What is the Advantage and Disadvantage of Well Drilling Rig

Contributed by Stephanie Evans, Staff Geologist, PPM Consultants

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There are several well drilling methods that can be used, and choosing the best option for your specific situation will depend on several factors. Let’s take a closer look at the advantages and disadvantages of some popular drilling techniques to determine which might be the best option for your project.

Auger Methods: Augers have the appearance of a screw, where the screw threads (flights) carry the materials to the surface through the rotation of the drill stem.  The bottom of the drill stem is equipped with a bit to help the auger advance into the ground. This method is useful in relatively shallow unconsolidated soils.

1. Flight Auger (Solid Stem): Typically utilizes a Claw Bit to advance solid stem auger flights into the ground. The drilling equipment applies pressure against the top of the stem while turning it into the ground where the bit displaces the soil and moves it up the flights as the drill goes deeper into the subsurface.

Pros: It does not require circulation fluids, which makes site clean-up easier than some other drilling methods. The rapid drilling into soils with a lot of clay can save time and money.

Cons: The augers must be removed and sampling done in an open hole, therefore, it is not appropriate for sampling materials (loose, sandy soils) that will cave in when the augers are removed. It does not do well below the water table due to water infiltration.

2. Hollow-Stem Augers: This type of drilling is similar to solid stem, except the Claw Bit is attached to a hollow stem, instead of a solid one. Flights are attached to a hollow rod that is sized to sample through the middle of the rod. There is a removable plug/bit to allow the sampling to be done without removing the drill stem. Once the borehole reaches the desired depth, the hollow stem acts as a temporary casing, keeping the side of the borehole from caving in.

Pros: It allows for uncontaminated sampling in formations of unconsolidated soils. Since drilling fluids are not generally used with this method, there is no interference with the groundwater quality by the introduction of fluids into the borehole. It can be used to sample water quality at varying depths as the boring is advanced. Hollow-stem augering excels in non-cohesive soils such as sand and gravel. Rapid drilling into soils is relatively easy and cost-effective.

Cons: It cannot penetrate cobbles, boulders, and most rock formations. Its use is limited in loose, sandy soils where water table infiltration can contaminate sampling (sampling in loose soils requires alternate sampling equipment like a split spoon). Another challenge when using hollow-stem augers is trying to drill with flowing sands. Flowing sands is a term that drillers use when referring to a mixture of fine sand and water that infiltrates drilling equipment. The flowing sands can rise upward in the hollow-stem auger and prevent a driller from obtaining an accurate sample.

Direct-Push Methods: Direct push technology, often referred to as DPT, uses the weight of the static drill rig combined with a hydraulic/percussion hammer to advance sampling and logging tools into the subsurface.

Pros: DPT is commonly used in the remediation field due to its small footprint and versatility. It can rapidly and cheaply obtain samples and information in borings. It works well for unconsolidated materials. Essentially no drill cuttings are generated by direct push methods. This reduces the potential for worker exposure to hazardous contaminants relative to traditional rotary drilling techniques, as well as minimizing the generation of potentially hazardous waste during site investigation.

Cons: DPT is typically only useful at generally shallow depths and in unconsolidated formations. DPT is not suitable for formations containing large or excessive gravel, cobbles, and boulders or for bedrock drilling due to the lack of augering capabilities.

Rotary Methods: For rotary methods, borehole advancement is achieved by the rapid rotation -utilizing high levels of torque and rotation- of a drill bit that is mounted at the end of the drill pipe.  Cuttings are then brought to the surface by the circulation of drilling fluid (drilling mud, water, foam, or air). The rotary methods are typically appropriate for deep boreholes in rock formations and can be used in both unconsolidated and consolidated materials.

1. Air Rotary: Air or foam is used through the drill stem to bring the cuttings to the surface around the outside of the drill stem.

Pros: It can be used to great depths (approximately 1,000 feet below ground surface or deeper) and the borehole can be advanced relatively fast. It can be helpful when determining the top of the water table as the air begins to blow the water out of the borehole with the cuttings.

Cons: This can be problematic for contaminant investigations, as when foam needs to be added to recover the cuttings it introduces foreign materials. The collected samples are poor and more expertise is needed to interpret the cuttings. This method may not be suitable for some unconsolidated formations as there is minimal control of borehole caving if unconsolidated sands and silts are drilled.

