SIEVE TEST One simple test is to pour your fluid gently into a mesh sieve as shown in the picture on the previous page. After some initial flow-through, the fluid should come to rest, partially filling the sieve. When you shake the sieve, this fluid will flow through again like rain, leaving behind any suspended cuttings. Some of these cuttings can be as large as an inch across. Mixed-metal-type fluids are great for recycling systems. FILTRATE LOSS We have been taught that low filtrate loss is desirable in all drilling con-ditions — especially for sand, gravel and cobble geology. A mixed-metal system does not need good filtrate loss as tested by traditional API proce-dures. This is heresy to many of you, but real-world experience has proved this out. Anything you add to your mixed-metal system, no matter how low-charge it may be, can decrease the suspension of your system, and that suspension is the primary reason to use mixed-metal fluids. Very few things in this world are truly non-ionic. If we are lucky, we might be able to maintain 80 percent of our starting suspension ability after we add some “non-ionic” starch, but even these additives have some anionic char-acter that interferes with the magical associations between our mixed-metal additives and our clay. I have tested supposedly MMO-safe filtrate loss additives and, in some cases, found that my suspension had dropped to levels no better than running a standard bentonite mud. What a waste of money and potential. Now, that is not to say that there are no additives you can use to improve filtrate loss. Many mineral-based or plastic lost-circulation-materials can work. The swelling types of LCM and PROFITABLE . A 2.5-percent solids MMO fluid still sits on top of pea gravel in a graduated cylinder after 5 hours at room temperature. Note the pinkish rock that was picked up and suspended above the 800 mL mark. Source: CETCO Drilling Products DON’T LET LIMITED ACCESS LIMIT YOU Soil sampling in remote locations or in tight spots is no challenge for Little Beaver. The Big Beaver and the LST1G+, from our Lone Star line, deliver big power and easy portability to soil sampling jobs. See what Little Beaver’s drills can do for you. Lone Star Drills is a Division of Little Beaver, Inc. | www.LoneStarDrills.com LST1G+ BIG BEAVER wood fibers are not good choices (both are surprisingly anionic). PAC is best avoided. With that said, I also want to argue that filtrate loss is not all that import-ant for mixed-metal additive fluids. Loss with good mixed-metal fluids is surprising low. Firstly, we use these fluids at very low pump pressures with relatively low pumping rates. Secondly, these fluids will flow out into a forma-tion for only a few inches or so and then completely stop. This brings me to another good test to judge the quality of your mixed-met-al-additive fluid. Pour your mud into a glass-walled jar filled with a deep bed of pea gravel and put the jar somewhere quiet for a half-hour or so. A good MMO fluid will sit on top and not sink into the pea gravel beyond an inch or two. A poor-quality MMO fluid will eventual-ly flow to the bottom like a traditional drilling mud. Additions of CMC or PAC will not help your fluid stay atop the gravel, although those materials can cer-tainly slow it down. Only a good-quality mixed-metal fluid will completely stop just beyond the top of the rocks — and may even suspend a few. This introduction scratches the sur-face of the topic of mixed-metal fluids, including what they are and how to put them to work on your drilling jobs. Next month, we’ll take a closer look at methods for evaluating them, including using a shearometer and — my favorite — a ball harp. ND Greg Plutko is research and development scientist for CETCO Drilling Products, a Mineral Technologies Inc. com-pany. For more Drilling Fluids columns, visit www.nation-aldriller.com/drillingfluids. 800.227.7515 | Sales@LittleBeaver.com www.LittleBeaver.com /SoilSampling 26 NATIONAL DRILLER | FEBRUARY 2020 | NATIONALDRILLER.COM
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