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XinHao Drilling Rig：Why Rock Core Sampling Fails in Field Drilling Projects

In geological exploration, Rock Core Sampling quality directly determines the accuracy of exploration data.
However, many contractors face common problems such as broken cores, low recovery rates, sand-filled core barrels, or even empty core tubes.

Based on years of field service experience, XinHao Drilling Rig has found that over 80% of incomplete core recovery issues are caused by improper drilling mud ratios and insufficient hole cleaning, rather than the drilling machine itself.

This guide explains practical, field-proven solutions to help you improve core recovery using the right mud mix and cleaning methods—especially when working with a rock core drilling machine or crawler rig in remote locations.

1. Match Drilling Mud to Geological Conditions (No One-Size-Fits-All)

In field operations, professional mud testing tools are rarely available.
Instead, operators should rely on visual observation and hand-feel judgment.

The key principle is simple:

Hard rock → prevent core abrasion
Soft rock → prevent mud adhesion
Fractured formations → prevent hole collapse

1.1 Hard Rock Formations (Granite, Basalt)

Common issues

Core surface abrasion
Core breakage caused by excessive flushing force

Recommended mud ratio

Bentonite: 5–8%
Clean water: 92–95%
Soda ash: 0.3–0.5%

Field judgment

Smooth, lump-free mud
Stable return flow at the hole mouth
Clean core surface without scratches

Operational tips

Mix for 8–10 minutes before drilling
Maintain low circulation flow (30–50 L/min)
Reduce impact on the core while ensuring cooling

1.2 Soft Rock or Clay Formations (Shale, Mudstone)

Common issues

Core disintegration
Mud sticking to the inner core barrel

Recommended mud ratio

Bentonite: 3–5%
Clean water: 95–97%
Thinner (e.g., lignosulfonate): 0.2%

Field judgment

Thin slurry consistency
Spreads quickly on the ground (10–15 cm diameter)
No mud adhesion inside the core tube

Operational tips

Higher circulation rate (60–80 L/min)
Use thinner to reduce stickiness
Emergency alternative: laundry detergent (small dosage)

1.3 Fractured or Weathered Rock Formations

Common issues

Hole collapse
Crushed or blocky core samples

Recommended mud ratio

Bentonite: 10–12%
Clean water: 88–90%
Soda ash: 0.5–0.8%
CMC: 0.3%

Field judgment

High viscosity
Forms thin strings (3–5 cm) on the mixing rod
Stable mud return without large debris

Operational tips

Never interrupt circulation
Add materials in sequence to avoid clumping
Essential for deep-hole rock core drilling machine operations

2. Scientific Hole Cleaning: 3 Key Steps to Improve Core Recovery

Effective hole cleaning is as important as drilling itself—especially for crawler rig operations in deep or unstable formations.

2.1 Clean While Drilling

Every 2–3 meters, stop feed pressure
Keep rotating and circulate mud for 5–8 minutes
Prevent cuttings from settling at the hole bottom

Tip:
If return flow slows or debris increases, extend cleaning time to 10 minutes.

2.2 Intensive Cleaning Before Core Sampling

Raise the drill rod 50 cm
Increase circulation flow by 30%
Clean for 10–15 minutes

Quality check

Clear mud return
After 5 minutes of standing, sediment ≤ 2 mm

2.3 Secondary Cleaning After Core Retrieval

Used mainly in soft or sandy formations.

Use thinner mud (30% lower viscosity)
Circulate for 3–5 minutes
Pressure ≤ 1.5 MPa to protect hole walls

3. Supporting Operations That Protect Core Integrity

3.1 Optimize Drilling Parameters

Formation TypeFormation Type	Rotation Speed	Weight on Bit
Hard rock	80–100 rpm	5–8 kN
Soft rock	50–70 rpm	3–5 kN
Fractured rock	60–80 rpm	4–6 kN

3.2 Proper Core Barrel Handling

Hoisting speed ≤ 0.3 m/min
Avoid sudden lifting
Tap the barrel side gently with a rubber hammer
Wrap soft cores immediately to prevent drying cracks

3.3 Maintain Mud Circulation System

Clean pump filters daily
Use lined mud pits to avoid contamination
Reverse air flushing for blocked pipelines (≤ 2 MPa)

4. Common Mistakes in Rock Core Sampling

❌ “Thicker mud is always better”
❌ “Longer hole cleaning improves results”
❌ “Poor cores mean bad drill bits”
❌ “Mud can be reused indefinitely”

In reality, mud contamination and poor cleaning are the main causes of low recovery, even when using high-quality equipment from professional core drilling rig manufacturers.

5. Emergency Solutions for Field Drilling

Sudden hole collapse: switch to high-viscosity mud immediately
Circulation failure: lift rods slowly and re-clean before drilling
Core stuck in barrel: use small amounts of diesel for lubrication (never heat)

Conclusion: Stable Core Recovery Is a Process, Not Luck

Reliable Rock Core Sampling depends on two fundamentals:

1.Formation-matched drilling mud

2.Thorough, controlled hole cleaning

With correct procedures, core recovery rates can consistently exceed 95%, even in complex geological conditions.

XinHao Drilling Rig integrates optimized mud circulation systems and anti-adhesion core barrels into every rock core drilling machine, helping both new and experienced operators achieve stable results in the field.

If you are looking for reliable solutions from experienced core drilling rig manufacturers, XinHao offers equipment and technical support designed specifically for real-world exploration challenges.

3 Core Sampling Tips to Prevent Breakage & Loss for Geological Core Drill Rigs