Suggestions for selecting well drilling rigs under different geological conditions

Suggestions for selecting well drilling rigs under different geological conditions

Choosing the right drilling rig for different geological conditions is the key to ensuring drilling efficiency, cost control and well quality. The following is a reference for model selection for several common strata.

1. Soft soil layer (such as clay, silt, farmland soil)

Geological characteristics: soft texture, small resistance, but prone to collapse.

Preferred model: auger drill (commonly known as "earth drill").

Reasons and key points: The auger drill uses the rotation of the blades on the drill pipe to directly cut the soil layer and continuously bring the soil out of the ground. It is extremely efficient and can form holes quickly. It is very suitable for shallow wells with a depth of less than 30 meters. Simple operation and convenient transfer. The key is to maintain a reasonable rotation speed to prevent the soil on the blades from being squeezed too much and making it difficult to discharge.

2. Sand layer, gravel layer and loose pebble layer

Geological characteristics: loose structure, poor stability, prone to hole collapse and slurry leakage, and high requirements for wall protection.

Preferred model: light rotary drilling rig (equipped with mud circulation system).

Reasons and key points: This model breaks the formation by rotating the drill bit, and at the same time uses a mud pump to continuously transport mud (bentonite and water mixture) into the hole. Mud can play the core role of cooling the drill bit, carrying drilling debris, and forming a protective film on the well wall to stabilize the hole wall. This is an effective way to deal with such unstable formations. Care needs to be taken to control mud consistency.

3. Hard rock layers (such as granite, limestone)

Geological characteristics: extremely high hardness, ordinary rotary cutting is ineffective.

Preferred models: pneumatic or hydraulic down-the-hole hammer drills, or heavy-duty rotary drills (equipped with cone drill bits or diamond drill bits).

Reasons and key points: The down-the-hole hammer drilling rig uses high-pressure air to drive the hole bottom impactor to generate high-frequency impact force to break the rock. The efficiency is much higher than that of simple rotation. Heavy-duty rotary drilling rigs rely on high torque and special hard drill bits to grind rocks. The price and energy consumption of these two models are relatively high, and they need to be selected based on the rock hardness and budget.

4. Complex mixed strata (such as soil layers, sand layers, and rocks appearing alternately)

Geological characteristics: The same well will pass through a variety of strata with different properties, requiring the drilling rig to be highly adaptable.

Preferred model: multi-functional compound drilling rig (such as a model that combines a pneumatic down-the-hole hammer with a rotary drill).

Reasons and key points: This type of drilling rig can cope with different formations by changing drilling tools and working modes. For example, the spiral or rotary mud method is used for the upper soft layer, and when the hard rock layer is encountered, it is switched to the down-the-hole hammer impact mode. One machine has multiple functions and is highly flexible. It is an ideal choice for dealing with complex geology, but the operational technical requirements are also higher.

Summary suggestions: Geological survey first, give priority to adaptability

The fundamental of type selection is to understand the geological conditions of the target well location in advance as much as possible. You can refer to the drilling records of existing water wells in the surrounding area, or conduct a simple survey.

General principle: If the formation is single, it is most efficient to select a targeted professional model; if the formation is complex and changeable, priority should be given to models with certain multi-functional adaptability to avoid the machine being completely unable to work when encountering unexpected hard layers.

Consult local experts: The most direct and effective method is to consult with local experienced well drilling teams or dealers. They know best which type of local machine is “most successful”.

The correct selection can not only get twice the result with half the effort, but also avoid drilling failures and economic losses caused by insufficient machine capabilities.