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The purpose of this study is to use well logging data to
estimate parameters of formation strength of aquifers in
south-western coastal area of Yun-Lin. The information of
these parameters can be used for evaluating failure of a
wellbore, sand control of water production and land subsidence
problems. This study is integrating the theories in
literature, using formation density log and sonic log data to
calculate shear modulus (G), bulk compressibility (Cb). The
main works of this study are : (1) well logging data analysis,
(2) identification of aquifer sand, and (3)calculation of the
parameters of formation strength. The well logs of
three wells(Ths-5, Ths-8, and Gh-1) are analyzed in this study
to estimated the parameters of formation strength. There are
seven aquifers identified in Ths- 5 well between 30 and 320
meters. In Ths-5 well, the ranges of shear modulus are 0.17 ~
0.43*106 psi (average value is 0.254*106 psi); the ranges of
bulk compressibility are 0.99 ~ 2.4*10-6 psi-1 (average value
is 1.74*10-6 psi-1). There are six aquifers identified in
Ths-8 well between 310 and 500 meters. In Ths-8 well, the
ranges of shear modulus are 0.15 ~ 0.42*106 psi (average value
is 0.267*106 psi); the ranges of bulk compressibility are 1.2
~ 2.6*10-6 psi-1(average value is 1.681*10-6 psi-1). In
Gh-1well, there are six aquifers identified between 310 and
500 meters. The ranges of shear modulus is 0.18 ~ 0.38*106
psi(average value are 0.278*106 psi); the ranges of bulk
compressibility are 1.3 ~ 2.5*10-6 psi-1(average value is
1.763*10-6 psi-1). From the results of this study, shear
modulus in aquifers increases as depth increase, from the
average of 0.188*106 psi in the interval of 30 to 50m depth
to the average of 0.319*106 psi in the interval of 485 to
494m. Bulk compressibility decreases as depth increase, from
2.27*10-6 psi-1 in the shallowest aquifer to 1.39*10-6 psi-1
in the deepest aquifer at about 500m.
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