It may not be exciting, but it is among the most important steps of completing a new well.
By Gary Gin, RG, and Michael Schnieders, PG, PH-GW
Inadequate or insufficient well development can have negative consequences to a well’s performance over its life cycle.
Whether the well is a standard production well or an aquifer storage and recovery (ASR) well, poor pump and recharge efficiency can lead to increased clogging and lowering of pumping water levels.
Inadequate development impacts well efficiency, which requires more energy per gallon pumped than an efficient well. Even a small impact in energy costs per gallon can mean a significant cost burden to the water provider over the life of the well. And this problem is magnified in deeper pump settings because the energy to lift groundwater to the surface is costly.
Well development is often used to describe the final stages of new well construction, a maintenance activity, or a rehabilitative effort on an existing well.
For a standard production well, an ASR well, or even an environmental well—cleaning the borehole, maximizing efficiency, and stabilizing the borehole-aquifer interface are common goals for development. The effective completion of these goals can set the tone for a new well, not only from an operational efficiency standpoint but also from a water quality view.
Often misunderstood is the role that insufficient well development can play in water quality. Restricted or blocked flow—common elements in a poorly developed well—can result in hydrologically isolated zones within the well. This isolation often results in the development of reducing environments, areas which favor the development of anaerobic growth.
In addition to nuisance organisms such as sulfate-reducing bacteria, many environmental coliforms take up residence in these areas. As long as the flow profile remains affected, the anaerobic presence can continue to impact produced and injected water quality despite even the best disinfection efforts.
Use of Drilling Fluids
Drilling fluids, commonly referred to as muds, are used to prevent borehole collapse, reduce friction and heat at the drill tip, and aid in the suspension and removal of cuttings during the drilling process.
The muds used in water well drilling begin with water, and then clays and other chemicals are incorporated into the water to create a more uniform blend to overcome challenges specific to that site. The clay component is typically a combination of formation clays and processed or refined clays such as bentonite. When wet, clays expand to several times their dry mass, which, in addition to their colloidal properties, likewise create a self-sealing mechanism which acts as a barrier to permeability.
A variety of chemicals are added to the muds depending on the formation, drilling process, groundwater quality, depth, and length of time spent drilling. These additives are used in the drilling process for a number of reasons. Some of the goals of these additives include pH control, enhanced sealing of permeable layers, increased borehole stability, mobilization of sediment, prevention of lost circulation, improved viscosity, and to minimize formation damage.
Part of the well development process is to remove the introduced drilling fluids and develop a more normal flow pattern from the aquifer into the borehole. Two types of additives that can challenge the well development procedure include polyphosphates and polyacrylamides. These two polymers are used to enhance clays (natural and processed) during the drilling process.
Polyacrylamides are a type of linear chain polymer that are highly water absorbent. Polyphosphates are larger, linear chain or cyclic ring structures with a negative charge that bond readily with many natural elements such as calcium, magnesium, and iron.
Polyacrylamides and polyphosphates are resilient polymers, maintaining their structure and bonds over a long period of time. As the polymers degrade slowly over time, minor phosphate residuals are released into the well, oftentimes resulting in macronutrients or stimulants for microbial activity.
The resiliency of these additives is one reason that multiple methods for development are often encouraged. At a minimum, mechanical and chemical methods are advised to combat the physical and chemical properties of the drilling fluids.
Additive manufacturers typically recommend using 100 to 200 mg/L (parts per million) chlorine to aid in the breakdown of the polymers. Laboratory research and field studies have shown that at a minimum 1000 mg/L is required to oxidize and create the disassociation required for these polymers to begin to break down.
Additionally, specifically using sodium hypochlorite as opposed to calcium hypochlorite helps to limit the calcium bonding that can occur, which limits the polymer degradation. It is generally advised to use a range of 1200 to 1500 mg/L sodium hypochlorite to degrade the polymer additives prior to traditional well development efforts.
Chemical parameters that can be assessed to identify the presence of legacy or remnant polymers include orthophosphate, polyphosphate, total phosphate (as PO4), total reactive phosphorus, hydrolyzable phosphorus, acrylamide, and the presence of microplastics. Additionally, microscopic evaluation can aid in the identification of the polymers from a physical standpoint, oftentimes providing introspection into the agglomeration of these polymers and formation sediments.
During this oxidative treatment, timing is not as critical as it is for disinfection. However, sufficient time and agitation are recommended to ensure distribution throughout the borehole and well screen interface.
