Well Development and Rehabilitation Methods

A personal update.

By Ed Butts, PE, CPI

Most of what I am about to espouse is based on my personal experience. In no way am I inferring there are
not other, better, or alternative well development and rehabilitation methods that will yield similar or better results.

Well rehabilitation and development procedures are often tailored to a contractor’s experience and background along with the aquifer and well-specific characteristics. Therefore, I will review in this column many of the old methods plus advancements to well rehabilitation and development that have occurred during the past half-century.

Methods in 1975 to 2025

Many of today’s still-functioning wells that were drilled in 1950 were 25 years old in 1975 and are now 75 years old. Unfortunately, many well owners and operators believe well systems to be a permanent and tangible asset with an unlimited service life.

This substantially changes the approach to well service, increases the risk of performing any rehabilitation, and trying to salvage a well that most likely should be replaced.

As I continue to advance in age, I am still working with wells drilled in the 1950s and 1960s and some I personally designed 45 years ago. I am starting to wonder how long they will last, and if I will be the one who designs a replacement well for one I originally designed in 1980 or so. In fact, I have already designed a few.

As far as applying well development and rehabilitation techniques are concerned, I learned more over the years from what didn’t work so well or totally failed. However, one thing that hasn’t changed much in 50 years is the nature of clients. We were and still are often limited to a fixed cost or time budget for well service work as clients are always cautious about spending their money on what many regard to be an unnecessary and uncertain process to begin with.

As a response, our industry has had no choice but to become more knowledgeable and capable of performing new techniques of well rehabilitation and development along with the tried and true.

This means most contractors are now taking a more measured and scientific approach to well rehabilitation and development that was done in 1975, while many other elements of the water well industry are not markedly different.

Thus, most advancements and improvements in well development and rehabilitation have been slower and more deliberate and largely based on known and proven sciences of well hydraulics, corrosion, and encrustation.

Obviously, there have been numerous additions to chemical methods and some physical well development and rehabilitation procedures as well, but for the most part many of the newer methods are actually the brainchild of a water well contractor from decades ago as well as an extension and refinement of past methods. Thus, most of the methods fundamentally practiced 50 or more years ago—such as well swabbing, surging, bailing, airlifting, and jetting—remain in widespread use today.

Although considerable research and refinement in aquifer and well hydraulic theory and science has been conducted, the basics have not changed too much over the years since Darcy’s law still applies. Therefore, what was practiced and effective in 1975 is typically just as viable and effective today for the most part.

Unfortunately, some development and rehabilitation techniques are still stubbornly used in situations where more recently developed methods and procedures would produce better results. Other old timers and I have a distinct experience advantage over most of those under 40, as we can recall the methods we used that worked and didn’t work in well development and rehabilitation 50 years ago.

At the time I was personally involved in the construction of domestic, irrigation, and municipal water supply wells, and we used several methods tailored to the specific construction type of the well, proposed service, and aquifer type in our area. In those days many wells in our region, particularly smaller domestic and irrigation wells, used Star or Mills-Knife perforated well casing rather than screens in alluvial formations.

In most cases, the use of a well screen was reserved for high value, larger capacity engineered wells, such as those for municipal or industrial uses.

This often resulted in well development becoming difficult and time consuming, particularly using jetting techniques, as most of the imposed energy ineffectively and harmlessly bounced off the casing’s interior wall with minor penetrating of the formation.

Generally, for a new well, well efficiency was a second and minor consideration as increasing yield while limiting sand production was the main objective. This meant using repetitive and incremental swabbing, surging, airlifting, and bailing techniques, which generally yielded the best results as this action permitted
marginal two-way flow through the reduced openings.

Another change in well development is due to the increased use of bentonite clays and polymers during well construction. These constituents modify the chemical balance and can impact the effective breakdown and removal of mud cakes. There were limited chemicals used in 1975, primarily for the breakdown of drilling muds and filter cakes, especially when mud and reverse circulation rotary methods were used to drill the well.

However, the percentages of phosphate and phosphorus levels in drilling fluids have risen dramatically since 2000, often resulting in more difficult and demanding well development processes. Thus, well drillers and engineers have had to become more knowledgeable in chemicals and chemical neutralization. Therefore, for total effectiveness, modern well development should incorporate both physical and chemical
methods.

In addition, although the regulations were not as strict in 1975 as they are now, dynamite would occasionally be used to open consolidated and semi-consolidated boreholes such as basalt, sandstone, and shale. Finally, a reliable procedure for deactivation of spent chemicals and pH rebalances, along with a safe site for disposal of pumped water, was often problematic, if considered at all.

Advances and Changes Since 1975

Chemical encrustation is the deposition of minerals on the well screen or gravel pack, which restricts the movement of water into a well. Chemical encrustation is caused by the precipitation of minerals dissolved in the groundwater due to changes in flow or pressure conditions at the well.

