Cable Tool Drilling

What Is Cable Tool Drilling?

Cable tool drilling is a percussion-based method used to construct water wells.

It is also commonly known as:

• Percussion drilling
• Spudder drilling
• Cable tool well drilling

Unlike rotary drilling, which continuously rotates a drill bit, cable tool drilling repeatedly lifts and drops a heavy drill string into the borehole.

Each impact breaks, crushes, or loosens the subsurface material.

Water is often added to the borehole to mix with the loosened material and create a slurry. The slurry is then removed using a bailer or sand pump.

This process is repeated until the desired depth or water-bearing formation is reached.

Cable tool drilling can be used in:

• Hard rock
• Fractured rock
• Sand
• Gravel
• Cobbles
• Boulder formations
• Mixed geological conditions
• Unstable formations

The suitability of the method depends on the expected geology, well depth, casing requirements, equipment available, site access, and the professional judgment of the drilling contractor.

Important: Cable tool drilling constructs the borehole. It does not independently locate groundwater or guarantee a specific well yield.

How Cable Tool Drilling Works

Cable tool drilling relies on repeated percussion rather than continuous rotary cutting.

A heavy drilling assembly is suspended from a cable and repeatedly raised and dropped inside the borehole.

Each impact breaks or loosens material at the bottom of the hole.

A typical drilling process may include the following steps:

1. The drilling rig is positioned over the proposed well location.
2. The drill string is lowered into the borehole.
3. The rig repeatedly lifts and drops the drilling tools.
4. The drill bit breaks or loosens the formation.
5. Water may be added to help create a slurry.
6. The drill string is periodically removed.
7. A bailer or sand pump removes the loosened material.
8. Casing may be advanced as drilling progresses.
9. The drilling process continues until the required depth is reached.
10. The completed well is developed and tested.

The Cable Tool Drill String

A traditional cable tool drill string usually includes several main components.

These include:

• Drill bit
• Drill stem
• Drilling jars
• Swivel socket
• Drill line

Each component has an important role in the drilling process.

The Cable Tool Drill String

The drill bit is located at the bottom of the drill string.

It repeatedly strikes the subsurface formation and breaks or loosens the material.

Different bit designs may be used depending on the formation, including:

• Hard rock
• Soft rock
• Gravel
• Clay
• Sand
• Mixed formations

The condition and design of the drill bit can significantly affect drilling efficiency.

Drill System

The drill stem adds weight to the drill string.

The additional weight increases the force of each impact against the formation.

The appropriate drill-stem weight depends on the equipment, borehole diameter, formation type, and drilling conditions.

Drilling Jars

Drilling jars provide controlled movement within the drill string.

They can help the operator free drilling tools when they become stuck or tightly lodged in the borehole.

Jars are especially useful in difficult drilling conditions.

Swivel Socket

The swivel socket connects the drill line to the drill string.

It allows slight rotation during drilling and can help reduce cable twisting while promoting more even tool wear.

Drill Line

The drill line supports the drill string and transfers the lifting motion from the rig to the drilling tools.

Because the cable repeatedly carries substantial weight, it must be properly inspected and maintained.

Removing Cuttings With a Bailer

Unlike air rotary or mud rotary drilling, cable tool drilling does not continuously carry cuttings to the surface.

Instead, the drilling tools are periodically removed from the borehole.

A bailer or sand pump is then lowered into the hole.

The bailer collects the slurry made up of:

• Water
• Crushed rock
• Sand
• Gravel
• Clay
• Other loosened material

The bailer is then raised to the surface and emptied.

This process may be repeated several times before drilling continues.

Removing the cuttings helps keep the bottom of the borehole clean and allows the drill bit to continue working efficiently.

Unlike air rotary or mud rotary drilling, cable tool drilling does not continuously carry cuttings to the surface.

Instead, the drilling tools are periodically removed from the borehole.

A bailer or sand pump is then lowered into the hole.

Cable Tool Drilling in Consolidated Rock

Cable tool drilling can be used in consolidated formations such as:

• Limestone
• Sandstone
• Shale
• Granite
• Basalt
• Other competent rock formations

In hard rock, the drill bit repeatedly strikes the bottom of the borehole.

The repeated impacts crush and break the rock into smaller fragments.

Water may be added to create a slurry so the cuttings can be removed with a bailer.

Several factors can affect drilling speed, including:

• Rock hardness
• Rock fractures
• Drill bit condition
• Drill-string weight
• Stroke length
• Impact frequency
• Borehole diameter
• Amount of cuttings remaining at the bottom of the hole

Cable tool drilling in solid rock is usually slower than many modern rotary drilling methods.

However, the method can allow the operator to closely observe formation changes and groundwater entering the borehole.

Cable Tool Drilling in Sand, Gravel and Unconsolidated Formations

Cable tool drilling can also be used in loose or unconsolidated formations.

Examples include:

• Sand
• Gravel
• Cobbles
• Glacial deposits
• Loose sediments
• Boulder formations

In these conditions, the borehole may collapse if it is left unsupported.

For this reason, casing is often advanced as drilling progresses.

The casing helps:

• Support the borehole
• Prevent loose material from collapsing inward
• Protect completed sections of the borehole
• Isolate unstable formations
• Allow drilling to continue safely

The drill bit generally works slightly ahead of the casing.

As material is removed, the casing is gradually advanced deeper into the ground.

