How to Deal with the Slipping of Rotary Drilling Rigs When Drilling into Mudstone or Silt Layers!

When drilling into mudstone or silt layers, rotary drilling rigs often slip, that is, the drilling rig pressurization action is ineffective, and drilling is impossible or difficult, thus affecting the construction progress and production efficiency. The following is an introduction to effective methods for rotary drilling rigs in mudstone drilling.

1. Overview of Mudstone

Mudstone, sandy mudstone, muddy sandstone, sandstone, and shale are sedimentary rocks that are red, dark re,d or brown because they contain rich oxides. These rocks are collectively called red sandstone. Red sandstone mainly presents two typical structural forms: granular clastic structure and muddy cemented structure. Most red sandstones can be disintegrated and broken, or even muddied, under the influence of the atmospheric environment, so the size and particle size of the rock blocks will change over the time course of the dry-wet cycle. Mudstone is a sedimentary rock solidified by mud and clay. Its composition and structure are similar to shale but it is less fragile. A clay rock with unclear bedding or foliation. Mudstone has water absorption and bonding properties. The photo below shows a typical mudstone layer.

2. Causes of Slip

During the construction process, if a dry hole is drilled into mudstone, the drilling efficiency is higher when using a spiral drill bucket. If a double-bottom sand bucket is used, drilling can also be carried out, but the load is larger. Once the hole encounters water, slippage will occur immediately. Therefore, slippage is directly related to water or mud. Therefore, the main reasons for mudstone slippage are composed of the following: 1. The hardness of mudstone; 2. The lubrication effect of water or mud; 3. The softening of mudstone by water absorption, etc.

3. Drilling with Different Drilling Tools

1. When the spiral drill bucket drills into the mudstone of the water hole, the mudstone softens when it meets water, and the cone head at the front end of the spiral drill bucket will be filled with mudstone debris to form a whole. The drill tool loses its drilling function and cannot continue to drill. Water or mud enters between the drill bucket and the mudstone to lubricate, resulting in slippage.

2. When using a double-bottom pick drill bucket to drill into the mudstone water hole, the pick drilling method is to use the front alloy head to drill. The alloy head can easily break into the mudstone, but because the front alloy head is very short, the pick body that fixes the alloy head must follow up and cut in. Because the pick body is too blunt, resistance is formed, causing the pick to break into the mudstone too shallowly. The mudstone is cemented, so the crushing effect cannot be achieved. In addition, a large amount of silt will adhere to the outer cylinder wall of the drill bucket during the drilling process, causing "floating drill". Therefore, it cannot continue to drill, resulting in slippage.

3. Through the above analysis, mudstone has good cementation and is not easy to break. It requires sharper tools, deeper drilling and smaller cutting resistance to achieve the effect of cutting and breaking.

4. Solutions for Slipping During Mudstone Drilling:

Therefore, the double-bottom sand bucket and cutting drilling are in line with the above analysis. However, the actual sand bucket will also slip, but there are many factors involved.

1. Defects on the drill bucket, such as the center positioning tip is not too long, too wide, or too blunt, the angle of the tooth tip and the gap between the tooth seat, the diameter of the side teeth, the model of the bucket teeth or the wear of the tooth tip. It is best to improve the height difference of the tooth tip length and reduce the contact area. The drill bucket in the figure below is specially improved for drilling mudstone, including reverse installation of bucket teeth and lengthening of bucket teeth.

2. The diameter of the sand bucket. The larger the diameter of the drill bucket, the larger the contact area, and the more difficult it is to overcome slippage. Therefore, for piles with larger diameters, a drill bucket with a smaller diameter can be used for drilling.

3. Analysis of overcoming slippage As mentioned earlier, the main reason for slippage is caused by water or mud lubrication. Therefore, as long as the softened mudstone and the water or mud on the surface are overcome, mudstone slippage can be overcome! After overcoming it, continue to pressurize the drilling, and try to reduce the idling of the power head in the hole. Water or mud cannot enter the cutting surface, so that the tooth tip is always in contact with dry geology, and normal drilling can be carried out.

4. Operational control is very important. Since mudstone is hard and has good cementation, it is not easy to cut in under water lubrication. First, lift the power head to the highest position, then control the power head to rotate slowly, and pressurize slowly and continuously. The power head and pressurization speed must be well-matched. If the pressurization stroke is completed and the mudstone is not cut in, lift the power head again to continue drilling until the geological load increases. Then continue drilling. When the load is too heavy, lift the power head to reduce the load, to protect the drilling rig parts. When the load is reduced, continue to pressurize to prevent water or mud from entering the cut surface and reduce the friction coefficient.

5. Slip classification When drilling, due to the softening of mudstone, there will be two kinds of slippage. One is bottoming slippage, which is the so-called slippage phenomenon when drilling into the mud layer; the other is mudstone slippage. Since mudstone is hard, drilling and cutting are more difficult, and it slips under the lubrication of water or mud. There is a difference between the two slippages, so it is necessary to distinguish the slippage types to deal with them effectively.

6. Dealing with slippage It is very important to distinguish between the two types of slippage, and the treatment methods are also different. If the slippage is caused by the softening of mudstone, reverse the forward pressure to overcome it. If the slippage is caused by the water reducing the friction coefficient of the mudstone, it can be overcome through the above series of integrated methods. Mudstone has a large variation in strength due to differences in cementing materials and weathering degree, so not all mudstones can be drilled by cutting.

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