I have the opportunity to discuss a wide variety of drilling scenarios and downhole issues around the world. I am always surprised when I ask, “Did you try drilling with foam?” and the driller says, “No, foam is too complicated.” Ironically, that statement has come from both mud drillers and air drillers. Foam drilling combines the best characteristics of both air and mud drilling. Drilling foam increases the ability to lift cuttings with air, while creating borehole stability similar to mud. As drilling formations change, the color of the foam will also change giving a key indicator of geological changes to the driller. Foam does not have to be complicated if you follow these four guidelines.
Not All Foaming Agents Are Created Equal
Foams allow a rig operator to lower the required air volume from the compressor to lift cuttings. The goal with foam is to drill deeper boreholes with a smaller compressor. However, there is a difference between using household or industrial soap and an NSF-certified Standard 60, designed for groundwater approved foaming agents. First off, NSF-approved drilling fluids are designed to prevent groundwater contamination; non-NSF approved soaps can contain phosphates, which are a known nutrient source for bacteria. Maybe you are thinking, “I am not drilling potable water wells and I do not need to worry about NSF-approved materials.” If that is the case, you need to reconsider and understand we are all responsible for protecting our groundwater. Yes, non-NSF-approved soaps can create bubbles, but not all bubbles are created equal. NSF-approved foams for drilling are engineered with a specific job in mind: to create a tiny, strong bubble capable of withstanding rigorous downhole conditions and carry drill solids from the bit to the surface.
Drilling foams are designed similar to firefighting attack foams, with the idea being that they can be used in harsh conditions and still expected to perform. The tiny, strong bubble structure is key to hole stabilization and hole cleaning. Like many drilling fluid additives, foams need to mix with water to activate. Recommended foam mixtures start as low as .5 percent by volume, and the recommended increase percent volume is 2 percent. Beyond manufacturer recommendations, I have had to use a 5 percent by volume foam in fractured loss-circulation zones. These foam mixtures are 95 to 99.5 percent water, and water quality is key to creating a healthy bubble structure capable of lifting half-inch sized cuttings. Foams work best at calcium hardness below 100 parts per million and a pH of 8.5 to 10. High chlorides in makeup water will inhibit foaming, and a salt-resistant foam will be required. I know that Baroid IDP manufactures salt-resistant foam. It is always best to follow the foaming agent manufacturer recommendations on water quality.
Proper Preparation and Mixing are Key
Once the water quality and quantity are correct, foams require proper preparation and time to mix. I have had great success by following the two-tank foam system. Each tank can be any desired volume, but to make it simple I always use 50-gallon or 100-gallon tanks. In a standard foam mix, the two tanks act as active system tanks. As one tank empties, the helper moves the suction hose to the second tank to continue with a 100 percent foam mixture that’s ready to pump. The two-tank system changes from two active tanks to a mix tank and an active tank when mixing polymers and bentonite gel foams. The mix tank will be used to mix and maintain the proper amount of polymer or bentonite slurry and once it has been sufficiently mixed, the foaming agent is added before switching the suction line. One tank can be used in a pinch for foam drilling but adding a secondary additive to a tank while injecting could pump un-yielded product into the injection pump, thus possibly plugging the pump.
Use the Right Foam for the Right Formation
Varying formations require a change in foam quantity or consistency. These formations can range from reactive clays, large gravel or fracture zones, to the most common variation, a water-bearing formation. The goal is to create foam with shaving cream-like consistency that stabilizes the borehole while carrying cuttings to the surface. Water-bearing formations will dilute the foam mixture. When the foam starts to thin out, the first step is to increase the injection rate until the shaving cream consistency returns. The next step is to increase the percent by volume mixture. Remember the basic mix is .5 percent and I have used up to a 5 percent mixture. A 5 percent mixture can lift large cuttings and overcome dilution of groundwater, but it is not cost-effective. A better solution is to augment the foam with polymers.
A stronger foam solution is a foam and polymer combination called “stiff foam.” These foams use either clay inhibitor polymers called PHPAs (partially hydrolyzed polyacrylamide) or a filtration control additive called PAC (poly anionic cellulose). Stiff foams utilize the polymer additive to create a stronger bubble that can lift more cuttings and stabilize the borehole. Stiff Foams also take on the polymers’ primary properties by either inhibiting clays or assisting in filtration control. Stiff foams require less air volume than a standard foam mix. The goal with stiff foam is to reduce air volume to drill fragile formations that straight air or foam would still damage. I have had great success drilling with stiff foam in clay and shale with Baroid IDP’s products, namely the AQF2 Foam mixed with QUIK-MUD D50. I have also had success in sands with AQF2 and either EZ MUD GOLD or QUIK-TROL GOLD. The goal is to stabilize a very porous zone. If the borehole cannot be maintained with stiff foam, a third solution is to change the foam consistency entirely by adding Wyoming sodium bentonite and foam.
“Gel foam” can create miracles. We are building a mud and foam combination that can be pumped with very low air volumes. Gel foams are excellent for loss circulation zones, fractures, cobbles and coarse gravel zones. The first step to gel foam is to mix a bentonite slurry just like we would for mud drilling. The mixture can be as light as 5 pounds of high-yield bentonite per 100 gallons of water or as much as 15 pounds per 100 gallons of water. The slurry should not be so viscous that it plugs or inhibits the performance of the injection pump. Once the bentonite is fully hydrated and no un-yielded material can be seen, the foaming agent is added and the gel foam is ready to pump. These foams can be further strengthened with PHPAs or PACs. I have had luck with several types of bits and gel foams, but never run gel foam through a hammer. The goal, like always, is to create a ½-inch size cutting that can be lifted out of the hole.
Know Why Foam Fails
The most significant reason foam fails is too much air. The goal is to create shaving-cream consistency foam that comes up out of the hole in one continuous column. If the foam coming out of the hole goes from column to air shooting up through it, we have a problem. Jeff Blinn, Baroid IDP training manager, calls this issue three-phase foam. Phase one is the foam moving uphole in a column, phase two is the air breaking the foam column, and phase three is the cuttings falling back downhole.
The next reason foam fails is lack of proper pretreatment of makeup water and mixing. If the water quality is excellent and mixing is adequate, it is time to check the manufacture date of the foam. Many foams have a shelf life. Injection pump limitation can also prevent a foam’s ability to overcome dilution to a new water source.
The final failure point of foam is a wrong application for the foam. Downhole water quality can affect the performance of the foam, along with a change in geology.
Stiff foams and gel foams will take more time to break down than standard .5 percent foam. You will need to create a containment plan for the foam on the surface. Consult with your foam manufacturer for the best way to break down foam with a defoamer or chemical combination to defoam. Many defoamers are not NSF-approved and can be toxic.
Foam is a tool that every driller should have in their toolbox. It allows for the use of lower-CFM compressors and the ability to drill fragile formations that high-CFM air or dense mud would damage. When I started as an intern with Baroid IDP, I laughed out loud when Blinn told me we could drill deep holes with bubbles. Carl Mason, IDP’s Dr. Mud Legend, was quoted saying, “Air is for breathing and mud is for drilling.” However Baroid IDP’s foam gurus like Blinn, Mark Whittle, and independent field consultant Mike West taught me how to utilize foams, stiff foams and gel foams. Drilling with foam combinations has helped me on projects around the world.