Steam injection techniques

Three principal variants of steam treatment are (a) cyclical steam injection (steam soak or huff and puff ) (b) steam circulation technique and (c) area steam injection (steam flooding) (see Fig. 18). 

The respective advantages and shortcomings of each of the three variants are as follows  

For a period of 3-6 weeks, steam is being injected into the top and bottom of the reservoir through the tubing string of the producing well. Next, the well is shut-in for 2-3 days. It is then placed back in production. One and the same well is used both for steam injection and oil production. After the treatment, the well produces at a higher rate. The cycles of steam injection-oil production can be repeated several times. 

Advantages High oil yields follow the steam soak treatment heat losses along the well column are lower than with the other two techniques during the steam injection, the casing string is not heated as much as with the other two techniques. 

Steam is being introduced into the reservoir through the injection well and the oil displaced from the reservoir by the bank of hot steam condensate and steam is pumped up through adjacent production wells. 

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To date (ca 1997), steam methods have been appHed almost exclusively in relatively thick reservoirs containing viscous cmde oils. In the case of heavy oil fields and tar sand deposits, the cycHc steam injection technique has been employed with some success. The technique involves the injection of steam at greater than fracturing pressure, usually in the 10.3—11.0 MPa (1500—1600 psi) range, foUowed by a soak period, after which production is commenced (15). 

To ensure that the air is saturated when it passes through the water reservoir kept at the same temperature as the environment, the flow is maintained at the minimum level to provide adequate volume (e.g., 3 1/min is adequate for most detectors). Saturation efficiency needs to be considered when higher flows are used, however. By keeping the humidifier water at the same temperature as the environment, the relationship will hold. The air passing through the humidifier can only become saturated at the same temperature and thus, when it is mixed with the dry air, the percentage of RH is directly proportional to the ratio of wet and dry flows. This technique minimizes the need to manipulate flow adjustments to control RH if and when a heated water source is employed. It also eliminates condensation problems associated with heated water or steam injection techniques. 

The prevacuum technique, as its name implies, eliminates air by creating a vacuum. This procedure faciUtates steam penetration and permits more rapid steam penetration. Consequendy this results in shorter cycle times. Prevacuum cycles employ either a vacuum pump/steam (or air) ejector combination to reduce air residuals in the chamber or rely on the pulse-vacuum technique of alternating steam injection and evacuation until the air residuals have been removed. Pulse-vacuum techniques are generally more economical vacuum pumps or vacuum-pump—condenser combinations may be employed. The vacuum pumps used in these systems are water-seal or water-ring types, because of the problems created by mixing oil and steam. Prevacuum cycles are used for fabric loads and wrapped or unwrapped instmments (see Vacuum technology). 

Injection of Water or Steam at the Gas Turbine Compressor Exit. Steam injection or water injection has been often used to augment the power generated from the turbine as seen in Figure 2-42. Steam can be generated from the exhaust gases of the gas turbine. The HRSG for such a unit is very elementary as the pressures are low. This technique augments power and also increases the turbine efficiency. The amount of steam is limited to about... 

Combination of Evaporative Cooling and Steam Injection. The combination of the above techniques must also be investigated as none of these techniques is exclusive of the other techniques and can be easily used in conjunction with each other. Figure 2-44 is a schematic of combining the inlet evaporative cooling with injection of steam in both the compressor exit and the combustor. In this system, the power is augmented benefiting from... 

Techniques involving low-excess-air firing staged-combustion, and flue gas recirculation are effective in controlling both fuel NO, and thermal NO,. The techniques of reduced air preheat and reduced firing rates (from normal operation) and water or steam injection are effective only in controlling thermal NO,. These will therefore not be as effective for coal-fired units since about 80% of the NO, emitted from these units is fuel NO,. 

Conventional pump-and-treat techniques are not very effective in restoring aquifers impacted by DNAPLs. This ineffectiveness is a result of the relatively low solubility of the DNAPL and the large capillary forces that immobilize the nonaqueous phase. Over the past decade, several innovative and experimental strategies have been tested for more effective recovery of DNAPLs. These strategies include the more conventional use of surfactants, and thermally enhanced extraction or steam injection. Other more experimental approaches include cosolvent flooding and density manipulations. Each of these approaches is discussed below. 

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. 

The control of NO from stationary sources includes techniques of modification of the combustion stage (primary measures) and treatment of the effluent gases (secondary measures). The use oflow-temperature NO,.burners, over fire air (OFA), fiue gas recirculation, fuel reburning, staged combustion and water or steam injection are examples of primary measures they are preliminarily attempted, extensively applied and guarantee NO reduction levels of the order of 50% and more. However, they typically do not fit the most stringent emission standards so that secondary measures or flue gas treatment methods must also be applied. 

Since the Cold Lake crude used in this investigation has been exposed to the temperature of the pressuized steam used in the oil production, one cannot be certain that some thermal changes had not already occurred in the crude oil. To study this possibility the properties of cold bailed (i.e. recovered without steam injection) Cold Lake crude asphaltenes are being investigated by many of these same techniques and will be described in a future report. 

