Groundwater is the portion of the water cycle that is collected and stored in the soil or aquifers under the earth’s surface as a result of precipitation.
Groundwater is considered a huge freshwater source.
Throughout human history, people depend largely on groundwater as a source of fresh water because it’s clean, easy to access and doesn’t need further treatment.
As the population rises and water pollution, it is no longer acceptable to rely on shallow groundwater.
That is why water wells are required to access deep clean groundwater.
Several factors must be considered before drilling a water well.
As it will not be an easy mission to drill a well that is renewable and last as much as possible.
Choosing a location and digging a well
Choosing a location for a well will be the first step.
In a place like Rapaura, where groundwater is typically available everywhere, finding an aquifer is simple.
Water availability is significantly more unpredictable elsewhere, therefore a well owner should conduct some preliminary investigation.
There are also several practical issues, such as power supply, agricultural or irrigation system position and keeping a safe distance from adjacent wells.
The diameter of the well casing is the next decision to be taken.
The diameter of the well has a minimal bearing.
The casing diameter is often set to match the required pump size while still allowing for efficient operation.
This implies reducing friction losses in the annulus, the gap between the casing and the pump, or the delivery line to the surface.
The well becomes more costly as the casing diameter increases.
This reflects the increased cost of bigger steel pipes as well as the longer drilling procedure.
Once the location has been chosen, there are a few things to consider, such as how deep to drill and which construction type to utilize.
The percussion technique is used in many shallow or exploratory wells to produce the finest samples for defining subsurface geology or because it is reasonably inexpensive.
When precise information is needed to choose where to install the screen and the most efficient slot size in the public water supply or test wells, the MDC frequently uses this method.
However, for wells deeper than 15 meters, the percussion approach is too sluggish.
A speedier approach, such as rotary drilling, is utilized in this scenario for private good owners who care more about discovering if a viable water-bearing stratum exists.
Methods of Well Construction
Percussive drilling/cable tool
The cable tool method is the oldest and is an adaption of a method for drilling holes that have been used since ancient times.
The percussive method entails repeatedly raising and lowering a massive chisel-shaped tool weighing several tones into the same hole.
Each time, the tool is twisted to make a circular hole.
Following that, the crushed debris is bailed to the surface. Water is poured into the hole to create a slurry that allows the cuts to rise to the surface.
The cutting tool is normally one meter long and is fastened to the drill stem or tool, which is made of hardened steel.
This adds weight to assure the hole’s vertical alignment.
A steel cable that crosses over the top of the mast or derrick connects this to the drill rig.
Cuttings collect as a watery mixture at the bottom of the hole throughout the drilling operation and are retrieved by a basic bailer consisting of hollow tubing with a non-return valve at the base.
A sand pump is what this is called.
On the end of another cable, the bailer is lowered down the well, filled and then lifted back to the surface to be emptied.
To prevent the rock from collapsing in and plugging the well, the casing is then forced downwards.
The leading edge of the casing at the bottom of the well is protected from fraying by a hardened steel shoe.
The top of the current length in the ground is welded with a new piece of casing.
Because the hole must be cased with consolidated material to prevent collapses, the cable tool approach is a slow process.
Triple welds are utilized to ensure that the connection does not break during the drilling operations.
This approach has these advantages:
More precise formation sample and tracking
less water uses
The simplicity of maintenance.
However, the cable tool method’s drawback:
Its slow rate of advancement.
As a result, it is restricted to depths of roughly 50 meters. Because the hole must be cased
This procedure is slow.
Rotary drilling
The drill bit is rotated in a circular motion to carve a round hole through the sediments in this technology, which was designed for drilling oil wells.
The rotary system, unlike the cable tool approach, which combines periodic up and down motion with twisting, is a continuous operation.
As the hole deepens, drilling is only interrupted to add casing or add further rods.
The rotary drill bit is more difficult to use than the cable drill bit.
The drill bit at the face of the hole is connected to the rig at the surface by a series of hollow pipes known as rods.
