EOR – Worldwide, over two million barrels of oil per day (bopd) are being produced from various EOR projects. In 1998, of 199 active U.S. EOR projects producing a total of 759,965 bopd, 66 projects were miscible CO2 floods accounting for over 179,000 bopd of production. U.S. EOR from steam injection accounted for 419,349 bopd of production, while hydrocarbon gas injection accounted for 102,053 bopd. Almost all U.S. steam floods are located in California, because of the state’s abundance of shallow, “heavy” oil, and almost all U.S. CO2 floods are in west Texas, because there’s a source of CO2 nearby to flood the deep, “light” oil reservoirs. (The above numbers do not include waterflooding, even though waterflooding an oil reservoir is common practice, many times as a pre-requisite to gas flooding, and accounts for significant enhanced oil production worldwide. Today, in California alone, active waterflood projects were injecting 2.2 million barrels of water per day adding about 140,000 bopd of production.)
EOR with CO2 – Basically, a miscible gas flood of an oil reservoir works because an injected gas becomes miscible, or becomes one liquid phase, with the oil, and helps the oil move through the rock reservoirs and up and out the wells. A gas (like CO2) is continually added to an oil reservoir by being compressed and pushed in, and when it is produced back out with the enhanced oil, it is recaptured and reinjected along with new gas, produced back out, added to new, re-injected, and so on, until as much enhanced oil has been produced as possible. MEI owns an interest in a mature CO2 flood of an oil reservoir in west Texas, started in 1983, which now adds 10 million cubic feet per day (cfpd) of new CO2 (piped in from New Mexico) to 30 million cfpd of CO2 being recycled from the enhanced oil production. That’s 40 million cubic feet of CO2, weighing 2,000 tons, handled and re-handled, every day.
Storage Capacity of Oil Reservoirs – A rule of thumb for miscible floods, considering the present base cost of CO2 and price of oil, is to (hopefully) produce each barrel of oil by adding only 5 to 10 thousand cubic feet of CO2 to the reservoir via the stream of cycling gas. After many years of production, when the returns of oil have diminished to the point of being uneconomic, the flood is shut in, and there would then be 5-10 thousand cubic feet of CO2 down in the reservoir for every enhanced barrel of oil produced during the life of the project. The 179,000 bopd produced under CO2 flood mentioned above are therefore storing 1 to 2 billion cubic feet of CO2 per day – that’s 75,000 tons a day. Too bad that’s not all captured waste CO2!
CO2 EOR Limitations – Economically successful EOR projects are difficult to predict because ultimately they are dependent on the vagueries of the geology miles below the earth’s surface, and the price of oil, both of which are difficult to predict with certainty. Traditionally, the farther away from abundant, naturally occurring CO2 in a relatively pure state, the less economic viability there was for a CO2 flood. The west Texas CO2 floods are near the CO2 deposits produced in New Mexico, and that’s why distant California has no active CO2 floods. But that’s changing as the energy industries wake up to the fact that their waste CO2 is a valuable resource for EOR.