Foam stimulation fluid

Batmgartner, S.A. and Mack, D.J. "On-Site Computer Monitoring of Foamed Stimulation Fluids," SPE paper 17531, 1988 SPE Rocky Mountain Regional Meeting, Casper, May 11-13. 

A foam, aqueous or non-aqueous, that is injected into a petroleum reservoir to improve the productivity of oil- or gas-producing wells. Some mechanisms of action for foam stimulation fluids include fracturing, acidizing to increase permeability, and diversion of flow. 

Foams are very compatible even with the most sensitive formations. The reduced liquid volumes, contact time, and fluid loss make foams one of the most versatile fluids for the stimulation of shallow, sensitive formations. References 6, 22, 25, 35, and 36 illustrate improved success of production by using foamed stimulation fluids. 

Foam stimulation fluids provide viable alternatives to stimulate low-pressure, fluid-sensitive gas wells where permeabilities are less than 5 md. Foams have been successfully used on shales, tight sandstones, and carbonates. Some interesting applications of foam fracturing have been on very sensitive formations and coal-bed methane fracturing. 

Presently, there are only a few constraints on foam. Economics limits the use of foams on deeper, high-pressure gas reservoirs because of the pressure limitations. Another limitation to foamed stimulation fluids, in... 

Perhaps the petroleum industry s most widely recognized advantage to using foam as a stimulation fluid is its ability to cleanup the liquid load fluid used to perform the fracture. Upon completion of the fracture treatment, the fracture fluid, after it has broken , should ideally be completely removed from the well. This step ensures that no residual polymers, fines, or unbroken gel will hinder the conductivity of the fracture. Also, a quick cleanup in order to bring the well back onto production is important. Fracture cleanup is accomplished by back-flowing the fluid from the formation to the surface. As the surface pressure is released, the gas within the foam expands, the foam stability is diminished, and the gas—liquid interface weakens. Further release of pressure at the surface will cause a... 

Foamed Fluids. N2 has been used in oil field stimulation work since 1961. In the mid 1970s, foamed fracturing fluid using N2 was developed. More recent uses of N2 foams in well stimulation involve well clean-outs and treatment diversions. 

A foamed fluid with a downhole quality of 75% may, for example, require a surface quality of 80%. (Foamed stimulation treatments are always stated in terms of downhole quality, surface quality is dependent upon zone, friction pressure, depth, and treating pressure.) A closed system is necessary to inject N2 because it is a gas. Therefore, the sand can only be added to the liquid portion of the foamed fluid. In this situation, the proppant, which is added to the liquid portion of the foamed fluid stream, must be added at 2000 kg/m3 in order to achieve a downhole concentration of 400 kg/m3. This condition illustrates that maximum downhole concentrations depend upon the downhole foam quality and the maximum proppant concentrations that the blender is capable of pumping. 

Foams are fluids that depend on shear history. The texture of a foam will reach an equilibrium state at a particular shear rate. Finer textured, more dynamically stable foams are produced at high shear rates, higher pressure, and with higher quantities of surfactant (36). Reidenbach et al. (11) observed that at higher shear rates, finer more uniform bubbles were created. This information indicates that at downhole conditions during fracture stimulation when conditions of high pressure and shear are present, foams are finely textured with parallel-piped uniform bubbles. 

Because of the nature of foams, the rheological character of foam fluids is difficult to quantify. The viscosity of foams is primarily dependent upon foam quality and external-phase fluid viscosity. Stimulation fluids are subjected to pressure variations from surface to downhole conditions therefore, foam quality and viscosity will change accordingly. In order to overcome the changing conditions experienced during stimulations, the foam fluids are designed to reach a specified quality at downhole conditions. 

Although foamed fluids are physically different than other types of stimulation fluids, their characteristics are important considerations in the design of fracture treatments. 

Fluid and Formation Compatibility. Foamed fluids are mixtures of gases and liquids. The volumetric ratio of gas is given by the foam quality for stimulation fluids. It is designed to be between 70 and 85%. The gas ratio remains high for several reasons and therefore, a reduced volume of liquid is available to contact the formation. For this reason, possibility of formation damage is reduced. 

Foams provide a viable alternative as a stimulation fluid in the well servicing industry. The application of foamed fluids must be suited to the particular characteristics of the reservoir in order to maximize the economic potential of the treatment. As long as foam treatments are implemented correctly in suitable reservoirs, the treatments will be successful and economic. 

Foam fracturing and stimulation fluids Foam acidizing fluid Gas well unloading foam... 

Foamed acids can be effective in improving contact with longer treatment intervals. As in fracture acidizing, most foams are 60-75 quality. The lightness of foam makes it an effective stimulation fluid for damaged gas wells. As with emulsions, the pumping of foam at high rates is not always possible. 

C. W., and B. D. Miller. 1974. New, low viscosity acid in oil emulsions. Paper SPE 5159, presented at the Society of Petroleum Engineers National Meeting and Exhibition, Houston. Ford, W. G. F. 1981. Foamed acid—an effective stimulation fluid. Journal of Petroleum Technology. July 7. 

Fluorinated surfactants are used in oil-well stimulation and for petroleum recovery by waterflooding [232] and in nonaqueous stimulation fluids for foaming hydrocarbon liquids (e.g., kerosine [233,234]). A foam, made by foaming a mixture of 1 % F(CF2)8CH2CH20(CH2CH20)2H in methanol, stimulates underground formations in the production of petroleum [235]. 

In most air and gas drilling operations, open-hole well completions are common. This type of completion is consistent with low pore pressure and the desire to avoid formation damage. It is often used for gas wells where nitrogen foam fracturing stimulation is necessary to provide production. In oil wells drilled with natural gas as the drilling fluid, the well is often an open hole completed with a screen set on a liner hanger to control sand influx to the well. 

King, G.E. Foam and Nitrified Fluid Treatments - Stimulation Techniques and More , SPE paper 14477, Distinguished Lecturer Program, 1985-86. 

Hydraulic fracturing and acidizing are the most common of the four stimulation methods. Foamed fluids are used in both hydraulic fracturing and acidizing, and thus will be the focus of this chapter. 

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