ABSTRACT: Reservoir Delineation of the Sibayak Geothermal Field, Indonesia Derived from Resistivity and Magnetotelluric Data
Daud, Yunus1, Keisuke Ushijima2, Sayogi Sudarman3,
and Bambang Soegijono4
(1) Exploration
Geophysics
Laboratory, Department of Earth
Resources System Engineering, Faculty of Engineering, Kyushu University, Fukuoka, Japan
(2) Exploration
Geophysics
Laboratory, Department of Earth Resources System Engineering,
Kyushu University, Fukuoka, Japan
(3) Geothermal Division, Pertamina, Jakarta, Indonesia
(4) Department of Physics, Faculty of Mathematics and Natural Sciences, University of
Indonesia, Depok, Indonesia
Sibayak Geothermal Field is located in the North Sumatera Province, Indonesia.
Reconnaissance survey had been started since 1989 by Geothermal Division of Pertamina
continued by detail geophysical exploration
in 1990 including electrical resistivity. The
exploration
results suggested that the Sibayak area is a high potential geothermal field.
To delineate the resistivity distribution to the economic depth, magnetotelluric (MT)
measurements were carried out in 1992. This paper presents the result of a
multidimensional interpretation of the electrical resistivity and MT data that was
performed in an attempt to delineate the complex conductivity structures of the geothermal
area and to gain information of the geothermal reservoir. Key resistivity soundings were
interpreted using a 2.5D finite-difference algorithm modified from Dey_fs method. The MT
data were interpreted using a 2D finite element code. A conductivity model was developed,
integrating available geological and drill-hole information. The combined interpretation
of the resistivity and MT data for several sections shows that a thick conductive layer is
commonly found in the study area underlain by a resistive layer. The former is associated
with the strongly altered rock (cap rock) and the latter is associated with the moderately
altered reservoir layer. It is proven from the study that the combined resistivity and MT
data interpretation can effectively delineate the reservoir structure of the Sibayak
Geothermal Field.
AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia