Difference between revisions of "Injectivity index"

Revision as of 12:21, 27 August 2026

I - well injectivity index characterizes how much water a well can inject per unit of pressure drop.

I is defined as follows:

{I} = \frac{q_{inj}}{P_{wf} - \bar{P}}

Thus, injection rate could be calculated as:

{q_{inj}} = {I}(P_{wf} - \bar{P})

From Darcy's law for an unfractured injection well located in the center of a circular drainage area, the I in pseudo-steady state is:

{I} = \frac{kh}{141.2 B \mu} {J_D} = \frac{kh}{141.2 B \mu} \times \frac{1}{ln{\frac{r_e}{r_w}-\frac{3}{4}+S}}

B

= formation volume factor, bbl/stb

I

= injectivity index, stb/psia

J_D

= dimensionless productivity index, dimensionless

kh

= permeability times thickness, md*ft

\bar{P}

= average reservoir pressure, psia

P_{wf}

= well flowing pressure (bottomhole), psia

q_{inj}

= injection rate, stb/d

r_w

= wellbore radius, ft

r_e

= drainage radius, ft

S

= skin factor, dimensionless

\mu

= viscosity, cp

@@ Line 21: / Line 21: @@
 :<math> \bar{P} </math> = average reservoir pressure, psia
 :<math> P_{wf} </math> = well flowing pressure (bottomhole), psia
-:<math> q_{inj} </math> = injection rate, stb/d or Mcf/d
+:<math> q_{inj} </math> = injection rate, stb/d
 :<math> r_w </math> = wellbore radius, ft
 :<math> r_e </math> = drainage radius, ft