The Evolving Challenges of Well Development

Published On: March 19, 2024By Categories: Drilling, Features, Groundwater Quality

Today’s bentonite requires revisiting development practices.

By Michael Schnieders, PG, PH-GW, and Edd Schofield

Well development continues to be a topic of discussion in our industry, and for good reason.

Well development is a crucial process conducted after the initial drilling of a water well. Development involves specific techniques and methods to improve the well’s efficiency, maximize water yield, and enhance water quality. It has been said—and laboratory data of existing wells continues to confirm—that improper or inefficient development will haunt a well over its entire operational lifetime.

Two main challenges of effective well development include understanding the importance of the process amongst our clients and ourselves, and understanding what various processes are most effective. In previous articles in Water Well Journal, our colleagues have discussed the importance of well development. In this article, though, we will discuss the challenges in drilling fluids that are impacting the process.

Drilling muds, now more commonly referred to as drilling fluids, are specially designed mixtures used in the drilling process, including water wells, oil and gas wells, geothermal wells, and environmental wells.

These fluid mixtures serve multiple functions throughout the drilling process. The primary purposes of drilling fluids include cooling and lubrication, cuttings removal, borehole stability, and pressure control. In some cases, they can assist in limiting corrosion of equipment, reduce fluid migration, and aid in formation evaluation.

In the groundwater industry, there are two main types of drilling muds: water-based bentonites and synthetic-based muds. These categories are defined by the base fluid, but over time with the advancement of additives, the two have become even more similar.

The selection of the appropriate drilling fluid depends on factors such as the geological formations being drilled, the type of well, and the specific drilling objectives. The composition of drilling muds includes a combination of base fluids, additives, and chemicals tailored to meet the requirements of the specific drilling operation. In the groundwater industry, bentonite is the most common component of drilling fluids.

The History of Bentonite

Figure 1. Drilling fluids remain in a recently completed active well system, post-traditional development, impacting the production zone, well efficiency, and water quality.

Bentonite is a type of clay that is composed primarily of smectite minerals, such as montmorillonite. It is derived from volcanic ash deposits that have undergone weathering over time. Bentonite has the unusual property of expanding several times its original volume when placed in or encountering water. This property helps in the drilling process as it gives the fluid a viscosity several times that of water.

There are several significant bentonite deposits that are commercially viable for well drilling and other industrial applications in North America. Some of the prominent locations with substantial bentonite reserves include Wyoming, Montana, and California in the United States, and Alberta and Saskatchewan in Canada.

These regions have been historically important sources of bentonite for well drilling due to the quality and quantity of deposits. The bentonite extracted from these areas is often used in the formulation of drilling fluids for water well drilling.

The specific properties of bentonite from different deposits can vary, and industries may choose sources based on the desired characteristics for their applications. The deposits in Wyoming, in particular, are known for some of the largest and highest-quality bentonite deposits in the world. The Green River Formation, located in the Big Horn and Powder River Basins, as well as other parts of Wyoming, contain extensive
bentonite beds.

The sodium-rich bentonite from Wyoming is typically preferred for drilling applications due to its high swelling capacity, low permeability, and excellent rheological properties. From a visual, physical sense, the bentonite deposits can vary in color, which reflects the core mineralogy and presence of impurities, all of which can impact the swelling characteristics and usability.

Two main challenges of effective well development include understanding the importance of the process amongst our clients and ourselves, and understanding what various processes are most effective.

The Need for Polymers

The high-quality bentonite deposits found in North America have been extensively utilized in various industrial applications for decades.

Unfortunately, this increased demand has also led to a gradual depletion of the purest reserves, making lower-grade bentonite material more prevalent in the market. While lower-grade bentonite may still offer a number of benefits during drilling, we are seeing an increased need for polymer additives during the drilling process to compensate for the current requirements of using lower-grade clay deposits.

Figure 2. Cloudy behavior typical of uniform clay particulate and added polymer presence, enhancing sediment entrainment and challenging development (200x magnification).

Polymers are introduced into drilling fluids to enhance their rheological properties, viscosity control, and lubricity. These polymers work synergistically with these lower-grade bentonites, compensating for its limitations and ensuring the proper suspension of cuttings, efficient hole cleaning, and enhanced wellbore stability.

The use of polymers not only addresses the challenges associated with the diminishing quality of bentonite but also contributes to the current challenges of proper well development. Prior to 2000, polymer inclusion in bentonites was limited to a handful of manufacturers with less than 1.5% (by weight) additive observed.

Fast forward to 2020 and the percentages have increased dramatically to levels between 10% and 15% (by weight) with little advertisement or notice of their addition to the drilling industry. This increased use of polymers in drilling fluids has become a prevalent trend, driven in part by the need to compensate for the use of lesser-grade bentonite in drilling operations, as well as an effort to enhance the overall drilling
process.

