A review of clastic sandstone reservoirs in the Penyu Basin and Tenggol Arch area, adjacent to the south-western flank of the Malay Basin revealed that most deep reservoirs are affected by diagenetic alteration of reservoir mineral components. Furthermore, fluid inclusions in quartz are seen at distinct stratigraphic reservoir levels. These inclusions occur in Oligocene reservoirs in Groups L and M and in Miocene reservoirs of Groups K and H. However, to-date no oil inclusions have been found in Groups I and J. There appear to be two distinct populations of fluid inclusions in the so-called 'oil quartzes': (i) oil inclusions in allochthonous, detrital quartz grains. These inclusions are thought to be of the primary type, formed when oil was incorporated in growing quartz crystals, and oil is seen encapsulated in 'loose' quartz grains. There is no evidence of destructive diagenesis or cementation in these relatively shallow (Miocene) host reservoirs, and oil migration is not confirmed by other indicators such as bitumen, which is often found in deeper carrier beds together with oil quartzes. The origin of these oil quartzes is somewhat controversial, and cannot be determined with certainty. They were probably shed into the basin from eroded granitic basement horsts and ridges.(ii) in situ oil inclusions in quartz cement. The occurrence of oil encapsulated in quartz cement (secondary or tertiary inclusions) indicates oil migration had preceded quartz cementation. So-far, oil-bearing inclusions attributed to fractures could not be confirmed with certainty. Assuming a relatively constant temperature gradient in the basin during the Miocene, quartz cementation will have started at a palaeo-depth of ca. 2000 m or at 105 0 C, and porosity was mostly destroyed by a depth of ca. 3000 m and 130 0 C. Occasionally overpressures are observed. According to this model, oil had migrated into and percolated within reservoirs during the Miocene, but became locked in closed pores as quartz cement invaded pore spaces under increasing overburden and temperature. Consequently, fluid inclusions in quartz for this model suggest that depths of greater than 3000 m below mud line (BML) are likely to encounter sandstones with deteriorating reservoir properties in the study area.
TX 75083-3836, U.S.A., fax ϩ1-972-952-9435 SUMMARYReprocessing of vintage seismic data was conducted to address reservoir uncertainties in a fractured and karstified carbonate basement. The objectives were achieved by employing advanced processing technologies that included Full Waveform Inversion (FWI), TTI Reverse Time Migration (TTI TRM), Adaptive Curvelet Domain Multiple Separation (ACDS) and azimuthal anisotropic NMO.FWI is a data-fitting method designed to deliver high-quality, high-resolution velocity models critical for PSDM imaging. Currently, FWI concentrates on low frequency (3 -10Hz) transmitted energy (head waves and diving waves) as well as some reflection energy. The resulting FWI velocity model displayed very high resolution and good geological correlation. Forward modeling through the FWI technique generated synthetic shots that corresponded to the real seismic shots accurately.TTI RTM was applied to complement the high resolution FWI model and to achieve the best imaging around the target area where velocities were complex. Prior to the imaging Shallow Water Demultiple (SWD) and Surface Related Multiple Elimination (SRME), multiple separation was as critical to multiple prediction. A conventional Least Squares separation was applied in the 2D X-T domain. However, it was unsuccessful in separating crossing primaries and multiples with similar dips. Therefore, ACDS was appliedin the 4D curvelet domain and achieved successful representation of linear and curved events with sparse coefficients. Finally, azimuthal anisotropy was observed in the CDP gathers and in the crossline sections. Azimuthal anisotropic NMO based on a scanning method corrected this effect and aligned the data thoroughly.These technologies covered pre-migration processing, velocity modelling and migration. The combined application of these advanced technologies delivered significant improvement of the overall seismic quality, with reduced multiple contamination, sharper fault definitions, a crisper top basement and superiorfracture imaging within the basement.
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