What Is The Best Casing Pipe for Drilling in Soil?

‌The best casing pipe type for drilling in soil depends on the depth and geological conditions of the well. Different depths and geological conditions have different performance requirements for casing pipe, so it is crucial to choose casing pipe reasonably.

The best casing pipe type for different depths and geological conditions

1. Shallow hole drilling (less than 1000 meters)

Plastic fiber pipes (such as PVC pipes), cast iron pipes and straight seam welded pipes are often used. They are low-cost and easy to install, suitable for ordinary shallow water wells and agricultural irrigation wells. However, due to limited strength, it is difficult to effectively protect the wall under complex geological conditions.

2. Medium-depth drilling (1000-2000 meters)

Low-grade seamless steel pipe is a better choice, such as 20#-40# steel grades. It has good strength and toughness, can withstand certain pressure and stress changes, and is suitable for medium-depth wells under ordinary geological conditions.

3. Deep hole drilling (more than 2000 meters)

High-grade seamless steel pipes are required, such as DZ40 and above. As the depth increases, the formation environment becomes complex. High-grade seamless steel pipes have high strength, good toughness, and fatigue resistance, which can ensure the safety and stability of ultra-deep wells, such as ultra-deep oil exploration wells.

Main points of casing pipe materials and performance

1. Plastic fiber pipe, cast iron pipe, straight seam welded pipe

These pipes have low strength, poor mechanical properties of plastic fiber pipe, large brittleness of cast iron pipe, and weak welds of straight seam welded pipe. They are mainly used for shallow holes and water wells, and are not suitable for drilling with high wall protection requirements.

2. Spiral welded pipe

Suitable for wall casing pipe shallower than 1000 meters. It is made by spiral welding and has a certain strength, but the overall performance is inferior to seamless steel pipes. It is usually necessary to reinforce the periphery with cement to enhance stability.

3. Seamless steel pipe

According to the steel grade, it is divided into J55, K55, N80, etc., and the performance of different steel grades is different. It must comply with API pipe standards, with strict specifications for chemical composition, mechanical properties, etc., and the thread processing must meet the requirements to ensure a tight connection and ensure the safety of the drilling system in harsh environments.

Methods of lowering casing pipe

1. Lowering the first section of casing pipe

Place the bottom of the first section of casing pipe on the wellhead device, slowly lift the casing pipe through the lifting equipment, make the casing pipe perpendicular to the wellhead, and then slowly lower it into the wellbore. During this process, someone should observe the lowering of the casing pipe near the wellhead to ensure that the casing pipe descends vertically to avoid colliding with the well wall.

2. Subsequent casing pipe connection and lowering

After the first section of casing pipe is lowered to a certain depth (usually most of the casing pipe length), lift the second section of casing pipe and connect it to the first section of casing pipe. If it is a threaded connection, apply an appropriate amount of thread sealing grease on the thread, then rotate the casing pipe to make the thread tightly bite; if it is a welded connection, operate in accordance with the welding process specifications to ensure the welding quality. After the connection is completed, continue to lower the casing pipe, and repeat this process until the designed casing pipe lowering depth is reached.

3. Straightening and centering

In the process of lowering each section or every few sections of casing pipe, a stabilizer should be installed. The stabilizer is usually installed on the outer wall of the casing pipe. Its function is to keep the casing pipe in the center position in the wellbore, reduce the friction between the casing pipe and the wellbore wall, and make the cement around the casing pipe (if cementing is required) more evenly distributed.

Summary

Choosing the right casing pipe is the key to ensuring the safety and efficiency of soil drilling. In actual operation, the drilling depth, geological conditions and casing pipe characteristics should be comprehensively considered and reasonably selected. It is expected that with the development of technology in the future, more high-quality casing pipe will help the drilling industry reach new heights.