Engineers propose new waterflood method for “significant” increase in oil recovery
04 September 2011
Engineers from the University of Houston and the University of Texas report that waterflooding with a surfactant—thereby altering the wettability of oil reservoir rocks—can increase oil recovery from 62 to 85%. In their paper in the ACS journal Energy & Fuels, they say the increase is “significant, and needs to be evaluated at the field scale.”
About 60% of the world’s remaining oil resides in carbonate rock reservoirs; the rock can be fractured or nonfractured, they note. Carbonate rocks tend to be “oil-wet”—i.e., in contact with an oil phase rather than a water or gas phase. Oil-wet rocks preferentially imbibe oil.
Current recovery techniques, such as waterflooding, recover only 40–50% of the original oil in place (OOIP) in nonfractured carbonates; the recovery is much smaller in fractured oil-wet carbonate reservoirs. Considering the large amount of oil in place, the poor waterflood recovery, and the increasing world energy demand, it is very important to improve oil recovery from carbonate reservoirs. In this work, we are interested in improving oil recovery from a low-permeability (2–5 md) nonfractured carbonate reservoir with a relatively low reservoir temperature (52 °C).
Enhanced oil recovery (EOR) techniques, such as CO2 flooding and alkaline/surfactant/polymer (ASP) flooding, have been developed to recover the remaining oil after waterflood. CO2 is miscible with oil at pressures higher than its minimum miscibility pressure and displaces oil miscibly. The sweep efficiency can be improved by water-alternating gas or foam injection. The key problem in applying CO2 flooding is the availability of a large quantity of CO2
Surfactants can be used to lower the interfacial tension (IFT) between oil and water and increase the capillary number to mobilize residual oil blobs. Polymers are used to improve the sweep efficiency by providing mobility control. Alkali can be used to generate in situ surfactants with acidic oils and increase pH to lower surfactant adsorption. ASP techniques were initially developed for sandstone reservoirs.
In the last 10 years, development of ASP techniques for carbonate reservoirs has received considerable attention. Even then, applications are limited to reservoirs with permeabilities of 20 md and higher because it is difficult to find polymers that can pass through lower permeability rocks and provide mobility control.
If EOR techniques cannot be applied, then the efficiency of the waterflood should be increased.
—Mohan et al.
Mohan et al. added a surfactant to a high-salinity injection brine. To make the process economically favorable, they focused on low surfactant concentrations, about 0.2 wt %. They chose a surfactant that changed the wettability to an intermediate wettability.
Using just brine (without surfactant), they found that secondary waterflooding recovers about 62% of the oil in about 3 PV (pore volume) injection and 80% in about 16 PV. Secondary flooding with surfactant recovered about 85% in about 3 PV and about 90% in 4 PV. Injection of 1 PV of surfactant solution followed by waterflood also recovers about 83% of the oil in a total injection of 3 PV.
In typical field waterfloods, 2–3 PV of water is injected. Thus, this increase in oil recovery from 62 to 85% is very significant. Future studies will be directed at optimizing the surfactant slug size.
—Mohan et al.
Resources
K. Mohan, R. Gupta, K. K. Mohanty (2011)Wettability Altering Secondary Oil Recovery in Carbonate Rocks. Energy & Fuels Article ASAP doi: 10.1021/ef200449y
Trying to get the very last drop of oil (to feed our gas guzzlers) by injecting a multitude of chemicals, salt, CO2 etc we may even manage to contaminate the fresh water table and eventually the useful top soil. Great news.
Posted by: HarveyD | 04 September 2011 at 08:14 AM
According to the study: "The key problem in applying CO2 flooding is the availability of a large quantity of CO2."
That statement gave me a good chuckle. While the rest of the world is trying to figure out how to get rid of CO2, down in Texas, they can't figure out where to find it.
Posted by: Allen | 04 September 2011 at 08:17 AM
There are enhanced oil recovery projects in development for west texas which will use CO2 to assist in producing more oil from old fields. One project I know of will consist of a brand new coal fired power plant using coal from the powder river basin brought into the Odessa-Midland area - CO2 produced from the plant will then be piped to oil fields in the area. The other project I know of that will be sending CO2 to texas is the mine-mouth Coal to Liquids plant in west virginia that will be sending it via pipeline. These are great ideas for American energy independence!
Posted by: ejj | 04 September 2011 at 10:37 AM
If all the plants had been built along the lines of the Wabash River Repowering Project, the air would be cleaner and we'd have a lot more oil coming out of Texas. But noooo, scrubbing sulfur is a green thing, we can't do that.....
Posted by: Engineer-Poet | 04 September 2011 at 11:57 AM
Canada buys CO2 and some SO2 for oil fields, from the US coal gasification operation in North Dakota. The SO2 helps in the process. Most of the remaining SO2 is made into fertilizer. Yes plants need sulphur, but not as acid rain.
Underground the SO2 is trapped by the minerals by ion exchange, and does not return to the surface.
In the future all coal should be converted to gas before being used in a power plant. Power plants that burn gas in engines can be as efficient but much less expensive than fuel cells. They can be operated in a way that make the capture of CO2 much easier.
Very low grades of coal at the mine can be consumed by wet-air-oxidation and the CO2 is almost automatically captured as a liquid in the high pressure process with not much additional effort. The fuel is so cheap that small multiple inexpensive, low efficiency steam turbines can be used for producing very low cost electricity with high reliability. ..HG..
Posted by: Henry Gibson | 06 September 2011 at 02:58 AM