A Case Study
LRE Water, Water Systems Engineering Inc. (WSE), Johnson Screens, and Roscoe Moss Co. conducted collaborative research efforts to better understand the impact that this strong oxidation effect would have on steel well components (Phase 1) and on residual muds (Phase 2).
It was identified that the prolonged exposure (beyond 96 hours) of chlorine to the well structure would have some detrimental effects and could accelerate corrosion rates. While each well site is unique, our findings indicate that older wells (5 years and older) subjected to high chlorine dosage (more than 1000 ppm) should have a contact time between 24 and 48 hours to minimize any corrosion impacts to the stainless steel components.
Following treatment, steps to evacuate the well of residual chlorine (airlift pumping) should be taken. For newly constructed wells, high chlorine dosages (more than 1000 ppm) impacting stainless steel well screens may not be as much of a concern. This is because newly constructed wells are still full of fresh drilling mud which consumes the high dose of sodium hypochlorite quickly. Residual muds and the chlorine residual significantly reduce within a 24-hour period, which is not long enough to impact stainless steel well components.
To better understand the signatures from drilling fluids, two mud samples were submitted to the WSE laboratory for evaluation. The first sample was 12 years old and had been preserved in a sealed container since collection at the time of drilling of a municipal water supply well in 2010. The second sample was collected while a new water supply well was being constructed in March 2022. The data from the two samples is presented in Table 1.
While some settling had occurred in the older mud sample, reducing the amount of dissolved solids in the liquid port
ion, the presence of polymers remained strong. Additionally, the old mud sample remained oxidative and contained an active microbial population as determined by Adenosine Triphosphate (ATP) analysis.
The new mud maintained a strong alkaline signature with a high load of dissolved solids which remained in suspension. As with the old mud sample, the new mud exhibited a strong polymer signature.
The mud samples were subjected to macroscopic and microscopic evaluation following centrifugation, a process that separates solids suspended in liquids for better evaluation. Microscopic evaluation of the new mud confirmed the presence of polymers creating a uniform composition of polymer, clay, and formation sediment.
Settling over time of the formation material, clay, and polymer was evident in the water chemistry and in the macroscopic evaluation of the old mud sample. However, the polymer remained viable (cohesive and resilient).
Restricted or blocked flow—common elements in a poorly developed well—can result in hydrologically isolated zones within the well.
In addition to the high dosage of chlorine for oxidation and destruction of the polymers, use of clay dispersants is recommended coupled with mechanical agitation (e.g., dual swab assembly), to enhance development efforts. Clay dispersants, such as NW-220 by Johnson Screens, help to destabilize the bentonite and formation clays further once the polymer additives have been broken down by oxidation. Mechanical energy such as surging, jetting, airlifting, and to a certain extent over-pumping, can further aid the process.
Keys to Success
The key components to a successful well development include the culmination of these four phases: time, planning, energy, and monitoring.
The time required to develop a well will be site specific and must be weighed with practicable parameters of success established and agreed upon before drilling begins. There is no set time per foot of completion or method of drilling.
For planning, measures should be taken to identify the scale and magnitude of the well development needed, so that proper communication can be coordinated with the drilling contractor. This planning effort can streamline the development process and avoid logistical hurdles (e.g., smart development versus longer development).
For any of the chemical or mechanical efforts to be successful, sufficient energy must be available for the physical application and dispersal of the chemicals and energy downhole. While the chemicals can break down the additives and help destabilize the clays, physical energy is required to mobilize and evacuate the components.
Finally, monitoring of operational efficiency and water quality throughout the effort provides a good benchmark of success. Clear water, or the lack of visual turbidity, is an insufficient indicator of sufficient development. The images shown with this article all relate to this.
While important, those visual parameters should be verified by field tests to include conductivity, pH, oxidationreduction potential (ORP), and specific testing for any additives used.
As the nature of groundwater use changes and we as an industry are faced with more challenges with regards to production, recharge, and water quality—recognizing and acting with a better understanding of the importance of development is essential.
For successful well development, there should be clear expectations as to the responsibilities and objectives of the effort. Methods should be discussed and approved with benchmarks established ahead of time with all parties participating in the discussions.
It can be said that well development is not the most exciting part of the well construction process, but it is arguably the most important step of completing a new well and achieving sustained and consistent well performance.
Gary M. Gin, RG, is the vice president of Arizona operations and the ASR practice lead for LRE Water in Phoenix, Arizona. He has 24 years of extensive experience in water resources planning, recharge systems, and water supply development. He can be reached at Gary.Gin@LREwater.com.
Michael J. 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’s 2017 McEllhiney Distinguished Lecturer in Water Well Technology. He can be reached at firstname.lastname@example.org.