When a drilling contractor has to work on equipment, they are well aware of the tools it takes to get the job done. For example, it would be impossible to tear into a mud pump and change pistons and liners with only a Phillips screwdriver or a 9⁄16-inch wrench. It takes a good collection of tools, each designed for a specific purpose, to complete the task. Without a complete set of the required tools, the job becomes much more difficult or, in some cases, impossible.
The same principles apply to drilling fluids. It is not uncommon to see drilling contractors dump high-yield bentonite into water, call it a drilling fluid, and expect it to perform all of the functions required, such as suspending and transporting cuttings, controlling fluid loss to maintain borehole stability, and/or controlling reactive clays. Just like the tools required for performing pump repairs, soda ash, bentonite drilling fluids products, polymers and additives are tools designed for specific purposes and if the right tools for the job are not used, the job becomes much more difficult or, in some cases, impossible.
One example is a water well drilling project that this writer/drilling fluid specialist visited in Mexico. The contractor was drilling a 16-inch diameter hole and was stuck at 1,500 feet deep, twisted off and had to fish the rest of the drill string out. The soil conditions consisted of sand and large gravel, and all they were running was bentonite and water (not Wyoming bentonite, by the way). Fluid loss was off the charts (which is why they could not keep the hole open) and gel strength was all but non-existent (could not suspend the sand and gravel). To make matters worse they did not have enough pump capacity to provide the adequate annular ascending velocity needed to carry the cuttings to the surface (even with a good drilling fluid).
Another example was a horizontal directional drilling project in Florida where the contractor was drilling in sand and using only high-yield bentonite and water (Florida water can be very hard). Upon arriving at location with one of my distributors, I immediately noticed how the drilling fluid would soak into the sand in the entry pit during the time it took to remove a drill stem as they were doing the back-ream/pullback, which they had just started. Ironically, the contractor talked about how he never used soda ash or polymers, and how he thought they were just a waste of money. As the pullback progressed, I watched how the rotary torque and pullback pressure climbed rapidly. I told my distributor that they were probably going to get stuck and it happened about halfway through the back ream/pullback process. The contractor had to dig up the reamer (fortunately, they were shallow enough) and split the project into two bores because he lacked the fluid loss control and gel strength to maintain borehole stability.
In both of the above mentioned drilling projects, failure to get the job done was costly yet easily avoidable, and failure was due to not using the right tools. Both contractors expected high-yield bentonite alone to perform a multitude of tasks and the end result was a loss of time and money. Many contractors mistakenly think that if they just run a thick drilling fluid it will solve the borehole stability problems caused by poor fluid loss control and help suspend cuttings, but I have seen drilling fluids with viscosities in excess of 165 seconds that had little in the way of gel strength or fluid loss control.
Photo 1 shows a bentonite drilling fluid mixed with untreated hard water. Note the clear water at the top when the drilling fluid is at rest. This indicates that the bentonite platelets are clumping together (flocculating) and falling out of suspension, and this drilling fluid is incapable of performing the functions needed to maintain borehole stability or suspend drill cuttings. In Photo 2, the example on the left is the filter press results (which indicate the degree of fluid loss) of the above mentioned sample. The example on the right is from a drilling fluid in which the water was pre-treated with soda ash and PAC (poly anionic cellulose) polymer was used to enhance the control of fluid loss. Note the difference in the amount of fluid released after running the test for 30 minutes at 100 psi. The higher the fluid loss results, the less capable the fluid will be at maintaining borehole stability. Also, in observing the two filter cakes one can see that the fluid mixed with untreated hard water yielded a thick yet highly permeable filter cake that just takes up much needed space in the borehole, while the sample on the right was thin yet sealed very well and would provide excellent borehole stability.
Pre-treating the mix water with the correct amount of soda ash (between and pound per 100 gallons of water) is essential and ensures that the bentonite is going to perform as it should. Identifying soil conditions and matching the drilling fluid and flow rates to the soil conditions is the next step. Problems encountered when drilling in coarse, non-reactive soils (sand gravel, rock) include fluid loss, borehole stability and suspension. PAC polymers enhance fluid loss control with a minimal effect on viscosity and gel strength enhancers can dramatically increase the gel strength/suspension without increasing the viscosity (higher viscosity fluids increase annular pressures) of a drilling fluid. Fine, reactive soils (such as clay) tend to stick and swell, causing bit balling and torque. Synthetic clay inhibiting polymers can address the problems of reactive clays and reduce torque and/or bit-balling.
The cost of using soda ash, polymers and additives pales in comparison to the problems resulting from not running a drilling fluid capable of performing the functions required in the various soils encountered. If contractors have questions regarding these products and how to use them, they should contact the manufacturer of the drilling fluids products they use for technical assistance. Soda ash, polymers and additives are tools that help match drilling fluids to soil conditions and, like tools in a toolbox, if used correctly, should save the contractor a lot of time and money along with saving a lot of wear and tear on drilling equipment.
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