Publications

A seismic reflection with an anomalous low frequency character has been mapped in the lbul Field area of South Sumatra, The mapped configuration of this anonialous reflection forms a linear pattern, and portions of this anonialy coincide with point bar sands as determined froni. core md log data. Recent drilling on this seisnuc anomaly has produced oil from several wells located off-structure and below the lbul Field oil-water contact.Seismic modeling of this anomaly was, carried out in an attempt to understand its significance. A personal computer with a memory capacity of 2000 bytes wits used for this niodel study.Synthetic seismograms were first generated. From the initial work it. was apparent that to properly estimate the composition of theseismic trace it was necessary to estimate the wavelet as closely as possible. Misleading conclusions are frequently the result when an assumed wavelet is used in synthetic seismogram work.The wavelet was estimated from the seismic trace and well logs using Fourier Transforms of the time doniin acoustic impedance, and the seismic trace. The conclusion of the synttieticseisnio~ransi tudy was that the low frequency anomaly is the result of a strong second cyle reflection from the overlying Basal Telisa Liwstone interfering with reflections generated froni stacked point bars in the uppcr part of the Talang Akar. Synthetic seismograms were generated froni a simple geological model composed of a flat, massive limestone overlying a simple sand wedge. Comparisons weie made between the wedge model and the stacked seisniic data to predict sand thicknesses.At the lbul-46 location, 75 feet of point bar sands were predicted, and after the well was drilled the log showed two sands (net thickness of 58 feet) seperated by 20 feet of shale. The upper sand contains hydrocarbons.