How Do I Use Bentonite-Free Polymer HDD Drilling Fluids?
Over the last few years, the popularity of pre-packaged, bentonite-free liquid polymer drilling fluid products has grown in the horizontal directional drilling industry.
These types of drilling fluid products offer many benefits and conveniences. The list includes not having to haul pallets of bentonite to the jobsite, dust-free mixing of drilling fluids, and not having to dispose of empty pallets and bentonite bags. Another big benefit is the ease of mixing, which is beneficial because new hires with little experience and training are often assigned to mix drilling fluids. Pre-packaged, bentonite-free products are less complicated to understand and use.
Along with benefits and conveniences of using such products, one must be very aware of the limitations. The chief limitation is that these products are designed for small-diameter and short-distance HDD projects only.
Most pre-packaged, bentonite-free liquid polymer drilling fluid products consist of four basic components, starting with a base product that serves as a replacement for bentonite. Then you have additives for sand and clay, and a clay drilling detergent or clay dispersant. These last three products, in varying amounts, adjust the base drilling fluid to the different soil conditions, similar to the way one would adjust a bentonite drilling fluid.
Just like a bentonite drilling fluid, soil identification is key to success. We do this by simply separating the soils into fine/reactive soils (reactive clays and silts) and coarse/non-reactive soils (sand, gravel and rock). If your doubt the soil type, take a clear container of water and go to the entry or exit pit. Grab some of the soil they are drilling through and stir it in. Fine/reactive soils may thicken the water and clay may stick to whatever one stirs with. Coarse soils will quickly settle to the bottom and the water will not thicken. This simple test gives HDD contractors direction as to where to go with the drilling fluid mix when referencing the drilling fluid manufacturer’s product user chart.
As previously mentioned, pre-packaged, bentonite-free liquid polymer drilling fluid products do have limitations. Utilized these products for only small-diameter, short (500-foot or less) HDD bores. Do not use them for exceptionally challenging, high-risk bores or soil conditions. Contractors uncertain whether their drilling fluid mix rises to the challenge can use a simple cup test, potentially saving a lot of headaches, money, downhole tooling and drill stem. Remember, the ability of a drilling fluid to suspend and transport drill cutting out of the borehole is one of its most important functions. Quickly test suspension using a clear container, such as a plastic water bottle with the top cut off. Pour in some of the drilling fluid mix, go to the entry or exit pit, and get a sample of the material they are drilling through. Aggressively mix the sample into the fluid, and set aside for a few minutes. If the solids settle to the bottom in the cup, they will settle to the bottom in the hole, resulting in frackouts, stuck drill stem, humped roadways, or stretched or stuck product line. Contractors can and should use this type of cup test for any drilling fluid to determine whether it will perform one of its most important functions.
Last, but not least, monitor drilling fluids returns. They are the closest thing to real-time data a contractor has for determining how the drilling fluid interacts with soils it encounters. Monitoring drilling fluids returns can indicate a change in soil conditions, which may require a change in the drilling fluids mix. Monitoring drilling fluids returns can also play an important role in preventing stuck pipe or costly damage to pavement or surface structures. When back-reaming on an HDD project, contractors should always have someone at the exit pit that monitors drilling fluid returns and can immediately notify the driller of signs of trouble. If the returns start coming back with the consistency of peanut butter, for example, the driller may need to slow down the back-ream speed slightly to get a more flowable consistency in the returns and prevent out-running the drilling fluid and over-pressuring the formation.
Pre-packaged, bentonite-free liquid polymer HDD drilling fluid products are convenient to use, cost-effective and can work well in the applications for which they were designed. For effective use, contractors need to understand the soil conditions, follow manufacturer recommendations, monitor return flow and know the limitations to these products.
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