Oil recovery enhanced

Enhanced oil recovery (EOR) requires the successful appHcation of chemical, chemical engineering, and petroleum engineering technologies (1). EOR accounted for about 3.2% of the wodd s 1994 oil production, ca 3 X ICf m /d (1.9 x 10 bbl/d) (2). In 1994, U.S. EOR production (113,000 m /d (709,000 bbl/d)) represented about 10% of total production. As the petroleum industry becomes more dependent on increasing production from existing fields, the use of EOR is expected to grow. 

The focus of more recent work has been the use of relatively low concentrations of additives in other oil recovery processes. Of particular interest is the use of surfactants (qv) as CO2 (4) and steam mobiUty control agents (foam). Combinations of older EOR processes such as surfactant-enhanced alkaline flooding and alkaline—surfactant—polymer flooding show promise of improved cost effectiveness. 

Oil reservoirs are layers of porous sandstone or carbonate rock, usually sedimentary. Impermeable rock layers, usually shales, and faults trap the oil in the reservoir. The oil exists in microscopic pores in rock. Various gases and water also occupy rock pores and are often in contact with the oil. These pores are intercoimected with a compHcated network of microscopic flow channels. The weight of ovedaying rock layers places these duids under pressure. When a well penetrates the rock formation, this pressure drives the duids into the wellbore. The dow channel size, wettabiUty of dow channel rock surfaces, oil viscosity, and other properties of the cmde oil determine the rate of this primary oil production. 

As reservoir pressure is reduced by oil production, additional recovery mechanisms may operate. One such mechanism is natural water drive. Water from an adjacent more highly pressured formation is forced into the oil-bearing formation by the pressure differential between the formations. Another mechanism is gas drive. Expansion of a gas cap above the oil as oil pressure declines can also drive additional oil to the wellbore. Produced gas may be reinjected to maintain gas cap pressure as is done on the Alaskan North Slope. Additional oil may also be produced by compaction of the reservoir rock as oil production reduces reservoir pressure. 

As the natural pressures in the reservoir decrease, oil production declines. The oil well may then be placed on-pump to maintain production at economic levels. The pump draws oil to the surface and lowers the height of the fluid column ia the wellbore. The pressure of a column of fluid can decrease the rate of fluid entry into the wellbore. 

Enhanced oil recovery (EOR) techniques seek to produce oil which would not be recovered using the primary or secondary recovery methods discussed so far. Three categories of enhanced oil recovery exist  

Chemical techniques change the physical properties of either the displacing fluid, or of the oil, and comprise of polymer flooding and surfactant flooding. 

Polymer flooding alms at reducing the amount of by-passed oil by increasing the viscosity of the displacing fluid, say water, and thereby improving the mobility ratio (M). 

This technique is suitable where the natural mobility ratio is greater than 1.0. Polymer chemicals such as polysaccharides are added to the injection water. - 

Miscible processes are aimed at recovering oil which would normally be left behind as residual oil, by using a displacing fluid which actually mixes with the oil. Because the miscible drive fluid is usually more mobile than oil, it tends to bypass the oil giving rise to a low macroscopic sweep efficiency. The method is therefore best suited to high dip reservoirs. Typical miscible drive fluids include hydrocarbon solvents, hydrocarbon gases, carbon dioxide and nitrogen. 

Secondary recovery techniques comprise injection of water in order to displace the oil and gas injection for maintaining the pressure of the reservoir. The cumulative yield of the primary and secondary oil recovery amounts to 38-43% according to Ref [24]. Success of this technique is mainly limited due to unfavorable wetting conditions. Especially in case of heavy oils, its high viscosity inhibits satisfactory yields merely using water for displacement. Due to the small viscosity ratio, the so-called fingering of the water at the water-oil interface is observed reducing the displacement effect. 

Seawater injection as a secondary mode produced 76.3% OOIP at 3.6 pore volumes. Afterward, aquifer water was injected as a tertiary mode and that increased 

Approximately 60% to 70% of the oil in place cannot be produced by conventional methods [22]. Enhanced oil-recovery methods gain importance in particular with respect to the limited worldwide resources of crude oil. The estimated worldwide production from enhanced oil-recovery projects and heavy-oil projects at the beginning of 1996 was approximately 2.2 million barrels per day (bpd). This is approximately 3.6% of the world s oil production. At the beginning of 1994, the production had been 1.9 million bpd [1254]. 

