Hydraulic well testing inversion for modeling fluid flow in
fractured rocks using simulated annealing
Shinsuke Nakao 1), Julie Najita 2) and Kenzi Karasaki 2)
1) Geological Survey of Japan, 1-1-3 Higashi, Tsukuba, Ibaraki 305-8567, Japan. E-mail: nakao@gsj.go.jp
2) Lawrence Berkeley National Laboratory, USA.
Abstract
Cluster variable aperture (CVA) simulated annealing has been used as an
inversion technique to construct fluid flow models of fractured formations
based on the transient pressure data from hydraulic tests. A
two-dimensional fracture network system is represented as a filled regular
lattice of fracture elements. A hydraulic test is simulated on the lattice
with the finite element program TRINET. The algorithm iteratively changes
element apertures for a cluster of fracture elements in order to improve
the match to observed pressure transients.
This inversion technique is applied to hydraulic data collected at the
Raymond test site, California to examine the spatial characteristics of the
flow properties in a fractured rock mass. Nine boreholes were drilled in a
reverse V pattern with increasing spacing between boreholes with a maximum
distance of 60 m. Various geophysical logs, geophysical imaging techniques
and hydraulic tests have been conducted to image the hydrologic connection
of the fractured rock mass. Two major conductive zones have been detected;
one occurring near a depth of 30 m and the other between 54 to 60 m. Our
inversion results show that the practical range of spatial correlation for
transmissivity distribution is estimated to be approximately 5 ~ 10 m in
the upper extensive fracture zone.
raeg98@tansa.kumst.kyoto-u.ac.jp
Last modified: Wed Oct 14 09:45:59 1998