neqsim-erd-reach-screening

ERD Reach Screening

Use this skill for a public, screening-level answer to "can this rig reach that far?". It builds a build-and-hold well path, integrates a soft-string torque and drag model with Coulomb friction, and returns the torque-limited reach for a drill string and friction case. It is meant to be calibrated to the longest well already drilled from the same rig before any reach number is quoted.

When to Use

• A keeper, exploration or infill well is proposed from an existing platform or fixed rig and the horizontal departure is large compared with the rig's history.
• A reach-versus-friction-factor curve is needed to turn friction uncertainty into a probability that the well can be drilled.
• A team wants to know whether a heavier or higher-torque drill string (for example 6-5/8 in) moves the reach limit enough to matter.

Inputs

• tvd, departure in metres below the rig floor and horizontally from the slot.
• WellEnvironment: kick-off point, build rate (deg per 30 m), mud specific gravity, cased and open-hole friction factors, casing shoe fraction.
• DrillString: drill pipe, HWDP and BHA weights per metre, tool-joint radius, torque limit.

Outputs

• ReachResult: measured depth, hold inclination, ERD ratio (departure over TVD), pick-up and slack-off hook load, torque on bottom, which limit binds (torque or slack-off (lock-up)).
• reach_limit(...): the largest departure that keeps torque within the limit and slack-off positive.

Engineering Method

1. Build-and-hold path from the kick-off point at a constant build rate; the hold inclination follows from the target departure.
2. Johancsik soft-string integration from the bit up: axial load changes by the buoyed weight component plus or minus friction times the contact force; torque accumulates friction times contact force times tool-joint radius.
3. Calibrate the friction factors so the model just allows the rig's longest historic well (for Njord A on the Norwegian shelf this gave 0.15 cased and 0.20 open hole, a limit about 20 percent above the 5.1 km actually drilled), then scale friction to express uncertainty.