Passability modeling and field verification of sand screen completion strings

Running sand screen completion strings to target depth is challenging in horizontal and extended-reach wells because drag, string stiffness, borehole curvature, cuttings accumulation, and borehole shrinkage can jointly reduce passability and cause sticking. This study develops an integrated passability prediction and diagnostic workflow that combines a torque-and-drag model considering cuttings-bed-enhanced friction and buckling-induced contact force, a deformation-energy-based stiffness-matching model, and an elastic geometric-compatibility model for large-diameter downhole attachments. The workflow was applied to Well H in the Kenli 10-2 Oilfield, where the sand screen completion string became obstructed at a measured depth of 3316 m and could not pass the interval even under a maximum set-down load of 35 t. Initial analyses indicated that the string should theoretically reach the target depth, with a predicted hook-load margin of 62.67 t, a stiffness ratio greater than 1.0, and a minimum sliding-sleeve passable curvature of 8.18°/30 m. However, the apparent open-hole friction coefficient inverted from field hook-load data reached approximately 3.5, whereas the cuttings-bed-corrected friction coefficient increased only from 0.50 to 0.59, indicating that ordinary friction and cuttings accumulation were not the dominant causes. Further shrinkage analysis showed that a 2.2% shrinkage ratio reduced the effective borehole diameter below the sleeve outer diameter. Therefore, local borehole diameter reduction in the mudstone interval was identified as the primary sticking mechanism. After hole-enlargement reaming, the original sand screen completion string was successfully deployed, verifying the proposed workflow. The proposed workflow provides a practical approach for predicting passability, diagnosing sticking mechanisms, and designing remedial measures for sand screen deployment in complex wells.