Pressure and Rate Controls
The well solver supports two types of control, namely, pressure control and rate control.
If pressure control is chosen, we add the following constraint for the pressure of the top segment of the well:
In this case, we check that at each iteration of the Newton solver, the rate at the top of the first segment is smaller than the maximum rate specified by the user.
If this is not the case, we switch to rate control.
If rate control is used, we add the following constraint for the rate at the top of the first segment, denoted by :
For an injector well, if the pressure at the top segment becomes larger than the target pressure specified by the user, then we switch to pressure control. Similarly for a producer well, if the pressure at the top segment becomes smaller than the target pressure specified by the user, then we switch to pressure control.
To summarize, the compositional multiphase flow solver assembles a set of equations, i.e., mass conservation equations and 1 volume constraint equation in each segment, plus 1 pressure relation at the interface between a segment and the next segment in the direction of the well head.
For the top segment, the pressure relation is replaced with the control equation.
Number of equations |
Equation type |
|
Mass conservation equations |
1 |
Pressure relation or control equation |
1 |
Volume constraint |