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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