Pressure Drawdown (∆P) is defined as the difference between the static bottom hole pressure (SBHP) and the flowing bottom hole pressure (Pwf). Thus, the drawdown is the differential pressure that drives fluids from the reservoir into the wellbore.
∆P= Pressure drawdown = SBHP – Pwf
If SBHP = 200 bar, and Pwf = 80 bar; therefore the Pressure drawdown (∆P) = 200 – 80 = 120 bar.
The amount of pressure drawdown dictates the amount of flow into the wellbore or production. The higher the pressure drawdown is, the higher the production rate. The drawdown, and therefore the production rate of a producing interval is typically controlled by surface chokes.
NB: Reservoir conditions, such as the tendency to produce sand, may limit the drawdown that may be safely applied during production before damage or unwanted sand production occurs.