## 3 Theoretical Analysis of the Anchoring Action of Oil Wells on the Movement of Overburden Rock  
### Mechanisms Affecting Anchoring in Oil Wells  
Oil well anchoring technology establishes a stable support system between the wellbore and the surrounding overburden through cementing, mechanical anchoring, and casing support. Anchoring technology creates a mechanically stable structure around the wellbore through the combined action of casing and cementing, regulating stress distribution within the formation (Figure 3) and enhancing wellbore stability. During drilling, the original formation stresses are disturbed, leading to high-stress concentration zones, and anchoring techniques redistributing stress and mitigating localized stress concentrations. Cementing creates an annular sealing structure between the wellbore wall and the formation, dispersing formation stress and preserving wellbore integrity. This reduces the risk of wellbore collapse in loose sand formations or high-pressure, low-permeability reservoirs, while also improving long-term wellbore stability and mitigating wellbore damage caused by stress fluctuations during oil and gas production. The elastic mechanics model is applicable for analyzing the stress distribution along the wellbore wall, particularly in deep formations. Using the theory of thick-walled cylinders and accounting for the stress conditions on the wellbore wall due to internal and external  
Figure 3: Oil well casing force model. Figure 2: Oil well body profile and location of oil well clusters in relation to the workings. pressures [29], the normal stress distribution in a cylindrical wellbore can be determined using the following equation:  
\[\sigma_{n}=\frac{P_{out}r_{2}^{2}-P_{in}r_{1}^{2}}{r_{2}^{2}-r_{1}^{2}} \tag{1}\]  
In the formula, \(r_{1}\) and \(r_{2}\) represent the inner and outer diameters of the wellbore, taken as 0.1 m and 0.2 m, respectively. \(P_{out}\) and \(P_{in}\) denote the external and internal pressures of the wellbore, respectively. In the Yan'an Zichang region, the internal wellbore fluid pressure is 25 MPa, while the external formation pressure is 12.5 MPa. Substituting these values into the equation, the normal stress is found to be positive, indicating that the wellbore wall is subjected to compressive stress. During the cementing process, the cement slurry fills the annular space between the wellbore and the formation, forming a high-strength cement sheath that effectively seals fractures around the wellbore. Once cured, the cement withstands the stresses associated with formation fracture propagation, preventing further fracture propagation near the wellbore, preventing reservoir fractures from intersecting the wellbore, reducing interformational fluid migration, and mitigating formation instability induced by reservoir pressure fluctuations, particularly in high-pressure gas reservoirs and multi-fractured zones. The casing and cementing system collectively support the overburden, mitigating its settlement by uniformly transmitting formation pressure to deeper, stable strata. Casing support distributes overburden pressure and reduces formation stress around the wellbore. During resource extraction, deformation equilibrium of the formation around the wellbore is maintained through the compressive strength of the cement sheath, which improves the uniformity of formation pressure transmission, mitigates overburden damage due to localized overloading, and provides structural reinforcement for complex multi-layer formations, such as salt formations and coal-bed methane reservoirs. The anchoring system maintains a strong bond between the wellbore and the surrounding formation during long-term operation, preventing casing and cement dislodement caused by thermal expansion, contraction, or geological deformation.