-
Not Synced
Speaker: Nay wells are affected by a well
skin, a low permeability layer that
-
Not Synced
surrounds the well and causes the drawdown
in the skin to be less than- er to be
-
Not Synced
greater than the drawdown that
would be expected otherwise.
-
Not Synced
So, we can see this in the, in the sketch.
-
Not Synced
This line here is the expected drawdown
using, uh, the Jacob analysis, or
-
Not Synced
perhaps some other analysis, but as we
get right in the vicinity of the well, we
-
Not Synced
see that there's a low permeability zone
here, and the head goes like so, follows
-
Not Synced
this dashed line.
-
Not Synced
And as a result, this is the expected
drawdown based on our theoretical analysis.
-
Not Synced
It is using the properties of the aquifer,
uh, out here away from the well
-
Not Synced
[stammering] in this region, but in fact
we observe that the drawdown at the well
-
Not Synced
is here, so the drawdown is greater, um,
and that results from the extra headloss
-
Not Synced
due to the well skin.
-
Not Synced
So we want to characterize this, and one
way to characterize it is to use the well
-
Not Synced
efficiency, which is the ratio of the
expected drawdown from our theoretical
-
Not Synced
analysis to the observed drawdown,
what actually occurs in the field.
-
Not Synced
So we need a way to calculate what the
expected drawdown is, and we can do
-
Not Synced
this with the Jacob analysis.
-
Not Synced
What I'm showing here is a version of the
Jacob analysis that's set up to calculate
-
Not Synced
the head- er I guess this is the drawdown
here, um, as a- at a particular time.
-
Not Synced
So, the important thing to recognize is
right here.
-
Not Synced
The radial distance that we're using here
is the radius of the well.
-
Not Synced
What we used in the previous analysis
was the radial distance of the monitering
-
Not Synced
well, where our data were made.
-
Not Synced
In this case, we need to use the radial-
the radius of the well itself.
-
Not Synced
This time here, that's the time, the
elapsed time, for a data point that we're
-
Not Synced
gonna use to determine the observed
drawdown.
-
Not Synced
The calculation goes like so: we put in
the observed time and the radius
-
Not Synced
of the well, and everything else is pretty
much the same, the s and the t we've
-
Not Synced
calculated using a monitoring well out
here in the formation.
-
Not Synced
The performance here of the monitoring
well, the head in the monitoring well, is
-
Not Synced
not effected by the skin, so when we
calculate TNS from the monitoring well
-
Not Synced
data, we're getting something that's
really just affected by the, um,
-
Not Synced
formation properties.
