Enhanced thermal recovery

Secondary recovery, infill drilling, various pumping techniques, and workover actions may still leave oil, sometimes the majority of the oil, in the reservoir. There are further applications of technology to extract the oil that can be utilized if the economics justifies them. These more elaborate procedures are called enhanced oil recovery. They fall into three general categories thermal recoveiy, chemical processes, and miscible methods. All involve injections of some substance into the reservoir. Thermal recovery methods inject steam or hot water m order to improve the mobility of the oil. They work best for heavy nils. In one version the production crew maintains steam or hot water injection continuously in order to displace the oil toward the production wells. In another version, called steam soak or huff and puff, the crew injects steam for a time into a production well and then lets it soak while the heat from the steam transfers to the resei voir. After a period of a week or more, the crew reopens the well and produces the heated oil. This sequence can be repeated as long as it is effective. 

Good thermal stability is a requirement for surfactants used in processes to enhance oil recovery. This applies most particularly to steam foam applications where surfactants such as AOS may be exposed to temperatures far above 100°C albeit for short times. Many authors have approached the problem of the thermal stability of a surfactant through a determination of the activation energy of the thermal degradation process. Once the activation energy is known, it can be used to estimate the rate of thermal degradation under various conditions. 

FIGURE 6.4 Steam flooding is one of two principal thermal methods for oil recovery and has been commercially applied since the early 1960s. A mixture of steam and hot water is continuously injected into the oil-bearing formation to displace mobilized oil to adjacent production wells. Reprinted with permission from Enhanced Oil Recovery. Copyright 1984 by the National Petroleum Council. 

The oil production from thin under-gas cap zones with an active aquifer is not efficient because of the rapid breakthrough of gas or water. The water-alternating gas technology based on the injection of water solution with oil-and water-soluble polymers seems to be promising to stimulate such wells. For heavy oils, this technology can be considered as an alternative to thermal-enhanced oil recovery [1673]. 

The cracking and the low-temperature oxidation of crude oils have been studied previously in order to simulate the thermal transformations of oil to gas and coke during enhanced oil recovery (1-6). Other authors characterize the thermal modifications of oil in the presence of a vapor phase (7)-... 

Thermally enhanced extraction is another experimental approach for DNAPL source removal. Commonly know as steam injection, this technique for the recovery of fluids from porous media is not new in that it has been used for enhanced oil recovery in the petroleum industry for decades, but its use in aquifer restoration goes back to the early 1980s. Steam injection heats the solid-phase porous media and causes displacement of the pore water below the water table. As a result of pore water displacement, DNAPL and aqueous-phase chlorinated solvent compounds are dissolved and volatilized. The heat front developed during steam injection is controlled by temperature gradients and heat capacity of the porous media. Pressure gradients and permeability play a less important role. 

Enhanced oil recovery (EOR) methods increase ultimate oil production beyond that achievable with primary and secondary methods. This is accomplished by increasing the proportion of the reservoir affected. EOR methods arc of three broad groups (1) thermal, (2) miscible, and (3) chemical. 

Schmidt, R.L. "Thermal Enhanced Oil Recovery Current Status and Future Needs, Chem. Eng. Progress, 47 (January 1990). 

Foams, in the form of froths, are intimately involved and critical to the success of many mineral-separation processes (Chapter 10). Foams may also be applied or encountered at all stages in the petroleum recovery and processing industry (oil-well drilling, reservoir injection, oil-well production and process-plant foams). A class of enhanced oil recovery process involves injecting a gas in the form of a foam. Suitable foams can be formulated for injection with air/nitrogen, natural gas, carbon dioxide, or steam [3,5]. In a thermal process, when a steam foam contacts residual crude oil, there is a tendency to condense and create W/O emulsions. Or, in a non-thermal process, the foam may emulsify the oil itself (now as an O/W emulsion) which is then drawn up into the foam structure the oil droplets eventually penetrate the lamella surfaces, destroying the foam [3], See Chapter 11. 