As was stated, polymers contribute to the improvement of drilling fluid properties by providing enhanced viscosity control, increased lubricity, and improved rheological characteristics. These polymers, which have historically included xanthan gum but are now primarily synthetic derivatives, serve to benefit these lower-grade bentonites in all the aforementioned requirements of drilling fluid.

The Challenges in Development

In evaluating reported failed well development efforts in the field from across the country, our lab has reportedly seen two distinct indicators. First, phosphorus levels are high as identified in phosphate and phosphorus tests. Second, microscopic identification of polymeric absorption and glass transition behavior is evident.

Phosphate polymers are often specifically employed to enhance poor-grade bentonite due to their versatile properties that complement and compensate for the limitations of the lower-quality clay. The addition of phosphate polymers helps mitigate these shortcomings by improving the fluid’s ability to form a stable filter cake on borehole walls, minimizing fluid loss into surrounding formations.

Phosphate polymers also contribute to inhibiting shale swelling, enhancing lubricity, and maintaining overall borehole stability. The compatibility of phosphate polymers with common water chemistry conditions is also beneficial, ensuring consistent performance in various water qualities as well as an ease of regulatory approval (National Sanitation Foundation) and water industry acceptance due to widespread use in water treatment efforts.

Polymers will continue to be widely used in the water industry for a variety of reasons. Understanding their limitations and compatibilities is often site specific—whether we are discussing well development or water treatment like jar tests results seen in the lead photo.

Figure 3. Enhanced drilling mud in which the polymer level is super saturated and has reached the glass-transition phase, resulting in a hardened fouling mechanism that is more challenging to develop using traditional. development practices (100x magnification)

In evaluating well development challenges, a signature that we have identified is an increase in phosphorus levels. This ordinally was observed in tracking total phosphate and polyphosphate levels and has expanded into total, reactive, and acid hydrolyzable phosphorus testing.

In wells with visual and operational confirmation of poor development (Figure 1), total phosphorus levels have ranged from 73.4 mg/L to as high as 440 mg/L, far in excess of typical background levels. When present at a saturated level such as these, degradation is slow, concentrations evident in wells seven to 15 years after completion.

The lingering effect of these polymers is also evident in microscopic evaluation of water samples of impacted wells. The physical evidence presents itself either in a cloudy or turbid behavior (Figure 2) or in sheer type of behavior called the glass-transition (Figure 3).

With the polymer enhancements evident, we as an industry are challenged with how to best respond to these changes. As a practice, well development should incorporate both physical (mechanical) methods as well as chemical methods.

Once traditional mechanical development has been utilized to largely address buildup within the column, a highly oxidative (chlorine treatment) is necessary to break down the polymers for subsequent removal. In this form of treatment, we recommend an elevated sodium hypochlorite treatment to oxidize and destabilize the polymers, allowing for removal.

Vastly different than disinfection concentrations, in this use of chlorine, you will require a minimum of 1000 ppm of chlorine present. While this level of chlorine can be corrosive to steel, the contact time is limited to swabbing the solution into the perforated zones evenly, which upon completion, evacuation can begin.

Once completed, use of a phosphate-free mud dispersant such as Nu-Well 220 (see video in sidebar) can be effectively used to reduce swell and collapse the clay molecule, enhancing physical development. Mechanical development and over-pumping are then advised to evacuate the material and complete the effort.

Monitoring during development to include visual turbidity, pH, and conductivity are strongly encouraged to ensure removal of the material. These parameters can be evaluated on site, with more laboratory-based testing (phosphate, phosphorus) conducted off-site, once complete. Confirming removal with visual inspection (video survey) and operational data (pump test) are also recommended.

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The additional levels of polymers in conjunction with bentonite has helped to compensate for the limitations of lower-grade bentonite, allowing for the formulation of drilling fluids that meet the demanding requirements of diverse drilling conditions.

They compensate and contribute to the overall efficiency and success of drilling operations. As a result, the drilling side of our industry has evolved, and as such, the industry must adapt to these additive-added polymers to ensure responsible and effective well development.

Today, a comprehensive understanding of well development, encompassing both evolving chemical and mechanical methods, is critical for optimizing well performance and safeguarding groundwater production.


Michael Schnieders, PG, PH-GW, is a professional geologist serving as the principal hydrogeologist and president of Water Systems Engineering Inc. in Ottawa, Kansas. Schnieders’ primary work involves water resource investigation and management, specializing in the diagnosis and treatment of fouled well systems. Schnieders served as the Groundwater Foundation 2017 McEllhiney Distinguished Lecturer in Water Well Technology. He can be reached at mschnieders@h2osystems.com.


 

Edd Schofield is the technical sales manager–chemicals for Johnson Screens and has been with the company since 1988. He served as the Groundwater Foundation’s McEllhiney Distinguished Lecturer in Water Well Technology in 2007. He can be reached at edd.schofield@johnsonscreens.com.

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