Drilling 103: An Introduction to Air Rotary Casing Hammer (ARCH) Drilling

If you haven’t encountered air rotary casing hammer (ARCH) drilling before, you’re not alone. Although ARCH hasn’t received as much attention as methods like sonic drilling, it’s a solid option for drilling in alluvial formations that every environmental consultant should know.

What is ARCH Drilling and How Does It Work?

ARCH drilling combines direct air rotary drilling with the simultaneous operation of a casing hammer. An oversized casing is driven into an undersized bore using air as a circulation medium, allowing for efficient drilling and sampling.

When Should ARCH Be Used?

ARCH is best suited for alluvial formations and is not built to drill through hard rock. It can be used initially to cut through overburden and then be seated on bedrock, allowing drillers to switch to another method for bedrock drilling, such as direct air rotary with a downhole hammer or mud rotary.

ARCH is versatile and can be used for:

• Environmental monitoring wells

• Extraction and injection wells

• Soil vapor gas wells

• Mining projects

It is especially useful for projects requiring the separation of aquifers and running telescoping strings of drive casing.

Read about how we combined ARCH with other drilling methods on a project at Harney Basin. >>

Strengths of the ARCH Method

ARCH offers several key strengths:

1. No Secondary Waste Stream: As an air rotary drilling method, ARCH does not generate secondary waste streams like mud rotary drilling.

2. Efficient Surface Casing: ARCH allows setting a surface casing without permanent materials like steel and grout, saving time and money.

3. Instantaneous Cuttings Recovery: Air drilling in alluvial formations provides immediate cuttings recovery visible in the cyclone or containment vessel, making it easy to identify formations.

4. Controlled Well Construction: Like hollow stem auger or sonic drilling, the hole is cased, allowing for well construction in a controlled atmosphere and preventing borehole degradation.

5. Speed: ARCH is a fast method, capable of drilling 300 feet in four to six hours, often faster than sonic drilling.

Drawbacks of ARCH

The primary drawback of ARCH is its performance in aquifer-related drilling. Prolific aquifers can generate excessive water during air circulation, potentially necessitating a switch to a different drilling method.

Alternative Methods for Similar Lithologies

• Hollow Stem Auger: Suitable for shallower depths, conveying cuttings to the surface without a circulation medium.

• Sonic Drilling: Effective for deeper drilling where formations may not withstand air velocities or water erosion.

• Direct Air or Dual Tube Reverse: Options depending on formation stability.

Determining if ARCH is Right for Your Project

The best way to determine if ARCH is suitable for your project is to discuss it with a trusted and experienced drilling partner with no allegiance to any particular method. For example, during a recent project bid, we considered ARCH but ultimately chose sonic drilling for its cost-effective and expedient data collection in the required lithology.

In another case, our team installed 4” monitoring wells with slotted casings using ARCH, while another contractor used mud rotary for 8” extraction wells and 6” injection wells. The mud rotary method damaged borehole walls and aquifers, whereas ARCH provided significantly higher productivity.

ARCH is not the perfect solution for every drilling project, but in alluvial formations it is definitely one worth considering. If you’re interested in learning more about ARCH, Contact us using the form below or by visiting this link.