What factors affect the deviation of horizontal directional drilling rigs?

I. Equipment and Measurement Factors

1. Insufficient Guidance System Accuracy: Low-end or improperly calibrated guidance systems cannot provide accurate inclination and azimuth data, leading to loss of drilling direction control.

2. Rig Positioning Deviation: If the rig is not aligned with the centerline during installation, the initial angle error will amplify with drilling distance.

3. Improper Drill Bit Selection: Ordinary drill bits are prone to wear in hard rock formations, and unstable drill bits are prone to "drift" in soft soil formations, both of which can cause deviation.

II. Geological Conditions

1. Alternating Hard and Soft Formations: Uneven stress on the drill bit in rock formations of varying hardness can easily cause "head-up" or "head-down" phenomena, resulting in borehole undulation.

2. Gravel and Pebble Layers: Loose particles and weak cementation make the drill bit prone to slippage during drilling, making the trajectory difficult to control.

3. Fault Zones or Fissure Zones: Unstable formation structures can easily lead to drill bit suspension, deviation, or even mud leakage.

III. External Environmental Interference

1. Electromagnetic Interference: High-voltage lines, substations, underground metal pipelines, etc., generate strong magnetic fields that interfere with the magnetic azimuth data of the wireless guidance system, causing signal distortion.

2. Shallow-buried Section Disturbance: Vehicle traffic or construction vibrations may affect the stability of the surface soil, indirectly leading to borehole instability and trajectory deviation.

IV. Human Operation Factors

1. Insufficient Experience: Inaccurate judgment of guidance data by operators, failure to detect deviations in time, or adoption of incorrect correction strategies can easily cause reverse deviation.

2. Delayed Measurement: Failure to strictly adhere to the standard of "measurement every 3 meters of drilling" leads to accumulated deviations that are difficult to correct.

3. Inappropriate Parameter Settings: Excessive propulsion speed, excessively slow reflux speed, or mismatched thrust and torque will all reduce guidance response capability.

V. Role of the Mud System

1. Imbalance in Mud Performance: Too low viscosity results in poor wall protection, easily causing borehole collapse; too high viscosity results in poor fluidity, sluggish guidance response, and increased risk of "deviation".

2. Poor Circulation: Malfunctioning mud pumps or blocked return mud can cause sediment at the bottom of the hole and drill bit bouncing, affecting trajectory stability.

VI. Design and Management Factors

1. Inappropriate Trajectory Design: Insufficient radius of curvature and excessively steep entry/exit angles increase construction difficulty and the probability of deviation.

2. Lack of Complete Process Recording: Failure to record and verify parameters for each drill rod makes it difficult to detect trend deviations.