In difficult formations, smaller casing may sometimes need to be installed inside larger casing. This is commonly referred to as telescoping casing.

The drilling contractor should determine the appropriate casing procedure based on the actual geological conditions encountered.

When Is Cable Tool Drilling a Good Choice?

Cable tool drilling may be considered in certain geological and site conditions.

It may be useful when:

• The formation contains gravel, cobbles, or boulders.
• Loose material makes borehole stability difficult.
• Lost circulation creates problems for rotary drilling.
• Thin water-bearing zones need to be observed carefully.
• Large amounts of drilling fluid are undesirable.
• Casing must follow closely behind the drill bit.
• The geology contains fractured or broken rock.
• The formation contains cavities or highly disturbed zones.
• Access is limited for larger drilling equipment.
• The contractor has suitable cable tool equipment and experience.

Cable tool drilling is not automatically the best option for every water-well project.

The final drilling method should be selected by a qualified or properly licensed drilling contractor after considering:

• Expected geology
• Required well depth
• Water demand
• Borehole diameter
• Casing requirements
• Equipment availability
• Site access
• Local regulations

Advantages of Cable Tool Drilling

Limitations of Cable Tool Drilling

Cable Tool Drilling vs. Rotary Drilling

Different drilling methods are suited to different geological conditions.

Factor	Cable Tool Drilling	Air Rotary Drilling	Mud Rotary Drilling
Basic drilling action	Repeated percussion	Rotating bit with compressed air	Rotating bit with drilling fluid
Typical speed	Usually slower	Often faster in hard rock	Often efficient in loose formations
Cuttings removal	Bailer or sand pump	Compressed air	Circulating drilling fluid
Hard rock	Suitable	Very suitable	Suitable in some conditions
Loose formations	Can be effective with casing	May require casing	Often suitable
Borehole support	Casing often follows drilling	May require casing	Drilling mud helps support the borehole
Fluid requirements	Relatively low	Usually limited	Usually higher
Formation observation	Very good	Good	May be more difficult
Equipment footprint	Often smaller	Usually larger	Usually larger
Common use	Mixed or difficult formations	Competent hard rock	Loose or unstable formations

No single drilling method is best for every water-well project. The drilling contractor should select the method based on the actual formation, site conditions, equipment, and project requirements.

 Cable Tool Drilling vs. Air Rotary Drilling

Air rotary drilling uses compressed air to continuously carry cuttings out of the borehole.

Cable tool drilling removes cuttings periodically using a bailer.

Air rotary drilling can be significantly faster in competent hard rock.

Cable tool drilling may be useful where:

• Loose formations are present
• Large boulders are encountered
• Borehole stability is difficult
• Lost circulation is a concern
• Casing needs to follow closely behind drilling

Learn more about air rotary drilling for water wells.

Cable Tool Drilling vs. Mud Rotary Drilling

Mud rotary drilling circulates drilling fluid through the borehole.

The drilling fluid helps:

• Carry cuttings to the surface
• Support unstable formations
• Cool the drill bit
• Maintain borehole stability

Cable tool drilling generally requires less circulating fluid.

This may be useful where drilling-fluid management is difficult.

Mud rotary drilling is often faster in deep unconsolidated formations.

The most appropriate method depends on the actual geology and well design.

Why Evaluate Groundwater Before Drilling?

Cable tool drilling determines how the borehole is constructed. IIt does not determine where the most promising groundwater target is located. Groundwater conditions can vary considerably across a property.

Two wells located relatively close to each other may encounter different:

• Well depths
• Rock formations
• Water-bearing fractures
• Aquifer thicknesses
• Water yields
• Water quality

Before drilling, property owners may benefit from reviewing as much information as possible.

A pre-drilling evaluation may include:

• Reviewing nearby water-well records
• Studying available geological information
• Evaluating property access
• Comparing possible drilling locations
• Completing a groundwater survey
• Estimating possible water-bearing zones
• Discussing the results with the drilling contractor

WaterFind USA uses advanced seismic methods and available well information to help evaluate potential groundwater conditions before drilling. Survey findings are estimates. Actual groundwater conditions can only be confirmed through:

• Drilling
• Well development
• Pump testing
• Water-quality testing

WaterFind USA helps property owners evaluate potential groundwater conditions before drilling. The purpose of the survey is not to replace the drilling contractor.

Instead, the survey provides additional information that can support the planning process.

WaterFind USA can assist with:

• Groundwater site assessment
• Pre-drilling groundwater surveys
• Review of available water-well records
• Potential drilling-location comparison
• Estimated water-bearing zone evaluation
• Seasonal project scheduling
• Water-well planning information

Survey information can be shared with the contractor responsible for constructing the well.

The contractor can then consider:

• Groundwater survey results
• Nearby well records
• Site geology
• Required well depth
• Access conditions
• Drilling equipment
• Casing requirements
• Local regulations
• Intended water use

The final drilling method and well design should always be determined by the qualified contractor responsible for constructing the well.

WaterFind USA Service Area

WaterFind USA currently schedules seasonal service routes in selected western and central U.S. states.

Related Water-Well Planning Resources

• Learn how air rotary drilling works in hard-rock formations.
• Compare direct rotary drilling methods.
• Review factors that affect water-well drilling costs.
• Review groundwater survey pricing and seasonal service areas.
• Check available water-well records before selecting a drilling location.
• Learn how groundwater surveys can support pre-drilling decisions.