# Intelligent Stuck Pipe Type Recognition Using Digital Twins and Knowledge Graph Model
## Materials and Methods
### Recognition of Sticking Rules Based on SAX Morphology Aggregation Method  
#### 2.2.1 Mechanism and Rule of Different Types of Sticking  
Sticking is mainly divided into sticking due to cuttings bed, fall-block, differential pressure, hole shrinkage, collapse, and key seat [28]. Mechanism of different types of sticking:  
Sticking due to key seat: A cylindrical groove is produced on the well wall (called key seat) due to long-term contact between the drill string and the well wall, rotary friction, and the scratching of large drilling tool at the time of pulling out of the hole/running in hole in the place with a large change in hole drift angle and azimuth angle. The dogleg key seat is generally smaller in diameter than the drill bit, and slightly larger in diameter than the joint. At the time of pulling out of the hole, the drill bit or large drilling tool will get stuck in the key seat, resulting in sticking due to the key seat. The thick shale is found to be mixed with sandstone under some special stratum conditions. After well drilling, the shale collapse causes the hole diameter to expand, while the sandstone maintains the original \begin{table}
\begin{tabular}{c c c} \hline \hline
**p** & **a/a\({}_{\text{m}}\)** & **b/b\({}_{\text{n}}\)** \\ \hline
94.4\% & 12.8 & 230.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Degree of stuck pipe for well M.  
Figure 4: Distribution of measured and calculated POOH hookload before stuck pipe. Figure 5: Distribution of measured and calculated POOH hookload while sticking. well diameter. When the drill string leans to the lower edge of the hole, it is supported laterally only by the protruding sandstone and the key seat is formed by the protruding greywacke. At the moment of pulling out of the hole, the drill pipe joint is prone to getting stuck in the greywacke key seat. Sticking due to differential pressure: At the time of normal drilling, the solid particles in the mud gradually accumulate on the well wall to form mud cake, thus the pore pressure of the mud cake can be considered to be the same as that of the drilling fluid column at the same depth. When the drilling stops, the drill string in the horizontal section of the horizontal well will lie flat on the well wall and the moisture in the mud cake will be gradually pushed into the stratum by the drill string, causing the pore pressure of mud cake gradually decreases until being the same as the stratum pressure. However, the stratum pore pressure gradient is inconsistent in the same open hole section, the fluid column pressure must be able to balance the maximum formation pressure in the interval, the positive differential pressure will be formed in the stratum with low pressure gradients, and the drilling tool will be gradually pressed into the mud cake by the pressure difference, making the sticking due to differential pressure more serious. Sticking due to cuttings bed: If the drilling cuttings fail to be taken out of the drill pipe in a timely manner when the displacement and the drilling rate do not match the well at the time of drilling rapidly in the horizontal section, the rock debris will settle to the lower edge of the horizontal section to form the cuttings bed. At the moment of drilling, the cuttings bed will increase the revolving resistance of the drill string and the torque, resulting in sticking. At the time of pulling out of the hole and running in hole, the large diameter tools (such as stabilizer and drill pipe joint) will push the rock debris in one direction for extrusion like a \"bulldozer\", very easily giving rise to sticking. The principal factors of forming the cuttings bed can be summed up as follows: 1 The cuttings bed is formed because the drilling fluid does not circulate for a long time and the rock debris particles gradually sink to the horizontal section. 2 The cuttings bed is gradually formed because the rock debris is formed quickly at the time of drilling quickly and the displacement fails to meet the well cleanliness standard.