Environmental Engineering Reference
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0.030
Analog field: 20 good wells out of 100
0.025
0.020
P
(New = analog | no data) = 0.5
0.015
0.010
New field is the same as analog
0.005
0.000
0
10
20
30
40
50
Number of drilled wells in the new field
Figure 13.46
Value of information versus number of test wells in developing an unconventional gas reservoir.
case where all 50 test wells in the new field are good. Since the analog field with only 20 good
wells out of 100 is directly relevant, the combined data give 70 good wells out of 150 total
wells, which are still well below the break-even frequency of 0.83 in the new play.
This case-history application illustrates the following key points:
1. It is not reasonable to assume that prior probability distributions can be established
based entirely on experience because that precludes the possibility of events beyond
our experience.
2. The value of test wells in this risky play is enhanced when leaving open the possibility
for profit even though available information from analog fields are not encouraging.
3. There is a balance between relying entirely on experience (i.e., historical data from
analog fields) versus not relying on it at all.
13.5.4 qa/qC testing
Figure 13.47
shows a geomembrane liner being installed for waste containment; the geo-
membrane panels are welded together to form seams. QA/QC testing for the installation
involves taking destructive samples of the seams and measuring their strength. For destruc-
tive samples that fail the strength test, additional destructive samples are taken to bound
and then repair the length of the defective seam (
Figure 13.48
).
Figure 13.47
Installing geomebrane liner by seaming panels together in the field.
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