Inflow performance of a reservoir is defined as the functional relationship between the flowing bottom-hole pressure and the resulting flow rate. It is the rate at which fluid will flow towards the wellbore and depends on the viscosity of the fluid, the permeability of the rock, and the driving force. 

Or The performance curve of upstream

equipment is called inflow performance.

Outflow Performance involves fluid flow through the production tubular, then wellhead and then surface flow line. In general the fluid flow involves the pressure difference across each segment of the fluid flow.

Or The performance curve of downstream

equipment is called outflow performance.

The intersection of the two performance curves is called operating point.

i.e. it tells us the operating flow rate and pressure.

There are two commonly-used quantities to represent reservoir inflow performance:

Productivity index (PI) Inflow performance relationship (IPR)

It is special type of measurement property which is used to measure life and productivity of reservoir.

Inflow performance relationship is useful as a tool monitor well performance and predicts the simulation and artificial lift requirements of a number of wells.

In order to check or correct the size of a well to an accurate value IPR of a well must be known.

The current inflow performance relationship (IPR) must be known to determine the potential for additional production.

Measure of the ability of the well production is the Productivity Index.

The relationship between well inflow rate and pressure drawdown can be expressed in the form of a Productivity Index

It is the magnitude of slope of IPR curve denoted by PI or J

It is important to keep track and analyze the plot of production rate vs. time and perform decline curve analysis. This can be used to determine if the well is declining normally or if it is experiencing abnormal decline.

The system analysis for determination of fluid production rate and pressure at a specified node is called ‘‘Nodal analysis’’.

Whole production system is divided into small elements or nodes.

Pressure is assumed constant at each node. Pressure vs production rate curves are plotted. Used for optimization of production system.