ABSTRACT: Seismic
inversion
modeling
and attribute analysis for reservoir
characterization
Ronghe, Sagar1 and Korakot Surarat2
(1) University
Brunei Darussalam, Bandar Seri Begawan, Brunei
(2) PTT Exploration and Production Co Ltd,
Bangkok, Thailand
Results of seismic
inverse modelling and attribute analyses were integrated to
characterize the depositional sequence, location and geometry of clean sand facies in an
onshore producing half-graben basin in Thailand. The target interval was deposited in a
lacustrine setting subject to occasional fluvial influence. Petrophysical crossplots
revealed clean sand to have higher acoustic impedance, higher resistivity, and lower
neutron porosity than shale. Acoustic impedance was determined to be a unique indicator of
lithology, but not of hydrocarbon. Crossplots within sub-units of the target interval
enabled the determination of acoustic impedance ranges for clean sand, shaly-sand and
shale lithologies.
Seismic
attributes were of limited use. Maximum values of the
reflection strength attribute were judged to be indicative of the greatest acoustic
impedance contrast between shale and cleanest sand. Acoustic impedance traces extracted
through Constrained Sparse Spike Inversion modelling compared favorably with wireline
measured impedance at well locations. Map view distributions of clean sand were extracted
in each sub-unit by applying the impedance cut-offs established from crossplots. Combined
attribute and inversion analyses revealed two kinds of sand distribution in the basin:
small, isolated alluvial fans located in structural highs, feeding off the western
boundary faults; and large fan, channel and sheet sands deposited in the deeper regions
controlled by N-S oriented fault systems. The hydrocarbon potential of the basin depends
upon the connectivity of these two kinds of sand distributions and upon the presence of
stratigraphic traps, structural traps, and the effectiveness of shales as seals.
AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia