Application of Acoustic Impedance Inversion to Evaluate the Pay Zone Distribution in Sepat Field, Malay Basin

The Sepat oil and gas field, in Malay Basin consists of thin hydrocarbon sands and some intercalated coal beds encased in shales which are often beyond seismic resolution. This poses a major challenge in delineation of prospect hydrocarbon sands of the reservoir. Therefore, this research applied post-stack inversion methods such as the Bandlimited and Model-based techniques on Sepat 3D seismic cube and well-logs data to generate impedance volumes linked to rock properties such as lithology, pore fluids, etc. The acoustic impedance data has improved resolution due to the contribution of very low frequencies from the well log data. Thus, the impedance volumes are purported and used (1) to discriminate and delineate low impedance gas-saturated reservoir sands from non-gas reservoir sands, and (2) to aid in interpreting correct subsurface lithology identification and fluid content distribution. In this study, the Hampson-Russell software package was used to build a high resolution acoustic impedance inversion models. The main steps in the procedure included calibration by tying well logs to the seismic data for determining the low frequency acoustic impedance trend, estimation of the wavelet, generation of a low-resolution background model, and inversion of the seismic trace.