Foam drilling stable

For stable foam drilling operations, much less volumetric rate of air flow is needed (i.e., usually less than 500 actual cfm). Also, the compressor should be capable of variable volumetric rate of flow and variable output pressure. The back pressure must be continuously adjusted to maintain a continuous column of stable foam in the annulus. This continuous adjustment of back pressure requires, therefore, continuous adjustment of input volumetric rate of airflow and output pressure (also, water and surfactant must be adjusted). 

Air and gas, unstable foam and stable foam techniques are used almost exclusively for onshore drilling operations, rarely in offshore applications. Aerated mud, however, is used for both onshore and offshore drilling operations. 

The downhole turbine motor designed to be activated by the flow of incompressible drilling mud cannot operate on air, gas, unstable foam or stable foam drilling fluids. These downhole turbine motors can only be operated on drilling mud or aerated mud. 

Foams can also be used to treat zones near bottom holes to remove solid impurities and for oil and gas well drilling. Stable foams are used in all of the above cases. In other cases, defoaming is necessary to provide a normal course of the processes. First of all, these are foaming in distillation and fractionation towers, producing oil well and well-head foams, fuel oil tank foams. 

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. 

Uses Foaming agent for mist and stable foam drilling under a wide variety of field conditions, particuiaiiy in high brines, hydrocarbon contamination and temps, in excess of 200 F... 

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. 

Chemical additives for gas-based drilling fluids are limited to surfactants (qv), certain polymers, and occasionally salts such as sodium or potassium chloride. An aqueous solution of the additives is iajected iato the air or gas flow to generate a mist or foam. No additives are used ia dry air or gas drilling operations. Gas-based fluids are not recirculated and materials are added continuously. As the fluid exits the well, air or water vapor escapes to the atmosphere, gas and oil are burned, and water and formation soflds are collected into a pit for later disposal. Stable foams must be destabili2ed to separate the air from the Hquid phase for disposal. 

In hard rock drilling areas with loss of circulation, the application of preformed (mixed at the surface) stable foam shows four to ten times higher penetration rate than clay-based muds. 

Stable Foam. When a well is drilled with stable foam as the drilling fluid, there is a back pressure valve at the blooey line. The back pressure valve allows for a continuous column of foam in the annulus while drilling operations are under way. Thus, while drilling, this foam column can have significant bottom-hole pressure. This bottomhole pressure can be sufficient to counter formation pore pressure and thus control potential production fluid flow into the well annulus. 

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. 

A drilling fluid comprising air, water, and a foaming agent (surfactant). These substances travel into a well as a mist, then change into a foam before returning up the annulus. See also Air Drilling Fluid, Stable Foam, Stiff Foam. 

In most practical systems, as the ones mentioned in the introductory part of this chapter, stable foams and emulsions are preferred. However, sometimes the development of a foam or emulsion is inconvenient, such as in oil drilling, in fermentation tanks, and in infusion preparations. It could also be that we prefer a foam or emulsion of intermediate stability, for instance, when compounds such as flavors in foodstuffs or drugs in medical products have to be released from the dispersed phase at a desired rate. 

The previous definitions aid in the understanding of the chemistry and engineering of foams and are critical when dealing with the formation and stability of foam structure. Persistent or stable foams consist of a network of thin liquid films, which exhibit complex hydrodynamics. For a drilling foam to remain persistent, or stable, several mechanisms are required to prevent the loss of liquid and gas from the foam and to prevent premature collapse of the foam, when subjected to environmental stresses. 

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. 

Resistance to Degradation by Oil Contamination Many wells, both vertical and horizontal, have been drilled using stable foam, with up to 40% by volume oil influx. Foam stability and BHP were maintained even despite this influx. 

Salt Contamination (Chlorides) Surfactants are available to effectively maintain stable foam in saturated aqueous solutions. An example application is using foamed saturated brine to drill through troublesome salt sections. 

Uses High foaming surfactant, hydrotrope for household and industrial hard surf, cleaners, shampoos, bubble bath, mild skin cleansers, down holefoamers, air drilling textile wetting agent Features Stable to acid and alkali... 

Uses Wetting and foaming agent for sat. brines incl. CaClj, HCI, NaCI, high-temp, acidizing drilling fluid additive removes oil-based muds prior to cementing or stimulation stable to 400 F stable to acids Properties Water-wh. liq. 50% act. 

Uses Detergent, wetting and foaming agent, emulsifier for liq. deteigents, shampoos, bath prods., wallboard mfg., textiles, drilling aux. exc. stability in hard water, alkalis moderately stable In acids Properties Pale straw pumpable paste m.w. 420-430 sp.gr. 1.05 vise. 40,000 cps pH 7-9 (1%) 68-72% act. 

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