Dilution steam Injection. First stage (light feed) or second stage (heavy feed). By using this technique, coke formation from heavy oil in convection section coils can be minimized. 

Fig. 18. Three techniques of steam injection into the reservoir and bottomhole zone a -steam soak b-steam circulation c-steam flooding...

An examination of the kinetics shows that if the lower limit of practical retention time is reached, it is advantageous to lower the acidity and raise the temperature. It is also evident the pretreatrhents which accelerate the rate of hydrolysis and increase the heat of activation are advantageous. Microtechniques are now available which can establish yields on milligram samples heated in glass capillaries with reaction times of a few seconds and internal pressure in excess of a 1000 Ibs/sq in but they have not yet been applied to this problem. Pumped hydrocellulose slurries can be heated by steam injection and quenched by release of pressure, but the practicability of such a processing technique has not been established. 

The oil recoveries obtained from steam stimulation processes are much smaller than the oil recoveries that could be obtained finm a steam drive. However, it should be apparent that the steam stimulation process is much less expensive to operate. The cyclic steam stimulation process is the most common thermal recovery technique. Recoveries of additional oil have ranged firom 0.21 to 5.0 bbl of oil per barrel of steam injected. 

Large heat losses continue to be associated with thermal processes. The wet combustion process has lowered these losses for the higher-temperature combustion techniques, but the losses are severe enough in mat r applications to prohibitthe combustion process. The losses are notas large with the steam processes because they involve smaller temperatures. The development of a feasible downhole generator will significantly reduce the losses associated with steam injection processes. 

Up to this point only the steam distillation of sparingly miscible solvents such as hydrocarbons or chlorinated hydrocarbons has been considered. The evaporation, using direct steam injection, of fiiUy water-miscible solvents with atmospheric boiling points below 100 °C is different in principle and is commonly practised. Whereas in the case of immiscible solvents, dry distillation was shown to require less heat and therefore would be more attractive, unless a difficult residue made it hard to carry out, there is no such advantage in this case. Any used solvent of this sort, whether or not it contains a difficult residue, can be evaporated by injecting steam into it, thus avoiding the need to have a reboiler or evaporator. This can be a useful technique if the solvent contains, for instance, halide salts that would require a heat exchanger made of exotic metals. 

The feasibility of using adsorbents, particularly activated carbon, as an alternative to steam stripping or chemicals injection techniques, for the removal of volatile organic compounds from an SBR latex is demonstrated using batch... 

In the first attempt over 100 years ago, to blow-mold hollow objects, two sheets of cellulose nitrate were clamped between two female mold halves. Steam injected between the sheets softened the material, sealed the edges, and expanded the heated sheets to form the inside shape of the two female mold halves. The high flammability of cellulose nitrate, however, limited the usefulness of this technique. 

The method of distillation employed depends on the nature of the feed material. Over the years all the prime aromatic materials have been investigated to establish optimum conditions. Generally water distillation gives the finest quality oil as in this technique there is less chance of damage to sensitive components. Steam distillation may impart a burnt character, which can result from internal condensation and flowback of an aqueous extract onto the exposed steam injection coils. 

Steam injection — This is the older method and is carried out in jacketed stills fitted with a suitable separator to permit either continuous recycling of the distillate where water is used in the still or its rejection where high-pressure live steam is injected. Contact of oils with boiling water and/or steam can lead to decomposition of certain constituents so that conditions must be very carefully controlled. Dry distillation in vacuo is now the more widely used technique. 

Various types of equipment and techniques have been employed to suppress foam formation in biological and process equipment. These include both chemical and mechanical methods. Chemical methods include various defoaming chemicals (silicone oils, non-ionic surfactants, etc.) Mechanical methods employ sprays, wire mesh elements, heat, live steam injection, air or steam-operated ejectors, sonic horns, vacuums, centrifuges, and the use of large re-... 

Steam is injected into a reservoir to reduce oil viscosity and make it flow more easily. This technique is used in reservoirs containing high viscosity crudes where conventional methods only yield very low recoveries. Steam can be injected in a cyclic process in which the same well is used for injection and production, and the steam is allowed to soak prior to back production (sometimes known as Huff and Puff). Alternatively steam is injected to create a steam flood, sweeping oil from injectors to producers much as in a conventional waterflood. In such cases it is still found beneficial to increase the residence (or relaxation) time of the steam to heat treat a greater volume of reservoir. 

Domestic petroleum, natural gas, and natural gas Hquids production has declined at a rate commensurate with the decrease in reserves (see Table 2). Consequently, the reserves/production ratio, expressed in years, remained relatively constant from about 1970 through 1992, at 9—11 years (16). Much of the production in the early 1990s is the result of enhanced oil recovery techniques water flooding, steam flooding, CO2 injection, and natural gas reinjection. 

Steam can also be injected into one or more weUs, with production coming from other weUs (steam drive). This technique is effective in heavy oil formations but has found Httle success during appHcation to tar sand deposits because of the difficulty in connecting injection and production weUs. However, once the flow path has been heated, the steam pressure is cycled, alternately moving steam up into the oil zone, then allowing oil to drain down into the heated flow channel to be swept to the production weUs. 

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