## Challenges

Some initial challenges to the modeling community are presented below

### Modeling Challenges

**1. **Outline method to estimate friction and fluid damping parameters. The mass and stiffness parameters of most models are easy to determine analytically. However the friction and damping effects are difficult to determine and must be estimated from drilling data. The goal is to develop methods and workflows to minimize the error between models and drilling data. This will be useful in; optimizing control systems, design of tools, and modeling transient events such as slide to rotate, going to bottom, etc

- Minimize model errors – response amplitude, frequency
- Include parameter sensitivity studies
- Include recommendations on data gathering – i.e. rotate to store torsion, stop, then restart to estimate static friction

**2. **Create a 6 axis drill BHA and drillstring model that includes the effects of wall climbing during rotations. Use this model to study effect of wall friction, hole angle, RPM and hole patterns on reverse drill string whirl.

**3. **Create Basic 4 Control Loop Auto Driller Control Systems

- ROP, WOB, Differential Pressure, Torque
- With and without Bumpless transfer between loops
- Use different control logic PID, MPC, Bang-Bang
- Include set points as well as safety limits (stop drum and disengage AD)

**4. **Create a Top Drive Controller

- Include stall Limits
- Post stall behavior – hold torque / torque dissipation
- Add active torsional damping – Soft Speed, Soft Torque, Z-Torque

**5. **Create Model Set Up file format to: Start Flow, Pick up, Slack off, Rotate, Ream up, Ream Down, Drill – in any order, with ramp rates

**6. **Include fluid accelerations and dynamics in SPP estimation

**7. **Upgrade motor model to include mud blow by (RPM drop with pressure) and stalling limits

### Numerical Challenges

- Numerical stability with wellbore contact
- Fast transient dynamic stiff string model
- Numerical stability of the drilling process in different formations
- Post buckling drill string behavior