Due to the complexity of drilling through the formation, equipment installation, drilling operations, measurement errors of the sink wall sinking link, etc., it is still difficult to avoid the deviation of drilling and well formation. Therefore, when determining the diameter of the drill, the bore deflection should be considered.
The effect of wellbore and well deflection on the permanent use of the wellbore. In order to ensure the verticality of the wellbore, the diameter of the borehole is generally expanded by the deflection slope allowed by the construction specification multiplied by the depth of the well. For the main and auxiliary shafts and the wellbore with lifting requirements, the inner diameter of the wellbore should be properly expanded to ensure that the effective circular section meets the lifting requirements. At present, for the lifting wells with a depth of 400-600 m and an alluvium thickness of 350-550 m, the inner diameter expansion value is generally 200-300 mm. For example, the two main wells of Longgu Coal Mine have an inner diameter that has been expanded from 5.5m to 5.7m. The main shaft and inner diameter of the plate coal mine have been expanded from 6.5m to 6.8m.
In summary, the determination of the drilling diameter can be calculated as follows:
Where D2 - drilling diameter, m;
D--wellbore design diameter (including the diameter of the hoistway diameter expansion), m;
E--well wall design thickness, m;
E--filling gap after wall, e=d+B,m;
D--the maximum outer diameter of the outer filling pipe, m;
B--safety clearance, generally taking 0.10-0.20m;
H2--drilling depth, m;
A--the slope of the drilling, 0.5风 for the wind shaft and 0.8‰ for the lifting well;
A--the diameter of the wellbore is generally 0.15-0.3m.
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