# 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
3 When the drilling fluid returns to some intervals with a large hole diameter, the rock debris tends to accumulate here. When a certain angle is reached, the rock debris will collapse and migrate to the bottom of the horizontal well, burying the lower drilling tool and forming the cuttings bed. Sticking due to collapse: 1 Geological factor: Original crustal stress: After the well has been drilled through, the stress field around the well is resolved anew. When the hydrostatic column pressure cannot balance the stratum lateral force, the stratum will collapse. Rock property: The stability of sedimentary rocks varies due to the different cementation degree, burial time, and depositional environment of sedimentary rocks, so the well wall collapse will easily occur when drilling the glutenite with poor cementation, the shale with joint development, and the crush zone formed by a fault. 2 Physical and chemical factors: The hydrostatic pressure, hydration expansion, and capillary action are the main factors incurring the well wall collapse. When the drilling fluid filtrate immerses into the shale (clay) interior, the pore pressure, expansion pressure, etc. will be produced, with the structure of the clay weakened and linear decrease in its strength, resulting in collapse. 3 Drilling fluid factor: When the return velocity of drilling fluid in the annulus is high, it will be under the turbulent condition, which will cause impact on the well wall, giving rise to well wall collapse. Reducing the drilling fluid density to improve the drilling rate will cause the hydration expansion of the stratum, resulting in well collapse. At the moment of increasing the drilling fluid density to make the well wall stable, the stratum will be easily fractured, so the density design of drilling fluid is very important for well wall stability. Sticking due to hole shrinkage: 1 The moisture of the stratum creep shale fails to be discharged in a timely manner under the action of surrounding environment in the process of sedimentation, so the state of under-compaction exists in the compacting process. When drilling the stratum, the shale with water will creep rapidly towards the well due to the influence of the overlying strata pressure, resulting in hole shrinkage. 2 The drilling fluid is capable of balancing the drill pipe pressure and keeping the well wall stable. When the drilling fluid density is low, the well wall will collapse or creep toward the center of the drill pipe, resulting in sticking due to hole shrinkage. When the density of drilling fluid increases, the hole shrinkage deformation rate of the well will gradually decrease, thus the critical value of drilling fluid density can be known by the curve of drilling fluid density and hole shrinkage deformation rate. If the drilling fluid density configured is greater than the critical density, sticking due to hole shrinkage can be avoided to a great extent. Sticking due to fall-block: The mudstone section is very stratified, with slow drilling rate and long construction period, and the immersion of the open-hole section by the drilling fluid for a long time results in well wall instability. Once the large upper well wall fall-block is stuck between the bottom drill pipe joint and the lower well wall, the unsmooth local circulation will result in accumulation of rock debris, quickly causing the fall-block to get stuck between the drill string and the well wall. The essential reason of the fall-block is the slight well wall instability. The following sticking laws and characteristics are obtained by the statistics of sticking laws in Sichuan and Chongqing. Mechanism and rule of different types of sticking are shown in Table 5.