Injectivity index

Brief

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

Math & Physics

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:

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

Nomenclature

$B$ = 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

Greek symbols

$\mu$ = viscosity, cp

See Also

• Darcy's law
• J
• Hall Plot