Abstract
There have been several foam field applications in recent years. Foam treatments targeting gas mobility control in injectors as well as gas blocking in production wells have been performed without causing operational problems. The most widely used injection strategy of foam has been injecting alternating slugs of surfactant in brine with gas injection. This procedure seems to be beneficial as injection is easy to perform and control below fracturing pressure. Simultaneous injection of surfactant solution and gas may give difficulties, especially with interpretation of the tests, if fracturing pressure are exceeded during the injection period. This paper reviews critical aspects of foam for reservoir applications and intends to motivate for further field trials. Key parameters for qualification of foam are: foam generation, propagation in porous medium, foam strength and stability of foam. Stability is discussed, especially in the presence of oil at reservoir conditions. Data on each of these topics are included, as well as extracted summary of relevant literature. Experimental studies have shown that foam is generated at low surfactant concentration even below the CMC (critical micelle concentration). Results indicate that in situ foam generation in porous medium may depend on available nucleation sites. In situ generation of foam is complex and has been found to be especially difficult in oil wet carbonate rocks. Foam propagation in porous medium has been summarized, and propagation rate for a given experiment seems to be constant with time and distance. Laboratory studies confirm a propagation rate of 1–3 m/day. Field tests performed have not given reliable information of foam propagation rate, and future field pilots are encouraged to include observation wells in order to gain information of field-scale foam propagation. Foam strength is generally high with all gases. The exception is CO2 at high pressure where CO2 becomes supercritical. Stability of foam has been studied in laboratory and field tests, and has confirmed long-term stability of foam.
Highlights
Oil recovery by gas injections is the most widely used recovery method for light, condensate and volatile oil reservoir
This paper focuses on foam generation, propagation and stability in porous media in relation to enhanced oil recovery (EOR) processes
The foam generation ability was connected with surfactant concentration and was most profound for the alpha olefin sulfonate (AOS) surfactant, but the experiments showed that both surfactants generated foam even below critical micelle concentration (CMC)
Summary
Oil recovery by gas injections is the most widely used recovery method for light, condensate and volatile oil reservoir. Foam may increase the oil plateau period for mature oil fields by reducing the gas/oil ratio for wells suffering from high gas production The foam processes, both production- and injection well treatments, are considered rather low-cost processes. The efficiency of foam to reduce gas mobility (i.e., foam generation), the injection time required for foam to reach a given depth in the reservoir (i.e., foam propagation) and foam lifetime and persistence to various conditions during as well as after its placement (i.e., foam stability) are key questions for all intended field applications with foam in relation to EOR. The reservoir problems to be handled by foam treatment should be relevant to oil fields/reservoirs suffering from early gas breakthroughs, poor sweep efficiency of injected fluids, unwanted high gas production and/or undesirable high levels of gas recycling. The variables investigated were acid number, base number, oil viscosity, content of saturates and asphaltenes, interfacial tensions and spreading coefficients
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