Analysis and Treatment of Slippage Causes in Rotary Drilling Rig Mudstone Drilling

When rotary drilling RIGS are drilling mudstone or sandstone, slippage often occurs, meaning there is neither resistance nor pressure, making it impossible or difficult to drill, which affects the construction progress and production efficiency. After a long period of construction and experience accumulation, I have also participated in numerous mudstone geological foundation construction projects, such as those in Tianxingzhou, Hubei Province, Jialing River, Miluo, etc. I have a certain understanding and insight into drilling mudstone. Through geological research. Integration of drilling tools and operations. Finally, the problem of drilling mudstone was solved.

I. Overview of Mudstone

Red sandstone refers to sedimentary rocks such as mudstone, sandy mudstone, argillaceous sandstone, sandstone and shale, which are rich in oxides and appear red, dark red or brown. Red sandstone mainly presents two typical structural forms: granular clastic structure and argillaceous cemented structure. Most red sandstones can disintegrate and break under the influence of the atmospheric environment, and even become muddy. Therefore, the size of the rock blocks and the particle size distribution will change with the time process of the dry-wet cycle. Mudstone is a sedimentary rock formed by the solidification of mud and clay. Its composition and structure are similar to those of shale, but it is less likely to break. A kind of clay rock with indistinct bedding or foliation. Mudstone has the properties of water absorption and adhesion.

Ii. Causes of Slippage

During the construction process, if dry hole drilling is carried out in mudstone, the spiral drill bucket has a higher drilling efficiency. If a double-bottom sand hopper is used for drilling, it can also be drilled, but the load is relatively large. Once water comes into contact with the hole, slippage occurs immediately. Therefore, slippage is directly related to water or mud. The main reasons for slippage in mudstone are as follows: 1. The hardness of mudstone; 2. The lubricating effect of water or mud; 3. The softening of mudstone due to water absorption, etc.

Iii. Drilling Analysis with Different Drilling Tools

When the spiral drill bucket is drilling into the mudstone of the water hole, due to the softening of the mudstone upon contact with water, the conical head at the front end of the spiral drill bucket will be filled with mudstone debris, forming an integrated whole. As a result, the drill tool loses its drilling function and cannot continue drilling. Then, water or mud enters the space between the drill bucket and the mudstone to lubricate it, causing slippage.

When drilling mudstone water holes with a double-bottom toothed drill bucket, since the toothed drilling method uses the alloy head at the front end to drill in, the alloy head can easily break into the mudstone. However, as the alloy head at the front end is very short, the toothed body that fixes the alloy head must follow up and cut in. But if the toothed body is too blunt, it will form resistance. Since the toothed body breaks into the mudstone too shallowness and the mudstone is cemented, the crushing effect cannot be achieved. Therefore, continuous drilling cannot be carried out. Water or mud enters the space between the cutting teeth and the mudstone and lubricates them, thus causing slippage.

Through the above analysis, it is found that mudstone has good cementation and is not easy to break. To achieve the effect of cutting and breaking, a relatively sharp tool is required, and the drilling and cutting should be deep with low cutting resistance.

Four. Breaking through mudstone drilling

Therefore, the double-bottom sand hopper is selected, and the cutting drilling method is in line with the above analysis. However, in reality, the sand-picking hopper may also experience slippage, but this involves many factors

Defects on the drill bucket, such as the center positioning tip not being too long, too wide or too blunt, the Angle of the tooth tip and the gap between the tooth seats, the diameter of the edge teeth, the model of the bucket teeth or the wear of the tooth tip, are best improved to reduce the height difference of the tooth tip length and the contact area.

2. The diameter of the sand-grabbing hopper: The larger the diameter of the hopper, the greater the contact area and the more difficult it is to overcome slippage. Therefore, for larger pile diameters, a smaller diameter hopper can be selected for drilling first.

3. Overcoming Slippage Analysis As mentioned earlier, the main cause of slippage is lubrication by water or mud. Therefore, as long as the softened mudstone and the water or mud on its surface are overcome, the slippage of mudstone can be overcome! After overcoming the problem, continuous drilling is necessary. In this way, water or mud cannot enter the cutting surface. As a result, the tooth tips remain in contact with dry geological conditions, allowing for normal drilling.

4. Operation control is of great significance. Due to the hardness and good cementation of the mudstone, it is not easy to cut in under the lubrication of water. First, raise the power head to the highest position. Then, it is necessary to control the power head to rotate slowly. The pressurization speed should be slow but continuous. The power head and the pressurization speed must be well coordinated. If the pressurization stroke is completed and the mudstone has not been cut in, raise the power head again and continue drilling Continue drilling until the geological load rises. When the load is too heavy, the power head needs to be lifted to reduce the load and protect the components of the drilling rig.

When the load is reduced, further pressure should be applied to prevent water or mud from entering the cut surface and thereby lower the coefficient of friction.

5. Slippage classification: During drilling, due to the softening of mudstone, two types of slippage phenomena may occur. One is the bottom slippage, which is also known as the slippage caused by soil dropping during drilling in the mud layer. Another type is mudstone slippage. Due to the hardness of mudstone, drilling and cutting are inherently difficult. However, under the lubrication of water or mud, slippage occurs. There is a difference between the two types of slippage. Therefore, it is essential to distinguish the type of slippage in order to handle it effectively.

6. Dealing with slippage: It is crucial to distinguish between two types of slippage, and the treatment methods are also different. If the slippage is caused by softening the mudstone and supporting the bottom, then reverse the forward transmission pressure to overcome it. If the slippage is due to the hard mudstone and the reduced friction coefficient by water, it can be overcome through the above series of integrated methods. Due to the differences in cementing materials and weathering degrees, the strength of mudstone varies greatly. Therefore, not all mudstones can be drilled by cutting.