DETECTION OF RESERVOIR SANDS USING SEISMICATTRIBUTES AND SPECTRALDECOMPOSITION IN THE SOUTHEAST OF PATTANI BASIN, GULF OFTHAILAND

Abstract

Pattani basin is a structurally complex extensional basin of the Gulf of Thailand. The reservoirs are highly compart-mentalized sand by the rapid lateral and horizontal stratigraphic changes due to fluvial depositional systems (Lower to Middle Miocene) and a series of normal faults. The reservoirs in the study area are thin and limited in lateral extent which makes it difficult to predict reservoir distribution, orientation and thickness
based on conventional seismic volume. Advanced geophysical techniques were applied to improve the reservoir imaging and prediction. RMS and coherence attributes successfully detected the channel-like features by using twenty-milliseconds (20ms) window horizon slicing along the reservoir interval. Far angle stacked volume delivers different imaging of reservoir distribution for more lateral extension. From rock physic analysis, acoustic Pimpedance and near angle elastic impedance can discriminate sand and shale in unit 2 and 4. The far angle elastic impedance can help discriminate sands in unit 2, 3 and 4. High amplitudes on the root-mean square (RMS) amplitude attribute correspond to sands at well locations from blind test wells. Coherence provides higher resolution for detecting channel edges. The channel width varies from 150 to 950 meters and N-S to NW-SE orientation. Spectral decomposition shows a good response tuning at 36 Hz of 20 meters thick sand while higher frequencies show bright amplitudes for relatively thinner sand. This study suggests that the RMS and coherence can be used to detect reservoir distribution and spectral decomposi-tion can predict thickness