The general properties of supercritical fluids make them an attractive alternative to liquid solvents in column operations where transport effects come into play. If supercritical CO2 is employed as the solvent, this advantage is further supplemented by the non-flammable, non-toxic nature of the fluid, and the relative ease of solvent recovery. Supercritical solvents also offer the potential to greatly enhance thermally driven separations through dramatic changes in component solubility, adsorptive characteristics, and thermal conductivity near the critical region. 

Enhanced Oil Recovery The third phase of crude-oil production, in which chemical, miscible fluid, or thermal methods are applied to restore production from a depleted reservoir. Also known as tertiary oil recovery. See also Primary Oil Recovery, Secondary Oil Recovery. 

Overall thermal recovery can he enhanced by cogeneration and advanced technologies such as fluidised bed combustion with fuel pre-drying (6, 7). Useful heat conversion efficiency as a performance characteristic has been evaluated for small boilers using wood fuels, which adopted a combustion equation based on oxidation of lignin, cellulose and hemicelluloses including the effect of air, moisture content and the charcoal fraction in the ash (8). 

CO2 utilization possibilities identified and analyzed, address the potential of using the recuperated CO2 to enhance oil recovery, given that Romania would need a substantial quantity of 91 Mt of CO2 expected to be captured from flue gas from thermal power plants. 

Enhanced oil recovery is oil recovery by injection of gases or chemicals and/or thermal energy into the reservoir. It is not restricted to a particular phase, as defined previously, in the producing life of the reservoir. Another term, improved oil recovery (lOR), is also used in the petroleum industry. The terms EOR and lOR have been used loosely and interchangeably at times. Some feel that the two terms are synonymous others feel that lOR covers just about anything, including infill drilling and reservoir characterization. 

The thermally enhanced oil recovery process by steam flooding is a tertiary recovery method. A four-unit HTGR power plant with 200 MW(th) each for cogeneration of steam (530 °C, 15 MPa) and electricity (25 - 30 MW(e)) has been proposed to exploit the Duri oil field which currently represents the largest steam flood project in the world. Peak production has reached 300,000 bbl/d which requires 4,000 - 5,(KX) t/h of steam consuming 20 % of the oil produced. However, the present oil price development does not allow the economic employment of HTGRs for this type of oil recovery [57]. 

RAHMAN, A., et al.. Thermal Enhanced Oil Recovery in Indonesia, Prospect of HTGR Application, Non-Electric Applications of Nuclear Energy, (Advisory Group Meeting, Jakarta, Indonesia, 1995), IAEA-TECDOC-923, International Atomic Energy Agency, Vietma (1997) 91-102. 

Recommended well densities for use with thermal methods of enhanced oil recovery vary within a broad range from one well per fraction of one hectar to 10 or more wells per hectar. For example, for shallow reservoirs containing viscous crude oils, such as those of the Kenkiiak and Karazhanbas fields, the well densities of planned thermal treatment call for one well per 1 to 2.25 ha. At Usa oil field, of Upper Paleozoic age, with a thick 30-40 m petroliferous bed lying at depth of 1,400 m, a grid was used with a density of one well per 6.25 ha. For use with wet variants of in situ combustion, grids are possible with densities of one well per 10-16 ha. 

Emulsions formed in crude oil and bitumen during extraction operations are usually water-in-oil (W/O) macroemulsions (>0.1 to 100 om in diameter). Macroemulsions are kinetically stable, unlike microe-mulsions, which are thermodynamically stable. In conventional oil recovery (high-energy process), the crude is often in contact with formation water or injection water, as in secondary recovery. In tertiary or enhanced oil recovery, surfactants are used purposely in water floods to make microemulsions for enhancing the flowability of the crude. Crude-oil macroemulsions are produced when two immiscible liquid phases such as oil and water are mixed via the input of mechanical or thermal energy into the processes. Conventional crudes held under high pressures and temperatures amidst... 

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