Its main benefit over the cable tool approach is speed, with a 30-meter deep well bored in less than a day.
A circulating fluid travels downward within the drill rods, out through the bit and then back up the annulus between the exterior of the drill rods and the hole in the rotary technique.
Drilling fluid keeps the hole’s interior wall pressurized.
It also cools the drill bit and removes the cuttings.
Depending on the situation, special additives may be utilized.
They’re used to adjust the viscosity of drill fluid.
The introduction of the top drive, which allows the casing to be pushed at the same time as the hole is drilled, resulting in a more seamless drilling operation, was a significant advancement.
For commercial well owners, the air rotary approach is the most efficient and cost-effective.
A percussion rig is used to drill a big diameter hole closest to the surface, followed by a rotary rig drilling a smaller diameter hole inside this.
Other methods
There are other methods to drill wells that are not common such as:
Digging: This method Is used for shallow wells and in unconsolidated glacial and alluvial aquifers.
Boring: this method uses a simple auger that can be hand-operated or power-driven to bore well in shallow and unconsolidated aquifers.
Driving: these wells are only available in unconsolidated formations that are largely free of cobbles or boulders, where a series of connected lengths of pipe is driven into the ground by repeated hits below the water table.
Jetting: in this method, a chisel-shaped bit attached to the lower end of a pipe string is used where nozzles are located on each side of the bit.
Water Well Disinfection
Before being used, every water well should be cleaned and disinfected to guarantee that any hazardous bacteria or viruses generated during construction are eradicated and that future sampling of the well’s water quality is indicative of the aquifer conditions.
Simple chlorination, shock chlorination and bulk displacement are all procedures used to disinfect water wells.
Well worsening
The causes of well worsening are frequently classified as follows:
This is caused by naturally occurring microorganisms that filter both organic and inorganic elements from the water.
Mineral encrustation occurs when minerals are mostly oxidized by oxygen seeping down the good column during operation, resulting in an oxidized zone surrounding a working well.
This zone promotes biological growth and a large volume of plugging deposits from biologically filtered minerals trapped in the biofilm growth for protection.
Iron, manganese, calcium, magnesium and silicate are the most commonly found minerals.
Formation damage occurs when fines (sand, silt, or clay) from the formation invade the near-well environment and some of the pore spaces surrounding the well collapse.
Wells maintenance
During the typical aging process, most wells encounter some form of operating issue.
Many factors, including water chemistry, aquifer features, operational schedules and well construction specifics, might influence how quickly a well experiences such difficulties.
Some typical issues include loss of production, discoloration at commencement, changes in water quality, bacteriological failure, increased operating costs, lower life expectancy and increased life-cycle costs.
The time-based approach is critical to the well health because waiting until issues arise frequently means it is too late for a maintenance cleaning to be successful, and more expensive rehabilitation will be required.
Rehabilitation frequently necessitates the removal of pumping or injection equipment, as well as rigorous cleaning treatments to remove deposits.
Maintaining peak efficiency; maintaining the lowest cost of pumping water; maintaining the maximum production rate; minimizing failure of total coliform positive samples and elevated heterotrophic plate counts; preventing discoloration on startup; preventing many tastes and odor issues, and maintaining the original water quality by maintaining the original production profile are all advantages of keeping a well clean.
References
[1] Well Construction and Compliance, [online] Available at:https://www.oregon.gov/owrd/programs/gwwl/wcc/pages/default.aspx
[2] Water well construction, [online] Available at: http://igi.ie/assets/files/Water%20Well%20Guidelines/Guidelines.pdf
[3] Royal Melbourne Institute of Technology (RMIT). Manual of Australian groundwater practice Well Construction Methods, [online]
[4] Construction of Wells: 7 Methods, [online] Available at: https://www.biologydiscussion.com/irrigation/well-irrigation/construction-of-wells-7-methods/73212
[5] Well-Timed Maintenance [online] Available at: https://www.wqpmag.com/groundwater-treatment/well-water-treatment/article/10955842/well-timed-maintenance
