Productivity Index (PI)

The productivity index is defined as the flow rate per unit pressure drop, and serves as an indication of the production potential of a well. It is defined as:

For example, if a well flows at a 1,000 stbbls/d with a flowing (sandface) pressure of 1500 psi and at an average reservoir pressure of 2,000 psi, then the productivity index is:

PI = 1000 / (2000 - 1500) = 2 stbbls/d / psi

After the PI is known, the equation can be rearranged to determine the deliverability rate as follows:

This equation is only valid for a well in an undersaturated reservoir. For wells in saturated reservoirs, or for gas wells, the relationship is not as straightforward, and the simple relationship described above does not apply. In these situations, either an IPR (for oil) or AOF (for gas) analysis should be performed.