Modified Seawater as EOR Fluid Could Boost Oil Recovery From Limestone Reservoirs Up to 60%
03 September 2008
 |
| Schematic model of the suggested mechanism for altering wettability using seawater. (A) Proposed mechanism when Ca2+ and SO42- are active. (B) Proposed mechanism when Mg2+ and SO42- are also active at higher temperatures. Click to enlarge. Credit: ACS |
Researchers at the University of Stavanger in Norway report that injecting a modified seawater fluid—“smart water”—into limestone oil reservoirs for enhanced oil recovery (EOR) could help boost oil extraction from those reservoirs by as much as 60%. Their findings are scheduled for the 10 September issue of the ACS journal Energy & Fuels.
In the study, Tor Austad and colleagues note that more than 50% of the world’s oil reserves are trapped in oil reservoirs composed of calcium carbonate, rocks that include chalk and limestone. The average oil recovery from carbonates is generally lower than for sandstone reservoirs. The reason, they note, is that the carbonate rock is neutral to preferentially oil-wet and often highly fractured.
The carboxylic material in crude oil adsorbs strongly onto the carbonate surface and makes it partly oil-wet. Injection of water is a cheap enhanced oil recovery (EOR) method, but in this case, the water will mainly follow the fractures. Because of the negative capillary pressure in oil-wet rock, water will not imbibe into the matrix blocks to displace the oil. The water will only displace the oil present in the fractures, and less than 5% recovery is therefore expected in some cases when the oil reservoir is highly undersaturated, e.g., Pres>>Pb and contains a large aquifer for pressure support.
—Strand et al. (2008)
Seawater is already being used as an enhanced oil recovery (EOR) fluid for hot, fractured chalk oil reservoirs because it is able to modify the wetting conditions and improve the displacement of oil. The symbiotic interaction between SO42-, Ca2+, and Mg2+, which are all components of seawater, removes some of the carboxylic material from the chalk surface, thereby increasing the capillary forces to promote spontaneous imbibition of water into the matrix blocks.
Studies on the use of seawater injection into chalk reservoirs have shown a 40%-60% increase in oil recovery. However, chalk is purely biogenic CaCO3, consisting of fragmentary parts of calcite skeletons produced by plankton algae, and is believed to have a more reactive surface than ordinary limestone.
The researchers collected core samples from Middle East oil reservoirs composed of limestone and soaked them in crude oil for several weeks. They then prepared batches of “smart water,”—seawater formulated with sulfate and other substances to improve seawater’s ability to penetrate limestone. In laboratory studies, they showed that irrigating the limestone samples with the “smart water” led to the same fundamental chemical reactions that occur in chalk.
In general, the type of interactions between SW [seawater] and limestone were similar to chalk, and the main conclusions drawn were as follows: (i) The chromatographic wettability test based on separation between the tracer, SCN-, and SO42- at the water-wet surface sites is also applicable to limestone; i.e., SO42- is adsorbed onto the surface. (ii) In a NaCl solution at room temperature, Ca2+ and Mg2+ appeared to have similar affinity toward the limestone surface. At higher temperatures, the affinity of Mg2+ was superior to that of Ca2+. (iii) In seawater, the relative interaction between Ca2+ and Mg2+ toward limestone is dictated by the presence of SO42-. Ca2+ appeared to adsorb more strongly than Mg2+ because of the ion-pair formation between Mg2+ and SO42- and the strong adsorption of SO42- onto the rock. (iv) The water wetness of a reservoir limestone core cleaned by toluene and methanol can be improved by flooding the core with seawater at high temperature, 130°C. Seawater can then act both as a cleaning agent and as a wettability modifier. (v) The oil recovery at 120°C by spontaneous imbibition was about 15% higher when the limestone core was imbibed with seawater compared to seawater without SO42- present, confirming that seawater will act as an EOR fluid/“smart water” also in limestone at certain conditions.
—Strand et al. (2008)
Upcoming experiments will verify if the efficiency in oil recovery is comparable to the observations in chalk, the scientists note.
Resources
Skule Strand, Tor Austad, Tina Puntervold, Eli J. Høgnesen, Martin Olsen, and Sven Michael F. Barstad (2008) “Smart Water” for Oil Recovery from Fractured Limestone: A Preliminary Study. ASAP Energy Fuels, doi: 10.1021/ef800062n
Large amounts of sea water are already being used. Perhaps large amounts of CO2 should be added to it. ..HG..
Posted by: Henry Gibson | 03 September 2008 at 11:52 AM
So they want to add (huge amounts of) CaSO4 to the water. How is CaSO4 made ?
Burn S : S + O2 --> SO3.
add H2O : SO3 + H2O --> H2SO4
add chalk : CaCO3 + H2SO4 --> H2CO3 + CaSO4 --> H2O + CO2 + CaSO4.
So, in addition of producing more polluting crude, they produce even more CO2 just for extracting it.
They could do part of the chemical reaction in the seawater that will be injected, in which case the CO2 will be sequestered too. Though, there is a big chance that will not be the case.
