Comparison of Drilling Solutions for Different Formations: Equipment and Process Selection for Soft Soil, Gravel, and Rock Formations

Comparison of Drilling Solutions for Different Formations: Equipment and Process Selection for Soft Soil, Gravel, and Rock Formations

This is a concise guide on how to choose methods and equipment when drilling in different formations. We will use everyday language to help you understand the core concepts.

Core Principle: Tailored Approach

Drilling is like using different tools to dig different things. Digging sand, pebbles, and rock naturally require different methods and tools. The underground soil layer is what we need to "dig," and we must choose the appropriate solution based on its characteristics.

I. Soft Soil Formations (e.g., clay, sand)

Formation Characteristics: Like dough or wet sand, soft in texture and easily deformable, making drilling less strenuous, but the borehole wall is prone to collapse.

Core Challenge: Preventing borehole collapse and maintaining a smooth borehole wall.

Preferred Equipment: Rotary drilling rigs or long auger drilling rigs. They are like large "screwdrivers," quickly and cleanly "screwing" the soil out.

Processes and Techniques:

Fast Hole Formation: Equipment power does not need to be too high; focus on drilling speed.

Mud wall protection: A special "mud-water" (drilling fluid) is injected into the borehole, forming a thin protective film on the borehole wall, acting like "glue" to support the soil wall and prevent collapse.

Casing installation: If the soil layer is very loose, a temporary metal casing may need to be installed for support while drilling.

Summary: Fast, protective, and stable. Use a rotary drill to advance quickly and protect the drilled hole with mud or casing.

II. Gravel and pebble layers

Formation characteristics: Like a "bag of mixed stones" buried underground, with coarse, loose particles and large gaps. The drill bit is prone to getting stuck or being deviated from its course, and mud is also prone to leakage.

Core challenges: Dealing with loose formations and mud leakage, and maintaining the borehole direction.

Preferred equipment: Percussion drills or reverse circulation drills.

Percussion drills: Like a giant "pile hammer," the heavy hammer is lifted high and dropped repeatedly to crush the gravel, suitable for handling large-diameter pebbles.

Reverse circulation drilling: Its drill rod acts like a "giant vacuum cleaner," powerfully sucking out rock fragments from the center of the drill rod while drilling, resulting in high efficiency and thorough cleaning.

Techniques and Techniques:

Slow and Steady Progress: Don't rush; steadily break through gravel layers.

High-Viscosity Mud: Use exceptionally viscous mud to better coat the rock fragments and seal formation fissures, reducing loss.

Casing Drilling: Often, a "drilling while running casing" technique is necessary. A robust casing forcefully supports the loose rock layer; this is the most crucial step.

Summary: Break, Suction, Protect. Use impact force to break or powerfully suction out the rock fragments, and protect the borehole with casing throughout the process.

III. Hard Rock Formations (e.g., granite, limestone)

Formation Characteristics: Extremely hard and intact. Ordinary drill bits will only slip and barely penetrate.

Core Challenge: How to efficiently break hard rock.

Preferred Equipment: Roller cone drill bits, down-the-hole hammers, or rotary drilling rigs with rock-socketing drill bits.

Roller cone drill bits: These drill bits have several rolling "carbide teeth" that rely on immense pressure and rotation to crush and break the rock.

Down-the-hole hammers: These are "high-frequency rock drills" that inject high-pressure air into the bottom of the drill bit, generating thousands of impacts per minute. Combined with rotation, they "hammer" the rock, making them extremely efficient.

Process and Techniques: High pressure, low speed: In contrast to soft soil layers, immense downward pressure needs to be applied while reducing the rotation speed, allowing the drill bit sufficient force to break the rock.

Focusing on "hammering": The core principle is to break the rock structure through impact force (whether mechanical or pneumatic).

Air/water cooling: High temperatures are generated during drilling, requiring air or water to cool the drill bit and prevent wear or damage.

Summary: Pressure, hammering, breaking. Relying on heavy pressure and high-frequency impact to break rock, patience is key.