How then do we calculate the amount and size of solids that settle in the production separator?

As a first-order basis I use a mechanistic approximation detailed as follows.

- Calculate residence time of liquid (water) in vessel (weir height and inlet to weir distance)
- Calculate fall (capture) velocity as vertical distance divided by residence time
- Use Stokes Law to calculate size of particle matching capture velocity
- Particles with diameter greater than capture size are collected within the separator – smaller particles pass through with produced water
- Sum the total of all particles greater than cut off size gives total amount of solids settled in separator

An example is provided as detailed below.