2. Mud Rotary: Water or drilling mud circulated through the drill stem is used to bring the cuttings to the surface in the annular space between the borehole wall and the drill rod.

Pros: It can be used to make boreholes in which downhole geophysical logs can be run, can be drilled to great depth, and to get rock core samples. The borehole can also generally remain open after the drill stem has been removed.

Cons: The use of circulation fluids makes site clean-up more difficult than some other drilling methods. The drilling fluid can penetrate the formations changing the groundwater chemistry.

Sonic Methods: Uses high-frequency vibration (resonance) to reduce friction and advance the borehole. Drilling fluids (both liquid and air) can be used but are not required.

Pros: FAST – very fast drilling compared to other methods. It is useful in a wide range of soil types, including soils with large particles that are typically very difficult to sample using other techniques. It is used for numerous applications in the fields of environmental geology, engineering geology, and economic geology exploratory holes. With the sonic method, you can drill at any angle and it allows for the installation of well equipment, and the collection of relatively undisturbed soil samples and rock core.

Cons: Depending on conditions, it may be more expensive than conventional drilling methods. Friction from the drilling processes can create high temperatures for the drill bit, and this can be unwanted because it can volatilize the organic compounds being screened reducing accuracy. However, well-trained sonic drillers know how to mitigate the heat using several different techniques.

It’s not surprising that water well drilling is an ancient undertaking. About 8,000 years ago, the first water wells were hand dug to supply a safe, clean and reliable water source for the earliest civilizations. Our need for water has not changed, but well drilling technology has come a long way since then.

In some areas of the world, manually digging a water well is still the cheapest and most practical way to improve water accessibility, especially for one-off wells. However, for contractors and groups looking to add or expand their water well drilling capabilities long term, mechanical drilling can offer a faster, more efficient option.

There are two things to keep in mind when choosing water well drilling equipment: 1) The method must match the geology. 2) Consider the costs, both short term and long term. For a single well, manual techniques might not cost much, but can hand drilling methods handle soil conditions on your site? And how does the overall cost play out for digging multiple wells? On the other hand, mechanical well drilling options might be able to complete the job quickly but might not fit within the budget for an operation that is only looking at a few wells annually.

Let’s take a closer look at the pros and cons of some popular manual and mechanical drilling techniques to determine which might be the best option for your operation.

Manual Techniques

For many, digging a water well brings to mind an individual in a deep, muddy hole, passing up buckets of earth, and with good reason. Hand-digging is probably the oldest and most frequently used manual method for gaining access to ground water and it’s a labor-intensive, dirty job.

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Like other manual techniques – including sludging, manual percussion drilling, drive point and hand auguring – hand-digging requires only simple tools and a lot of hard work, which is why individuals and communities have been using these techniques effectively for so long. As the saying goes, “if it’s not broke, don’t fix it.” And for areas with limited access to heavy equipment or fuel, these techniques are still a viable option.

Pros:

• Requires simple tools that are locally accessible
• Can reach depths of 230 feet (70 meters) or deeper depending on method and geology
• Work can be completed quickly with large crews

Cons:

• High risk of surface contamination
• Difficult or impossible to drill through rock or dense soil
• Most methods become unstable at less than 33 feet (10 meters)
• Most methods require a high water table

Perhaps the biggest drawback to manually digging water wells is how inefficient the process is for multiple wells. Installing up to half a dozen wells in a single area might not break the bank, but repeatedly hiring large crews can add up quickly. Additionally, the geological impediments and the risk of contamination with manual techniques make them less attractive to contractors and groups looking to produce sustainable wells in multiple regions.

After considering the pros and cons, if manual drilling appears to be the best option for your project, manual percussion drilling is probably the most effective and widely used technique. The process consists of repeatedly dropping a heavy drill bit connected to a rope or cable in a hole partially filled with water to loosen soil and chip off pieces of rock. A sharpened drill bit and one-way valve at the bottom of the drill pipe can be added to create a hybrid percussion-sludging technique for increased efficiency. Manual percussion drilling is faster than other manual methods, capable of penetrating rock (very slowly) and is easily sealed to prevent contamination. However, mechanical percussion drilling — which mechanized the manual down-the-hole method — is a much more efficient option for operations looking for a long-term solution.