Enhanced oil-recovery processes include chemical and gas floods, steam, combustion, and electric heating. Gas floods, including immiscible and miscible processes, are usually defined by injected fluids (carbon dioxide, flue gas, nitrogen, or hydrocarbon). Steam projects involve cyclic steam (huff and puff) or steam drive. Combustion technologies can be subdivided into those that autoignite and those that require a heat source at injectors [521]. 

These are significant advantages of oil and gas wells over other geological formations. In addition, there is the possibility of enhanced oil recovery. 

The petroleum industry currently uses carbon dioxide for enhanced oil recovery (EOR). The gas may derive from a chemical plant, from an aquifer, or from a 

The second project is at Carson in California where the feed material for conversion to hydrogen will be petroleum coke (50001 per day) from a BP refinery. After reforming, the hydrogen will supply a 500 MW power station and the carbon dioxide (4Mt per year) will be pumped into an on-shore oil field. This plant should be on-stream early in the next decade. It has since been announced that General Electric is to link with BP with a view to building at least five such clean-coal electricity plants in the USA, with Carson being the first. 

The latest joint venture to be announced is a feasibility study for a large, clean-coal power plant in Western Australia. This also would generate 500 MW and capture up to 4 Mt CO2 annually for underground storage in an off-shore 

The above initiatives are illustrative of what may be expected in the near future where opportunities exist and the economics are right. Projects such as these are likely to be among the first major manifestations of hydrogen energy coupled to carbon dioxide sequestration. 

Fluorinated surfactants are effective in a variety of FOR techniques including (1) improving subterranean wetting, (2) increasing foam stability, and (3) modifying the surface properties of the reservoir formation by lowering surface tension and foaming properties to well-stimulation additives [69-72]. Both fluorotelomer [69] 

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Keywords compressibility, primary-, secondary- and enhanced oil-recovery, drive mechanisms (solution gas-, gas cap-, water-drive), secondary gas cap, first production date, build-up period, plateau period, production decline, water cut, Darcy s law, recovery factor, sweep efficiency, by-passing of oil, residual oil, relative permeability, production forecasts, offtake rate, coning, cusping, horizontal wells, reservoir simulation, material balance, rate dependent processes, pre-drilling. 

If the mobility ratio is greater than 1.0, then there will be a tendency for the water to move preferentially through the reservoir, and give rise to an unfavourable displacement front which is described as viscous fingering. If the mobility ratio is less than unity, then one would expect stable displacement, as shown in Figure 8.16. The mobility ratio may be influenced by altering the fluid viscosities, and this is further discussed in Section 8.8, when enhanced oil recovery is introduced. 

When considering secondary or enhanced oil recovery, it is important to establish where the remaining oil lies. Figure 8.21 shows an example of where the remaining oil may be, and the appropriate method of trying to recover it. The proportions are only an example, but such a diagram should be constructed for a specific case study to identify the target oil . 

Keywords production decline, economic decline, infill drilling, bypassed oil, attic/cellar oil, production potential, coiled tubing, formation damage, cross-flow, side-track, enhanced oil recovery (EOR), steam injection, in-situ combustion, water alternating gas (WAG), debottlenecking, produced water treatment, well intervention, intermittent production, satellite development, host facility, extended reach development, extended reach drilling. 

A considerable percentage (40% - 85%) of hydrocarbons are typically not recovered through primary drive mechanisms, or by common supplementary recovery methods such as water flood and gas injection. This is particularly true of oil fields. Part of the oil that remains after primary development is recoverable through enhanced oil recovery (EOR) methods and can potentially slow down the decline period. Unfortunately the cost per barrel of most EOR methods is considerably higher than the cost of conventional recovery techniques, so the application of EOR is generally much more sensitive to oil price. 

Proceedings of the 1992 International Conference on Microbial Enhanced Oil Recovery 40a Asphaltenes and Asphalts, I... 

An important application of foams arises in foam displacement, another means to aid enhanced oil recovery. The effectiveness of various foams in displacing oil from porous media has been studied by Shah and co-workers [237, 238]. The displacement efficiency depends on numerous physicochemical variables such as surfactant chain length and temperature with the surface properties of the foaming solution being an important determinant of performance. 

D. O. Shah and W. C. Hsieh, Microemulsions, Liquid Crystals and Enhanced Oil Recovery, in Theory, Practice, and Process Principles for Physical Separations, Engineering Foundation, New York, 1977. 

PEROXIDES AND PEROXIDE COMPOUNDS - ORGANIC PEROXIDES] (Vol 18) enhanced oil recovery [PETROLEUM - ENHANCED OIL RECOVERY] (Vol 18)... 

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