Water Injection Performace

Water Injection Performance Calculation


This is a brief summary to calculate or estimate the injection well performance. Injection well is the well that will have fluid flow from the surface into the reservoir. Injection well is the reverse condition of production well that flows from the reservoir to the surface. The injection well performance calculation then also will use the productivity index of production well but it will means that pressure gradient is in opposite direction.

Productivity index of the production well:
Productivity Index =


J =

J is in stock tank barrels per day per psi of drawdown.
The productivity index represents the dynamic response of the reservoir and its fluid properties within the drainage area of a specific well. It defines the relationship that exists between flow rate, q, and bottomhole flowing pressure, pwf, for a given average reservoir pressure, R. The productivity index is constant when flow parameters like permeability are constant. When bottomhole flowing pressure is above the bubble point the productivity index will be constant. As the pressure drops below the bubble point, however, the productivity index will decrease as gas comes out of solution, changes permeability values, and inhibits flow.

For injection well, it becomes:
Injectivity Index = Jin =





From this equation we can develop the injection flow performance (Pwf versus injection rate ) as you can see the curve below:














Usually we have to consider the formation fracture pressure so our fluid injections will not going to anywhere that could risk to the environment, and to make sure our fluid goes to our desired formation. Then you can put the line on the injection performance curve above where the pressure limitation of your injection to avoid formation fracturing.