Borehole Development Methods: Surge, Air Lift, and Jetting

What is Borehole Development?

Borehole development is the critical process of cleaning a newly drilled borehole to remove drilling fluids, cuttings, and fine particles that have accumulated around the screen and in the surrounding formation. This process transforms a "drilled hole" into a functional water well by opening up the aquifer to allow water to flow freely into the borehole.

At WaterLink Limited, a WRA licensed borehole drilling company with Class A status, we use professional development methods on every borehole we drill. This guide explains the three main borehole development methods—surge block, air lift, and jetting—and why proper development is essential for maximizing yield and ensuring long-term performance.

Why Borehole Development is Critical

During drilling, the borehole is filled with drilling fluids (mud) to stabilize the hole and carry cuttings to the surface. This drilling mud invades the formation and coats the screen, blocking water flow. Here's why development is essential:

• Removes Drilling Mud: Drilling fluids left in the formation will permanently reduce water flow.
• Cleans Screen Openings: The borehole screen must be completely clean for water to enter.
• Opens Aquifer Channels: Development helps create flow paths from the aquifer to the borehole.
• Removes Fine Particles: Sand, silt, and clay particles that can block the screen are flushed out.
• Maximizes Yield: Proper development ensures the borehole achieves its full potential.
• Prevents Premature Failure: A poorly developed borehole may fail within months.
• Ensures Long-Term Performance: Well-developed boreholes perform consistently for decades.

The Three Main Development Methods

WaterLink Limited uses three proven development methods, often in combination:

Surge Block Development

The surge block (also called a surge plunger) is a tool with rubber flanges that fits tightly inside the casing. It's moved up and down rapidly within the screened interval, creating alternating positive and negative pressure surges.

How It Works

• Downward stroke: Creates positive pressure that forces water and particles outward through the screen
• Upward stroke: Creates negative pressure that pulls water and particles inward through the screen
• Continuous surging: This back-and-forth action breaks up mud cakes and flushes particles from the formation

Advantages

• Highly effective for screen cleaning
• Does not require compressed air equipment
• Can be used in deep boreholes
• Relatively gentle on the formation

Limitations

• Less effective for removing drilling mud from the formation
• Requires access to the borehole (pump removed)
• Can be time-consuming for deep boreholes

Air Lift Development

The air lift method uses compressed air injected at the bottom of the borehole. The air mixes with water, reducing its density and creating an upward flow that carries drilling mud, debris, and fine particles out of the borehole.

How It Works

• Compressed air is injected through an air line to the bottom of the borehole
• Air bubbles mix with water, creating a low-density column
• The pressure difference between the column and the surrounding water creates upward flow
• Water, mud, and debris are lifted to the surface at high velocity

Advantages

• Excellent for removing drilling mud and large debris
• Can handle high sediment loads
• Effective for developing the formation
• Can be used to pump water for test pumping

Limitations

• Requires compressed air equipment (air compressor)
• Less effective for fine screen cleaning
• Can cause turbulence that damages sensitive formations

Jetting Development

Jetting uses high-pressure water jets directed at the screen to dislodge particles and clean the screen openings. The jetting tool is moved up and down through the screen interval while high-pressure water is directed outward through the screen.

How It Works

• A jetting tool with high-pressure nozzles is lowered into the borehole
• Water is pumped at high pressure (100-300 psi) through the nozzles
• The jets are directed at the screen openings to flush out particles
• Dislodged particles are carried to the surface by the return flow

Advantages

• Highly effective for cleaning screen openings
• Can be combined with surging for maximum effect
• Good for removing fine particles

Limitations

• Requires high-pressure pumping equipment
• Less effective for removing drilling mud from the formation
• Not suitable for all formation types

Method Comparison

Here's a quick comparison of the three development methods:

Note: WaterLink Limited often combines all three methods for optimal results.

The Development Process

Here's how WaterLink Limited develops a borehole:

Development Costs in Kenya

The cost of borehole development depends on the depth, method, and time required:

Note: Costs vary based on borehole depth, accessibility, and specific conditions.

What Happens If Development is Skipped?

Some contractors skip development to save time and money. Here's what happens when development is inadequate:

• Reduced Yield: Flow rates can be 30-50% lower than potential.
• Sediment in Water: Fine particles continue to enter the borehole, causing cloudy water.
• Premature Pump Failure: Sediment damages pump impellers.
• Screen Clogging: Over time, particles pack against the screen, further reducing flow.
• Borehole Failure: In severe cases, the borehole may stop producing water entirely.
• Higher Electricity Costs: The pump works harder to produce less water.

How WaterLink Limited Develops Boreholes

WaterLink Limited uses professional development methods on every borehole we drill:

• Combined Approach: We use all three methods—air lift, surge block, and jetting—for optimal results.
• Professional Equipment: We use professional surge blocks, air compressors, and high-pressure pumps.
• Experienced Technicians: Our technicians are trained in all development methods.
• Clear Water Standard: We develop until the water runs completely clear.
• Documentation: We document the development process and include it in our project report.