Posted by: Alain | 03 September 2008 at 12:29 PM
Better than blowing seawater down a hole might be this guy's idea of RF heating and them burning the H2:
http://www.scrippsnews.com/node/26728
Posted by: Sulleny | 03 September 2008 at 04:37 PM
@Alain,
CaSO4. 2H2O (gypsum) is a byproduct of phosphoric acid manufacture. I have to check, but I recall that each ton of phoshporic acid produces something like 4 tons of gypsum. Phosphoric acid being a key component in the manufacture of fertilizers, we have a lot of gypsum sitting around (currently being used for plaster, cement manufacture etc.).
The point here being that sulfur need not be burnt specially for making CaSO4, it is already being burnt to produce sulfuric acid (a raw material for phosphoric acid). (Phosphoric acid is made by the reaction of sulfuric acid with phosphate-containing rocks (apatites) yielding gypsum (a form of CaSO4) as a byproduct).
http://www.cheresources.com/wetphoszz.shtml
Posted by: Pradeep | 03 September 2008 at 06:06 PM
HG
The Water pumped into wells is used more as a flushing agent - it goes round and round so adding CO2 wouldn't help.
Statoil are already disposing +- 3000 tonnes/day CO2 underground offshore.
The formation they are using has an Area about 20000 square miles by 800 ft thick - they estimate 600 years capacity for current European Power station CO2 output.
It's expensive but Norway Govt would charge them 300 USD/tonne for CO2 pollution if they didn't.
Rob
Posted by: Rob Weir | 04 September 2008 at 05:27 AM
HG
The Water pumped into wells is used more as a flushing agent - it goes round and round so adding CO2 wouldn't help.
Statoil are already disposing +- 3000 tonnes/day CO2 underground offshore.
The formation they are using has an Area about 20000 square miles by 800 ft thick - they estimate 600 years capacity for current European Power station CO2 output.
It's expensive but Norway Govt would charge them 300 USD/tonne for CO2 pollution if they didn't.
Rob
Posted by: Rob Weir | 04 September 2008 at 05:28 AM
@Alain, Pradeep,
"They could do part of the chemical reaction in the seawater that will be injected..."
Adding the sulfuric acid to seawater will produce the gypsum within the reservoir, releasing CO2 to produce top pressure on the oil, and expanding the chalk/limestone creating higher pressure and fractures within the rock. This, in theory, could further enhance the oil recovery.
Posted by: Paul C | 04 September 2008 at 05:50 AM
This is signifigant as most of the oil in the middle east is held in carbonate rocks aka limestone. This doubles or triples the amount of recoverable oil from said carbonates. Given that average production from carbonates is 20% world wide going to 60% triples the recovery amounts or put another way Saudi's 260 billion barrels of URR can be upwards of 780 billion barrels at $106 a barrel thats $82,680,000,000,000 or 82.6 Trillion dollars. Some one is going to be very very rich with this technology.
OIIP – Oil Initially in Place = oil in the ground that is known to exist.
URR – Ultimate Recoverable Oil Reserves = what you can get out at with current market conditions and technologies
RF – Recovery Factor (URR/OIIP) = DUH
Posted by: | 05 September 2008 at 12:11 PM
anon:
You are of course assuming the current $$bbl metric and demand. I would assume that the electrification of transport alone will slash demand in half by 2025. Then there are the alternative biofuels. With the introduction of cellulosic E85 sans trade barriers and subsidies - the petro market erodes further and faster.
All in all the URR is a moving target - mostly downward. But the RF holds some promise provided other factors don't overwhelm it.
Posted by: gr | 05 September 2008 at 03:32 PM
biofuels are a pipe dream there is not enough aridable acres to replace liquid hydrocarbons, end of discussion the numbers are conclusive cellulose or not there just is not enought to replace 100+ QUADS of energy used in the USA every year. What ever the USA does not use the developing nations will. There is over 11 Trillion light conventional barrels in place world wide the world has recovered less than 20% of that total on average EOR is taking that number up to 60% or 3 times as much meaning that first trillion barrels that have been recovered is just 1 of 3 that can and will be recovered. or put another way it took 115 years to use the first trillion even keeping current usage rates trillions 2 and 3 will last at least 100 years there would still be 8 trillion left after the first 3 have been used. This takes not in to account heavy crudes 3 trillion more, tar sands 1.6 trillion, oil shale 1.66 trillion, coal 1.7 trillion tons in the USA alone, natural gas 5000 trillion cubic feet stranded world wide, unconventional gas in tight sands and shales in the USA 4000 trillion cubic feet and growing every year, methane hydrates on the order of 200000 to 4000000 trillion cubic feet the mallik hydrate production tests were a total success puting hydrate production costs at $4-6 MMBtu, no the world is awash in hydrocarbons and any price above $50 puts all the unconventional and hard to reach resources in reach, its a mineralogy axium that doubling the price of a resource opens 4 times the volumes to economic exploration this hold true for ANY mineral resource hydrocarbons included. I do this for a living so i would say i am an expert on hydrocarbons.
Posted by: Exploration Geologist | 09 September 2008 at 09:57 AM