Water well encrustation typically consists of iron and manganese oxides, calcium and magnesium carbonates, or sulfates. Chemical treatment of good candidates of wellbores can often recover most, if not all, of the lost production, but the program should be conducted using a measured scientific and diligent approach.

In my opinion, there are three primary current causes of water well production decline necessitating well maintenance or rehabilitation:

• Physical or mechanical: Sand, silt, clays, or formation/aquifer particle well screen/bore blockage
• Geochemical or geothermal: Oxidized iron, manganese, calcium carbonate, etc. from cold or hot water
• Biochemical (biofouling): Iron, sulfurous, or manganese bacteria; organic or gelatinous slime, etc.

Obviously, there are subcategories to each group, but from my experience, one of the previous three causes is usually the dominant culprit.

Well blockages and decline in yield can also be related to the use of the well. Formation blockage caused by solid particle invasion and migration is often the main reason for a decline of geothermal reinjection capacity, especially in the weakly consolidated formations such as shale or sandstone.

This often requires a unique approach to rehabilitation. Without question, two of the primary advancements to water well rehabilitation since 1975 are the plethora of scientific research and widespread use of downhole video cameras to observe and identify various causes of well decline.

These include identification of the various physical, bacterial, and biological causes of well plugging and possible solutions. Before 1975, most of the methods and procedures used for well rehabilitation were based on so-called trial-and-error methods employed by previous generations of well drillers passed down to the current generation. Many of these worked or marginally worked while some did not work at all.

Downhole Video Cameras

Water well video camera inspection systems were in their infancy in 1975 and mainly consisted of grainy, down-viewing black and white images—lateral views were rare. The introduction of color images and lateral views beginning during the 1980s and into the 1990s greatly increased the value of well video inspections.

In addition, more firms began to offer these services, which prompted competition and lowered costs. The advancement in technical knowledge as to the cause and mechanism of wellbore and screen blockage, combined with the ability to view an actual video of impacted well sections, now provides the well contractor and owner with a scientific approach to well maintenance and restoration to what was once viewed problematic or unsalvageable wells.

These technologies include sonar jetting, well jetting, impulse generation, chemical treatment using specialized tools for placing and removing chemicals in precise locations, and installation of suction flow control devices within the existing well.

A principal advantage in well rehabilitation since 1975 is the ability to conduct a forensic examination of the root causes for a specific well’s decline before embarking on a remediation process. Conducting comprehensive water, corrosion, and scale analyses, combined with a specific capacity pump test (Figure 1) and downhole video survey, provides great insight into the present condition of the well structure and the location of various fouling or plugging mechanisms.

These advances have also changed the way we respond to different problems. Although many of the methods of well rehabilitation remain in use, there have been substantial additions to both physical and chemical methods since 1975.

Well Rehabilitation Methods

The predominant newer physical well rehabilitation methods introduced since 1975 are modified well brushing methods, hydrofracturing (hydrofracking), impulse generation, sonar and well jetting, carbon dioxide injection, and air burst technologies. I have personally used some of these new methods on a client’s well at one time or another and have found them to be efficient and effective when used in the proper application, procedure, and location.

Before around 1990, wire brushing of well casings or screens often used split and unwound strands of steel wire rope. Unfortunately, the splayed cable ends would often cut into softer steel surfaces or miss particularly scaled regions, resulting in unscraped surfaces or scrapings that can increase slot sizes or damage screens, worsen corrosion rates, develop iron bacteria, and transfer iron and/or manganese from the well structure.

As a result, the alternative use of stiff plastic brushes specifically developed for well use (Figure 2), diversely constructed using close spacings of nylon or polyethylene fiber strands, are typically preferred to limit the occurrence of possible damage to the well structure.

Hydrofracturing

The process of hydrofracturing (Figure 3) consolidated (hard rock) and semi-consolidated formations has proven to be a successful method for restoring lost production in older low-producing wells, and in many cases, enhancing the production of new wells. It is generally used as a replacement method for dynamiting, which was often used to open consolidated and semi-consolidated boreholes during the 1980s and before.

The technique involves injecting high-pressure water through the well into the rock formations surrounding it. Hydrofracturing may open or widen fractures in the bedrock and extend them further into the formation, contacting previously unavailable fissures or fractures. This may increase the network of water-bearing strata supplying water to the well.

Hydrofracturing was originally developed to increase oil and gas well production and has now been adopted as a technique used by the water well industry. Many firms have been established that specialize in hydrofracturing, and in most states, the work can only be undertaken by a licensed or registered water well contractor.

