Which One Is More Suitable, Positive Circulation Drilling Rig Or Reverse Circulation Drilling Rig?

Drilling technology is important in geological exploration and resource development. Two important types of drilling rigs, positive circulation drilling rigs and reverse circulation drilling rigs, have their advantages due to their different working principles, mud circulation methods, drilling efficiency, and applications. The following will discuss the differences between positive circulation drilling rigs and reverse circulation drilling rigs from multiple angles to provide a basis for selection.

1. Working principle

Positive circulation drilling rig
The positive circulation drilling rig's working principle is based on the forward flow of mud. The drilling fluid is transported into the borehole by the mud pump, and the drill bit is cooled and carried with cuttings through the drill pipe and drill bit nozzle. The cuttings are then returned to the ground along the outer wall of the borehole. The whole process forms a closed forward cycle. This circulation method effectively cleans the drill bit and carries cuttings to the ground for processing.

Reverse circulation drilling rig
The principle of the reverse circulation drilling rig is opposite to the positive circulation, using air or hydraulic reverse flow. The drilling fluid is pumped from the ground into the bottom of the well through the center hole of the drill pipe, and the cuttings are sucked to the ground through the center hole of the drill pipe by negative pressure or gas lift. Since the cuttings are discharged directly from the inside of the drill pipe, the reverse circulation has a higher cutting removal efficiency and avoids the accumulation of cuttings in the well.

2. Drilling efficiency

Due to the difference in cutting removal path and efficiency, the reverse circulation drilling rig is superior to the positive circulation drilling rig in drilling efficiency.

Efficiency characteristics of positive circulation drilling rig

• It is suitable for soft rock and soil layers, and the drilling speed is moderate.
• The cuttings return to the ground along the well wall, and the path is long, which may cause the mud viscosity to increase and affect the cutting removal efficiency.

Efficiency characteristics of reverse circulation drilling rig

• The cuttings are discharged through the inner hole of the drill pipe, with a short path and high efficiency.
• It performs well in hard rock and complex formations and can significantly increase the drilling speed.

3. Application

Application of positive circulation drilling rig

• Geological conditions such as soil layers and soft rock formations.
• Wells with a drilling depth (500-1500 meters), such as farmland irrigation wells and geological exploration wells.
• Cost-sensitive projects, due to the simple positive circulation system, the operating cost is low.

Application of reverse circulation drilling rigs

• Hard rock and complex geological conditions, such as drilling of deep wells and high-hardness rock formations.
• Projects with high requirements for drilling quality, such as mining and geothermal well development.
• For Projects with high environmental protection requirements, the reverse circulation system can better control drilling fluid leakage and wellbore stability.

4. Advantages and Disadvantages

Advantages and Disadvantages of Positive Circulation Drilling Rigs

Advantages:

The system is simple and easy to operate and maintain.

The mud circulation cost is low, and suitable for projects with limited budgets.

The disturbance to the formation is small, which is conducive to the stability of the wellbore.

Disadvantages:

The chip removal efficiency is low, which affects the drilling speed.

In complex formations, the mud circulation may be hindered, reducing work efficiency.

Advantages and Disadvantages of Reverse Circulation Drilling Rig

Advantages:

High chip removal efficiency and fast drilling speed.

It can effectively avoid the accumulation of rock chips and improve the quality of drilling.

It performs well in complex formations and deep well drilling.

Disadvantages:

The system is complex, and the equipment cost and operating cost are high.

It requires professional technicians to operate, which increases the labor cost.

5. How to choose

When choosing a positive circulation drilling rig or a reverse circulation drilling rig, the following factors need to be considered:

Positive circulation drilling rigs are suitable for projects with limited budgets and low operating costs:

• If the formation is stable and the drilling depth is shallow, a positive circulation drilling rig is preferred.
• If the formation is complex or the hardness is high, a reverse circulation drilling rig should be selected to improve efficiency and quality.

Reverse circulation drilling rigs are suitable for high-demand projects. Although the cost is higher, the efficiency and effect are better:

• For projects with high environmental protection requirements, such as urban construction or environmentally sensitive areas, reverse circulation drilling rigs can be selected.
• For ordinary water wells and shallow geological exploration, positive circulation drilling rigs are sufficient.
• For high-difficulty projects such as deep wells, mines or geothermal wells, reverse circulation drilling rigs are a better choice.

6. Conclusion

As two important equipment in drilling operations, positive circulation drilling rigs and reverse circulation drilling rigs have obvious characteristics and advantages. Positive circulation drilling rigs are suitable for shallow and soft formations with their simple and economic characteristics, while reverse circulation drilling rigs have advantages in deep wells and complex formations with their efficient chip removal capabilities and strong adaptability. We should conduct a comprehensive evaluation based on the specific needs, geological conditions, and budget of the project to achieve the best drilling effect and economic benefits.