In a perfect world, drilling fluids for each project would have exactly the right properties for the job at hand and the work would go as planned. But, sometimes, changing conditions downhole—e.g., shale, rock, sand or salt—require further modification in water loss properties, rheology control or viscosity modification. On site, particularly in small-footprint applications such as water well or horizontal directional drilling (HDD), there simply is not enough physical space to bring in complex equipment needed to disperse classical water soluble polymers. In these applications, a driller could be bringing a rig on to a homeowner’s front yard, between two buildings, or alongside a highway and not have the room for all equipment. In these “equipment challenged” applications or when faced with cold weather conditions, which also can slow mixing, polymers that easily disperse and become usable in a reasonable amount of time become necessary.
Drilling fluids are used to maintain wall stability, control fluid loss through their water-retention properties, enhance the ability to suspend cuttings and improve the ability to plug open formations. Whether water well drilling, HDD or tunneling, each project has its own drilling fluid requirements. The selection of additives is key in delivering value to the drilling operation and the friendliness of the drilling fluids.
Value consists of the many attributes that improve or facilitate the process, or create a financial return. It can be expressed, for example, in the form of:
• Process: higher productivity, less equipment needs, less waste;
• People: fewer needed, less training required, higher productivity;
• Equipment: lower capital, the expertise to run, safety, wear and tear;
• Materials: including warehousing and inventory management; and
• Time: process- and downtime.
Ashland Specialty Ingredients (ASI) has been a producer of acrylate and classical carboxymethyl cellulose (CMC) additives for decades—50 years in the case of the CMC products. ASI water-soluble polymers are used extensively as additives in numerous civil engineering applications to boost performance of bentonite-based drilling fluids through water retention, stabilization of the mud suspension and increased pumpability.
Recently, the company surveyed its customers to determine what they really needed from additives, particularly in the equipment-challenged situations. In a market dissatisfaction gap study, where 100 percent is a perfect storm of high importance and extreme dissatisfaction, the highest scoring attribute was increased dispersion properties of classical water soluble CMCs. Customers using drilling fluids modified in the field had problems with gels, lumps and non-uniform aggregates. To fill this dissatisfaction gap, ASI developed and launched a suite of dispersible CMC products—water-soluble polymers that are easy to disperse (ETD).
These ETD polymers, under the AquaVIS brand, are ideally suited for equipment-challenged jobsites. Faster dispersion enables the drilling fluids to quickly build viscosity, saving production time, material and effort. AquaVIS ETD polymers disperse uniformly, completely eliminating aggregates. Plus, they become water-soluble quickly, reducing mixing and cycle times. By contrast, classical CMC polymers either dissolve slowly or, in the case of fine materials, hydrate almost too quickly, going into solution nearly simultaneously. As a result, they gel and aggregate when stirred into solution.
The AquaVIS ETD polymers are tailored to partner with bentonite-based drilling fluids. These products are developed from classic CMC derivatives, and modified in a proprietary process to make them easy to disperse and to impart the resulting properties. Compatible with a wide range of drilling fluids and bentonites, they enhance viscosity and water retention properties of these materials.
ETD materials reduce mixing time because they fully disperse as they are added to bentonite-based drilling fluids. They don’t require specialized mixers, and they are used completely to modify viscosity or water loss properties when stirred in solution. As a result of the full utilization and the high viscosity of the additive, drillers can use less AquaVIS ETD water soluble polymer to achieve the desired water-loss retention and rheology modification properties.
The photographs illustrate the difference in dissolution between classical CMC polymers and an AquaVIS ETD polymer.
The photos on page 20 show pH-neutral aqueous solutions with, left to right, a coarse-grind CMC polymer, an AquaVIS ETD polymer and a fine-grind CMC polymer added. The coarse-grind polymer slowly went into solution and slowly built viscosity. After 10 minutes, the coarse CMC was still in particulate form.
While it would be expected that the fine-grade material on the right would hydrate quickly, it hydrated so quickly that it immediately formed lumps and large globular masses in solution. Ten minutes later, the aggregates were still present.
In the center, the ETD polymer dispersed into solution immediately and uniformly, with none of the problems exhibited by the classical CMC materials.
Out of the Laboratory and into the Field
Further application work has shown that AquaVIS ETD polymers are effective in aqueous solutions almost to freezing conditions. The ETD polymers were placed in water containing ice and the resultant temperature dropped to 46.4 degrees Fahrenheit (8 degrees Celsius). The AquaVIS ETD polymers dissolved easily into an ice water solution (see photo on page 22) and built viscosity very quickly. Knowing this, there would be no need to convert an ambient temperature or “cold” process into a warm one in cold weather conditions, saving time, cost and effort.
In the field, two water wells were drilled side by side to verify the efficacy of ETD polymers. One water-well used guar, a classical water soluble polymer, as the drilling fluid additive. The second used an AquaVIS ETD polymer. The chart on the right shows how the ETD polymer added value in several ways: reducing production hours, increasing preparation efficiency and reducing raw materials usage. Though the ETD polymer cost more, it reduced the overall cost through efficiency on drilling time and material utilization costs. Guar went into solution with gels, lumps and aggregates. Because these needed to be filtered, the utilization was 85 percent. Mixing time for the guar additive was approximately 38 hours more than the AquaVIS ETD polymers. At a North American labor rate of $30 per hour, the additional time cost $1,120. The well took roughly three weeks to drill, at $1,500 per day, for an equipment cost of $31,500 and a total project cost of $34,350.
AquaVIS ETD polymers are slightly higher priced than some classical polymers, so they added an extra 20 percent in raw material cost. But they yielded benefits that far offset the initial outlay. First, the utilization rate was 100 percent, as there was no waste. Due to the easy-to-disperse properties, there also was no additional mixing time for dissolution. As a result of the ETD polymer, drillers trimmed drilling time by several days, slashing equipment costs by more than $5,000. The total drilling costs were $6,300 less with the AquaVIS ETD polymer, for an 18 percent reduction in overall project costs. Now, not all sites will achieve these results. Some achieve a reduction higher than 18 percent, some lower. Work in the field has shown that there are many tangible benefits to consider that will lower costs and make jobs easier.
An added benefit that ETD polymers offer drillers in water well applications: AquaVIS ETD polymers are NSF ANSI 60-certified, so they can be used in potable water applications. This additional certification gives drillers peace of mind when managing potable water applications in civil engineering projects.
In sum, civil engineering drilling applications will benefit from all the known benefits and attributes of classical water-soluble CMC polymers, but will offer uniform, lump-free dispersions that facilitate faster drilling, put less wear and tear on the equipment and enable stable muds. Quick dissolutions in aqueous solutions save time and money, and enable drillers to reach high viscosities uniformly and predictably—benefits appreciated in equipment-challenged drilling applications.