All drop pipe, drop cable, pump and motor, and other equipment within the well must be removed to begin the process. The procedure then involves lowering one or two inflatable hard rubber packers on a string of pipe downward into the wellbore. The packers are usually set a minimum of 20 feet below the end of the casing and 60 feet below ground. The packers are thereafter inflated using vegetable (food grade) oil
or air to prevent borehole and aquifer contamination and to seal off a section of the well’s open borehole. Water is pumped at high pressure into the section of the well between the packers, or below a single packer if only one is used.

Most hydrofracturing equipment for domestic wells can provide between 500 to 2000 psi of pressure, although up to 3000 psi can be developed in some cases. An injection pumping rate of up to 50 GPM is usually adequate for injecting water into the well. The water is injected into and through the tight or sealed-off fissures and fractures, which reestablish the borehole’s connection to the aquifer. Some states have specific regulations, limitations, and permit requirements relating to the hydrofracturing process.

An indication of successful hydrofracturing is a sudden drop in the injection pressure, indicating that the surrounding formation is accepting water at a higher rate. Depending on the well and aquifer type, the process is generally repeated, up to five times in some cases.

All water used for hydrofracturing must be clean, free from air, and potable to prevent air binding of the formation and contamination of the surrounding aquifer and neighboring wells. Anecdotal information claims water used in hydrofracturing can migrate to adjacent nearby wells, potentially resulting in contamination and place undue pressure on underground faults, increasing the risk of local seismic events,
but this is currently speculative and has not been verified for water wells.

Impulse Generation

Use of a high-pressure, non-reactive gas, such as nitrogen, creates impulse generation and a resultant percussive wave (Figure 4). These are methods used to generate rapid and high-energy pulses downhole and is another means of mechanical cleaning.

Just as with other methods, the nature of fouling, the degree of impact, and the structural integrity of the well must be known. Gases are employed in one of two manners; they can be used to create a bubble that when collapsed creates a percussive wave causing a mechanical shock to the well. A second means is to use the gas to create secondary reactions, including a weak acid generation.

In recent years, owners have found that new impulse generation technology is more cost effective and efficient than alternative well rehabilitation techniques alone. The impulse generator, equipped with a pressurized hose and valve system, is positioned in the well screen or water-producing zone. Once in place, the operator releases impulses of high-pressure nitrogen in short, repetitive bursts.

Through controlled release of compressed nitrogen, the generator produces an elastic impulse and a secondary expansion of gas bubbles, causing a pressure wave that moves laterally through the screen into the well’s gravel pack and adjacent formation. Expansion of compressed gas creates an airlift effect and vibrates and loosens mechanically plugged sediment and biological deposits from the screens and surrounding aquifer.

Typically, the impulse generator is used in tandem with other mechanical methods such as brushing, surging, jetting, and isolation pumping by a drilling/pump contractor to remove loosened sediment, scaling and deposits, and biological growth. The released energy can penetrate several feet beyond
the well screen, enabling contact with cemented materials and encrustation far beyond the wellbore, making for an efficient and effective process.

I have been involved in three well rehabilitation processes using impulse generation, all of which were successful to a certain degree. The most recent application occurred in a 20-year-old, 12-inch, 330-foot municipal well in cemented sand and gravel with extensive screening. The available production before rehabilitation amounted to less than 400 GPM with a specific capacity of 5.33 GPM/foot of drawdown, while the tested yield after rehabilitation rose to more than 1000 GPM with a specific capacity of 13 GPM/foot of drawdown—an improvement of 244% and a full restoration of the well’s original yield.

This is not to say that impulse generation is applicable to all wells and situations. The force created by the suddenly released energy can be potentially injurious to older or fragile wells with weak or inadequate structural elements, such as deteriorated casing or screens. It should be used with prudent caution and consideration of all aspects of the well and aquifer.

Jetting

AirBurst™ (Figure 5) from Airburst Technology LLC is a patented process that uses high-pressure air or inert gas to stimulate selected zones within the formation by generating high-energy pressure pulses in the well. This energy generates acoustic waves that break up and remove mineral scales, silts, sedimentation, and biofilms from the borehole wall or well screen.

With the energy being released at 15/1000 of a second after firing, it generates an air bubble that expands and collapses inside the well. This provides an intense surging action that generates a mechanical cleaning of the well as the bubble expands and collapses. As the bubble collapses, it creates a negative pressure zone in the well that draws mineral and biological debris from the formation during the process for easy removal with a bailer.

Sonar-Jet (Figure 6) is a patented process which uses a custom-fabricated detonating cord that produces a slower burn rate and has a greater gas-producing capability than a standard detonating cord.

Sonar-Jet works by using a mild harmonic frequency of shock waves to disintegrate mineral and bacterial deposits. The detonating cord has a series of pressure compensators to produce a 100-millisecond delay at each compensator point, creating a water pick effect while pulsing the water at a high velocity back and forth through perforations to deep clean the productive aquifer.

