Tubular Lockup Prediction

Answer the planning question directly: will the tubing reach target depth, and if not, where will it lock up? Enter the well trajectory, tubular, fluids, friction and injector capacity and get lockup MD, force margin, helical buckling onset and a friction-sensitivity table.

What the model does

A Johancsik soft-string torque-and-drag integration from the string end to surface, running in hole, with contact force from inclination and build-rate curvature, effective submerged weight that separates steel, internal fluid and displaced annular fluid, post-helical wall contact (Mitchell) and Dawson-Paslay, Chen-Lin-Cheatham and Lubinski buckling limits. Required injector push is reported as a positive magnitude; lockup is the first depth at which it reaches injector capacity or helical drag runs away, with the governing mechanism stated.

Outputs that plan a job

• Target status — REACHABLE with depth reserve, or LOCKUP BEFORE TARGET with shortfall
• Predicted lockup MD, projected beyond target along the hold section to a stated limit
• Required push at TD, injector capacity, force margin and utilisation
• Helical buckling onset, reported separately from lockup
• Maximum friction coefficient for reaching target, and a friction-sensitivity table
• Nominal versus friction-reducer comparison

Scope

Straight-hole buckling criteria applied locally in curved sections, a single Coulomb friction coefficient, no pressure-area terms, no fluid drag or tortuosity. A screening tool for coiled-tubing and small-diameter tubular reach; the page states what it has not been validated against.

Frequently asked questions

How do I calculate coiled tubing lockup depth?

Integrate the axial force along the string with a soft-string drag model, compare compression against sinusoidal and helical buckling limits, add post-helical wall contact drag, and find the depth at which the required surface push reaches the injector capacity. This tool does that from trajectory, tubular and friction inputs.

What is the difference between helical buckling and lockup?

Helical buckling onset is where compression first exceeds the helical criterion; the string can still advance. Lockup is where the friction generated by the buckled string means the injector can no longer push it further. The tool reports both depths separately.

How much does friction reducer extend reach?

The tool compares a nominal and a reduced friction coefficient side by side and reports the largest friction coefficient at which the target is still reached, so the value of a friction reducer is quantified for the specific well.

Can I use it for drill pipe or completion tubing?

The mechanics are generic soft-string mechanics with the tubular OD, wall, modulus and densities as inputs, but the buckling criteria and validation are oriented to coiled tubing and small tubulars; treat results for larger strings as screening only.