Mechanical Methods

Where manual drilling methods rely on simple tools, large work crews, hard work and patience to get the job done, mechanical drilling methods use motors, gears and fuel to power through rock and tough soils. These techniques can dig faster and deeper than manual methods and are ideal for contractors and groups looking for efficient, highly maneuverable easy-to-use equipment. For drilling a single well, they might not be cost efficient, but for operations looking to add water well drilling to their services, investing in the right water well drilling rig for your operation can offer fast ROI and open up new possibilities.

There are several popular methods, each with its own pros and cons, so consider your needs and the geology of your area of operation before committing to a mechanical drill rig.

Jetting: With this method, a pump forces water down a drill pipe and out a narrow nozzle to make a jet of water that loosens the sediment. Water outside the drill pipe carries cuttings up to the surface and into a settling pit, dug next to the borehole. The pump then returns the water back down the pipe. The drill pipe is suspended from a tripod and rotated by hand to keep the hole straight. In fine sand, this method can reach depths of 197 feet (60 meters).

Pros:

• Only requires two people
• Only tools are pump that can generate sufficient pressure and pipe

Cons:

• Only works in soft, fine-grained sediments
• Difficult to install sanitary seal to protect from surface contamination

Cable Tool: This is a mechanized version of manual percussion drilling. A heavy drill bit is attached to a steel cable and raised and dropped down the borehole. Cuttings are still manually removed with a bailer and several meters of water must be maintained in the borehole to keep the cuttings suspended. Equipment ranges from a basic skid-mounted winch with a tripod to a complex set of pulleys and drums with a large mast. Large cable tool rigs are mounted on a trailer or the bed of a truck and use hydraulic motors to raise and lower the mast and rotate the drums of the cable. These larger units are capable of drilling hundreds of feet deep through virtually any geological conditions.

Pros:

• Uses least amount of fuel

Cons:

• Slowest mechanical method
• Steel casing required to keep hole from collapsing when working in loose sediment
• Can require extra equipment like arc welder and cutting torch for drive casing

Mud Rotary: The basic concept behind the mud rotary drill rig is similar to jetting. Add a large cutting bit, lengths of steel drill pipe with threaded joints, a motor to turn and lift the drill pipe and a sturdy mast to support the pipe and you are ready for rotary well drilling. Mud rotary drilling also mixes bentonite clay or other materials in the jetting water to improve its ability to lift cuttings. This fluid is called “drilling mud” and is the “mud” referenced in the method’s name.

The two basic categories of mud rotary drilling are: table drive, where a rotating mechanism near the base of the rig turns the drill pipe, and top-head drive, where a motor attached to the upper end of the pipe turns it. In both cases, the upper end of the pipe is attached to a lifting mechanism that moves it along the mast. Both types of mud rotary rigs also have a swivel attached to the upper end of the pipe, allowing drilling mud to be pumped down the pipe while it is rotating.

Depending on size, a mud rotary rig can drill up to 3,281 feet (1,000 meters). The LS100 and LS200 drill rigs are mud rotary rigs at the small end of drill rig sizes, but even these smaller machines can drill an 8-inch (20-centimeter) borehole to a depth of 197 feet (60 meters). For more power in challenging soils, Lone Star developed the Hydraulic Series. The LS300H+ is capable of drilling a 6-inch (15-centimeter) borehole up to 300 feet (91.4 meters).

Pros:

• Drilling mud keeps borehole open eliminating need for drive casings
• Faster than cable tool and jetting methods

Cons:

• Drilling through rock only possible with larger rigs
• Multiple motors consume more fuel per hour than cable tool rig
• Large rigs require support vehicles to haul water and drill pipe

Air Rotary: The mechanical elements of an air rotary drill rig are similar to a mud rotary rig, including an option of table drive or top-head drive for rotating pipe. The principal difference is the use of compressed air to remove cuttings rather than drilling mud. The air rotary rig uses the same type of drill bits as the mud rig, but it can also drill with a down-the-hole hammer. It uses compressed air to break up rock and can drill very fast. A large air rotary rig can drill more than feet (500 meters) in the right geological conditions.

Pros:

• Fastest drilling method
• Quicker setup than other methods

Cons:

• Most expensive method
• Consumes the most fuel per hour
• Requires support vehicles and large air compressor

As you can see, there are lots of options for drilling water wells. The drilling method that works best for you, depends on your geology, your brawn and your budget.

Contact us to discuss your requirements of Water Well Drilling Rigs for Sale. Our experienced sales team can help you identify the options that best suit your needs.