Sonar-Jet can be used while chemicals are in place, pulsating them deep into the formation or swabbing afterward to help re-consolidate gravel packs. Sonar-Jet often increases specific capacity to 100% to 200% of its original condition and has improved some yields in excess of 400%.

Another jetting process, WellJet, is also used to rehabilitate wells. WellJet utilizes highly pressurized water in a laminar flow to remove obstructions from the screened/perforated area, filter/gravel pack, and adjacent formation to break up the harmful deposits that cause inadequate well performance.

The carbon dioxide (CO2) Aqua Freed process uses an injection of liquified and gaseous carbon dioxide placed into the well. Pound for pound, carbon dioxide develops as much energy as high explosives and is much safer to use.

Gaseous and liquid carbon dioxide contains tremendous energy, which results in the detachment, dissolution, and removal of sediments and encrustation from the surfaces within the well screen and surrounding aquifer. It is effective at removing mineral incrustation, biological fouling, and physical plugging. It’s environmentally friendly with no adverse chemical waste stream.

Dry ice (solid carbon dioxide) has also been used throughout the years to generate carbon dioxide gas for water well rehabilitation. The gas dissolves into water to form carbonic acid (H₂CO₃), a powerful acid. Placing a packer directly above an affected zone causes the cold steam to travel out from the well and into the area surrounding the well where it freezes.

Freezing water expands up to 9% with a hydraulic force that can reach up to 30,000 psi. The pressurized carbonated dioxide pushes out into the formation and dislodges scale in both the screen, filter pack, and aquifer. By using an isolation packer with carbon dioxide, the combination becomes a powerful way to clean and rehabilitate water wells without using or releasing toxic chemicals.

Chemicals

Chemical well development and rehabilitation typically includes the use of a single or multiple chemicals to break down drilling fluids and dissolve encrusting scale and materials. The primary advancement in chemical treatment of water wells since 1975 is the increased knowledge of well plugging causes and mechanisms, allowing formulation and implementation of a tailored approach towards remediation.

The use of high levels of chlorine, specifically sodium hypochlorite, is often needed to facilitate the oxidation and breakdown of bentonite clays and polymers from a new well during development. Acids, particularly mineral acids, are used to dissolve mineral-based precipitates such as calcium carbonate, sulfate, silicates, magnesium hydroxide, and mixtures and are also highly effective on iron and manganese oxides.

Of those listed, carbonates are often the most common and most easily dissolved with the resulting release of carbon dioxide gas. A simple example is the action of hydrochloric acid on calcium carbonate deposits.

The most common and useful mineral acids used in water well rehabilitation are hydrochloric, muriatic, phosphoric, and sulfamic. The use of polyphosphates, acids, surfactants, polymers, and other chemical formulations along with physical agitation and dispersal has been successful in many cases towards improving well performance due to mechanical or geochemical-induced blockages.

Fine-grained soil materials can be dispersed by polyphosphates and surfactants. Surfactants are a group of chemicals called surface active agents that can reduce the surface tension of water and allow particulates to move more freely within the formation’s pore space.

Modern science has also provided the ability to formulate and blend custom chemicals to target specific contaminants and well conditions. For decades, the use of high levels of chlorine was employed to dissolve scale as well as disinfect the well’s interior surfaces. However, these extreme chlorine concentrations in many cases often did more harm than good as damage to soft metals and rubber compounds often resulted.

Later, strong acids were often used. Once again, the results were often mixed or insufficient, particularly if the acid was unable to penetrate and dissolve the layered scale or deposits outside of the well.

The best water well improvement results are typically achieved by initially conducting a complete water chemical analysis followed by a properly selected and balanced combination of procedures, including physical and chemical methods.

In recent years, in response to a growing awareness of biological and environmental hazards, many new water well treatment chemicals and associated products have been introduced to comply with the NSF-61 standard to foster green recognition as an environmentally safe chemical. Currently, in many states and
localities, chemicals used in water well treatment must comply with NSF-61 for use in a potable water supply well. In most cases, physical and mechanical techniques such as wire brushing, swabbing, jetting agitation, and surging should be initially used to expose the offending scale and reduce the chemical demand.

To summarize, technology to rehabilitate and develop water wells continues to evolve and undoubtedly will for the foreseeable future. I’m sure I have just scratched the surface as I may not know about many other innovations as they are the direct result of the imagination and experimentation by well contractors and chemical treatment creators and vendors.

We will continue this series next month with a review of the advances made to water pumping and system technology.

Until next time, work safe and smart.

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Ed Butts, PE, CPI, is the chief engineer at 4B Engineering & Consulting, Salem, Oregon. He has more than 40 years of experience in the water well business, specializing in engineering and business management. He can be reached at epbpe@juno.com.