# Skin Value Analysis - PowerPoint PPT Presentation

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Skin Value Analysis. From “radial.dat” : Pdew point= 5899.3Psia The value that makes layer 1 and layer 2 reach dew point pressure at the same time is: S=250 Thus it’s not the expected value of S≈ 80that gives this result ( why? ) For S=250, Pdp is reached after around 450 days.

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Skin Value Analysis

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### Skin Value Analysis

• From “radial.dat” : Pdew point= 5899.3Psia

• The value that makes layer 1 and layer 2 reach dew point pressure at the same time is:S=250

• Thus it’s not the expected value of S≈ 80that gives this result (why?)

• For S=250, Pdp is reached after around 450 days.

• Even if they reach Pdp at the same time, the depletion of layer 1 and 2 after dp is NOT the same after dew point (normal?).

• It’s not possible to reach a plateau period for gas for such skin value.

### Simulation Results(Plots)

• I tried to plot some vectors to illustrate my previous comments related to skin value.

• I didn’t manage to plot on the same graph vectors from different layers (1 and 2). I already asked Silvya and she does not know how to do it with SensorView.Maybe I could ask Faiz or Alek how to do it?

• We are really limited with the vectors than can be plot with SensorPlot/SensorView; Could I use Sensor2Excel or StrExcel instead? (or something else?)The main point is to keep it “automatic”. Otherwise I could take the results and paste it in Excel in order to plot CGR for instance.

• See plots

Pressure:

Layer 1 ; S1=0

BHP limit reached

after 5000days

BHP limit is reached

in layer 1

after 5000days

Pressure:

Layer 2 ; S1=0

BHP in layer 2 is around

3000 Psia

(much higher than BHP limit)

Pressure:

Field ; S1=0

BHP average for the whole

field falls to 2000 Psia

Pressure:

Layer 1 ; S1=250

With such a skin value, BHP

in layer 1stays

higher than 3500 Psia (i.e. does not reach anymore

BHP limit as for S=0)

With such a skin value, BHP

in layer 1stays

higher than 3500 Psia

With such a skin value, BHP

in layer 1stays

higher than 3500 Psia

Dew point pressure is reached

in layer 1 around

450 days of depletion

Dew point pressure is reached

in layer 1 around

450 days of depletion

Dew point pressure is reached

in layer 1 around

450 days of depletion

Dew point pressure is reached

in layer 1 around

450 days of depletion

Pressure:

Layer 2 ; S1=250

BHP in layer 2 STILL stays

around 3000 Psia. Almost no effect of S1=250

due to “LNX” assumption (However final BHP is a little lower

to satisfy target gas rate)

Dew point pressure is reached

in layer 2 around

450 days of depletion

(same time as layer 1)

Pressure:

Field ; S1=250

BHP average for the whole

field falls to 3500 Psia

(much higher than

2000Psia for S=0)

GOR:

Field ; S1=0

Classical shape of GOR for

2 layers LNX reservoir

(showing changes in layers

contribution to GOR over time)

GOR:

Field ; S1=250

Linear increase of GOR over time.The peak value of 16000Mcf/d is

below the peak value of 20000Mcf/d

for S1=0

Linear increase of GOR over time.The peak value of 16000Mcf/d is

below the peak value of 20000Mcf/d

for S1=0

Linear increase of GOR over time.The peak value of 16000Mcf/d is

below the peak value of 20000Mcf/d

for S1=0

Qoil/Qgas:

Field ; S1=0

Plateau period is maintained

around 2500 days

at 25000Mcf/days

Qoil/Qgas:

Field ; S1=250

No plateau period is maintained.

With such high skin the well can’t

deliver 25000Mcf/days.

### Optimization (1): for target rate of 25000 Mcf/day

• As expected with previous plots and comments, the optimum value for NPV is not for S=250 (not when layer 1 and 2 reach Pdp at the same time).

• NPV max (Global!) is reached forS=5.625The increase in NPV value compared to S=0 is negligible!

• However as showed on next slides, it is possible to find a couple (S,D) to maximize NPV (Local maximum) by almost factor 10 compared to (S=0;D=0).

NPV Optimization (Target rate=25000 Mcf/day):

Variable: S

NPV Optimization (Target rate=25000 Mcf/day):

Variables: (S ; D)

Optimization (2): for target rate of 25000 Mcf/day

• How to know when we have reached the optimum value?

• I remember that when you showed me the optimization process, there were different colors for the different values of the objective function. How to display this option?

• I don’t see any physical meaning behind a local maximum such as: (15.234; 0.003952)?

• I am really unsure of the consistency of these results and I don’t understand phenomena behind this tremendous increase in NPV?

• How to plot the optimization results to get the shape of NPV versus (S;D)? As we have 2 variables the plot is a “surface”?