed EOR projects in the U.S. since the 1970s by compiling responses from questionnaires sent to the industry about their EOR projects. OGJ then tabulates pertinent data for each project. By 1980 OGJ had refined their tabulations and established a consistent pattern to present the data, a pattern that continues to this day.
The Long History of EOR
The attached graph summarizes OGJ’s EOR surveys for the U.S. since 1980, showing production from three broad categories of EOR processes and total EOR production. Total EOR production peaked at ~760,000 b/d during 1992-98, but then has drifted around 665,000 b/d since 2004. By studying the decades-long history of EOR in the U.S. we can estimate the likely trends for EOR going into the future.
In a series of eight Commentaries in 2007, I showed how each EOR process targeted oil fields with highly specific physical properties, fields that would best be labeled as non-conventional. OGJ’s 2010 EOR survey largely confirms this trend, with a slight shift by one category of EOR toward more conventional fields.
The graph represents results of EOR applications that followed three decades of research and field tests to determine which processes could extract additional oil beyond conventional pressure maintenance. Many U.S. oil fields were the world’s first to have most primary and secondary reserves extracted, and thus became proving grounds for EOR applications. So-called tertiary reserves would be targets of EOR processes.
The industry has long seen tertiary reserves as having a greater potential for recovery than primary and secondary reserves. Research during the 1950s and 1960s, however, revealed that EOR was not universally applicable to all fields. Instead, certain processes could be effective in oil fields with highly specific physical characteristics, typically outside the population of conventional fields.
Three Categories of EOR Matched with Field Properties
Thermal EOR (TEOR) – TEOR employs heat, usually injected steam, to extract oil. Throughout the 1950s steam was applied experimentally to a wide variety of depleted reservoirs to stimulate wells that produced mostly water. In most projects, however, incremental oil production was insignificant. After laboratory research and field tests, the industry concluded that steam injection was not economic for stimulating wells in most fields. However, steam was remarkably effective in non-conventional fields with highly porous and permeable reservoirs containing heavy, viscous oil. Steam delivered great quantities of heat that increased subsurface temperatures and reduced viscosities that mobilized the oil.
Steam injection scored huge successes in the vast heavy oil fields of Kern County, California. By 1969 TEOR topped 140,000 b/d and continued steep growth thereafter. TEOR peaked at 480,000 b/d in 1986 and continued to dominate the EOR world until 1990, thereafter tailing off to 292,000 b/d in the 2010 survey.
During 50 years of applications, TEOR has remained confined to heavy oil fields typical of Kern County. In the peak year 1986, Kern County supplied 87% of U.S. TEOR; the 2010 survey shows Kern County supplying 85%. The heat demand for steam generation is enormous. Since 1991, a 36-inch pipeline has transported ~1 billion cu ft of natural gas per day 900 miles from giant gas fields in southwestern Wyoming to the Kern County fields, dedicated to TEOR steam generation.
Gas Injection at Miscible Pressures – These processes involve injection of carbon dioxide, nitrogen, or natural gas into oil-bearing formations at sufficiently high pressures to create a mobile oil/gas phase that swells and fills subsurface pore space. With pressure applied from the surface, the oil/gas phase is pushed toward wellbores.
Miscible gas injection (MGI) was developed in the Permian Basin of West Texas during the 1950s and 1960s to extract oil that was locked in tight (low-permeability) formations that were typical throughout the region. By 1972 MGI was being applied to three giant fields in Texas, then to many other fields during the 1980s. Major MGI projects in low-permeability fields started up elsewhere: Jay field in Florida and Rangely field in western Colorado.
Since 2000, MGI projects have begun to show results in a few fields with moderately good permeabilities. In the 2010 survey, 12 such projects in Mississippi produce about 24,000 b/d of enhanced recovery, or 6.5% of total MGI production. Mature projects are regularly terminated, usually by operators who have concluded that MGI no longer achieves miscible pressures, and have reverted to conventional pressure maintenance. But 28 new projects since 2006 have raised MGI production, many of them outside the Permian Basin. In 2006 the Permian accounted for 54% of MGI; for 2010 the Permian contributes 48%.
Long-term, MGI appears to be the category that can be successfully applied more universally to depleted reservoirs. Because expansion beyond the Permian Basin has taken decades, widespread applications to high-permeability fields is likely to be slow.
Chemically Enhanced Waterfloods
The industry has attempted to flush additional oil from depleted reservoirs of high permeability by adding selected chemicals to waterfloods. However, this category of EOR has registered negligible amounts of incremental oil. Early fluid flow studies and pilot field projects showed that adding certain chemicals to injected water would enhance oil recovery over conventional waterfloods, so the industry targeted fields with moderate to good permeabilities. Chemical waterfloods, however, never reached 25,000 b/d, a mere blip on the EOR graph, and near zero since 1990. It appears, then, that the industry is limited to conventional waterflooding of high-permeability fields in the medium term.
EOR in the Future
The gradual emergence of MGI, the linkage between TEOR and heavy oil, and the failure of chemical waterfloods indicate that EOR will contribute important volumes to domestic supplies, but that applications to conventional oil fields will be strictly limited over the next decade or two. Nevertheless, the industry continues to speak of great potential for EOR. OGJ interviewed a leading engineer/scientist for a recent EOR symposium who spoke of “tremendous potential” for EOR in the U.S.: more than 218 billion bbl “lying unproduced in reservoirs shallower than 5,000 ft.” He also cited a study by Advanced Resources International: www.adv-res.com/pdf/v4ARI%20CCS-CO2-EOR%20whitepaper%20FINAL%204-2-10.pdf that says U.S. oil production could increase by 3 to 3.6 million b/d by 2030 if all captured CO2 were used for EOR.
I roll my eyes at such hypothetical projections that serve more to mislead than to inform. By any reasonable projection, the 50-year history of EOR shows that we should not expect MGI to be more than 600,000 b/d by 2030 (~250,000 b/d above present MGI). Total EOR would likely remain below 1 million b/d. At that rate the 218 billion bbl potential would take 600 years to be realized.
(Note: Commentaries do not necessarily represent ASPO-USA’s positions; they are personal statements and observations by informed commentators.)