Drilling fluid foam stability

Stable Foam. An oil and gas well drilling fluid foam that contains film-stabilizing additives, such as polymers or clays, and is pre-formed at the surface. See also Air Drilling Fluid, Foam Drilling Fluid, Stiff Foam. 

While drilling low-pressure reservoirs with nonconventional methods, it is conunon to use low-density dispersed systems, such as foam, to achieve underbalanced conditions. To choose an adequate foam formulation, not only the reservoir characteristics but also the foam properties need to be taken into account. Parameters such as stability of foam and interactions between rock-fluid and drilling fluid-formation fluid are among the properties to evaluate while designing the drilling fluid [13]. 

Neutralized sulfonated asphalt (i.e., salts of sulfonated asphalt and their blends with materials such as Gilsonite, blown asphalt, lignite, and mixtures of the latter compounds) are commonly used as additives in drilling fluids. These additives, however, cause some foaming in water or water-based fluids. Furthermore, these additives are only partially soluble in the fluids. Therefore, liquid additives have been developed to overcome some of the problems associated with the use of dry additives. On the other hand, with liquid compositions containing polyglycols, stability problems can arise. Stable compositions can be obtained by special methods of preparation [1407]. In particular first the viscosifier is mixed with water, then the polyglycol, and finally the sulfonated asphalt is added. 

Features Provides superior foam stability for stable foam drilling can be added batch-wise to the mist tank or metered into the mist fluid with a chemical pump Properties Cl. It. amber liq. dens. 8.62-8.82 vise. 6.5 cps flash pt. 131 F pH 11-12 100% act. 

Down-hole pressure fluctuations, due to the termination of flow in the annulus, are unquestionably of great concern. When circulation is stopped, during a connection or survey, for example, the foam can break-back to soapy water and its gas phase. The gas can then expand toward the surface. In order to re-establish circulation of foam, the "broken-back water in the bottom of the well must be displaced by newly introduced foam through the drill pipe. The BHP increases until the fluid begins to move up the wellbore. As the fluid is lifted out of the well, the BHP decreases, subjecting the formation to a dramatic pressure drop. In pressure sensitive formations this may have an unfavorable effect on borehole stability. In these cases, special additives can be used to create exceptionally stable foams. These foams are many times referred to as "stiff, or "stable, foams. 

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