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The Betty field is a moderate-sized oil field situated in the Baram Delta Province, offshore Sarawak. The field displays many of the characteristics that are typical of this Tertiary deltaic province, notably: (1) the structure is a result of the interaction of delta-related growth faulting and later Pliocene compressional folding, (2) the reservoirs comprise Miocene shallow marine sandstones and shales, which accumulated during repeated phases of small-scale progadation and retrogradation within a major regressive clastic wedge (comprising the wave-dominated palaeo-Baram Delta), and (3) the hydrocarbons occur in numerous vertically-stacked sands separated by sealing shales and trapped by a combination of fault seal and dip closure. This paper discusses these aspects of the Betty field in more detail, particularly the nature and origin of the reservoirs, and relates this geological framework to the field's development and production performance. Structurally the field is relatively simple, consisting of a NE-SW trending anticline which is bounded to the south by a major E-W trending growth fault (Betty Growth Fault). The anticline is a result of rollover associated with growth faulting combined with Pliocene compressional folding along the NE-SW trending Baronia-Betty-Bokor anticlinal trend. The Betty reservoirs occur within a ca. 2450 ft (7 4 7 m) thick sequence (between 7200-9650 ft I 2195-2941 m sub-sea) of Late Miocene, Upper Cycle V clastic sediments, which accumulated in a wave-/storm-dominated, inner neritic to nearshore/coastal environment within the palaeo-Baram Delta complex. The sand bodies are mainly characterized by numerous, composite and/ or amplified coarsening upward/progradational sequences (ca. 160 ft I 49 m thick) overlain by generally thinner, fining upwardlretrogradationalsequences (ca. 20-50 ft I 6-15 m thick). The sand bodies are vertically heterogeneous but display high lateral continuity with excellent field-wide correlation, which is consistent with the inferred high wave-energy depositional setting. Vertical heterogeneity is reflected in variations in the thickness and frequency of shale layers, and in the distribution of four distinctive reservoir facies of varying rock quality: (1) poorly stratified sandstone (porosity ca. 23%; permeability ca. 1200 mD), (2) bioturbated sandstone (22%; 500 mD), (3) laminated sandstone (19%; 90 mD), and (4) bioturbated heterolithic sandstone (17%; 50 mD).

Three main rock types are found in the Rompin-Endau area. These are volcanics, igneous intrusives and sedimentary sequences. Metamorphic rocks occur only at Gunung I.esong. The volcanic rocks are referred to as the Jasin volcanics and represent the oldest rocks of the area, prollably of Mid-Permian to Triassic age. Some of these rhyolites are also mylonitised. A granite batholith found on the western flank of the area can be termed a biotite-adamellite granite. This granite pluton which has intruded the volcanic rocks, is similar to those found in other parts of the mu Endau area and has been dated to be of Late Triassic Age.On the eastern plateau, sedimentary sequences of sandstone, shale, siltstone and mudstone overly the volcanics. A similar sequence of sediment is seen capping the granite hill 1448 on the western side, forming a mesa. These sediments are referred to as the Tebak Formation which is of continental origin and exhibits subhorizontal dips. Plant fossils were recorded from light grey mudstone beds in the tributaries of Sungai Telentang, and a boulder of silicified wood was found in Sungai Anak Seladang on the western flank of Sungai Kinchin. The plant fossil has been identified as Frenelopsis malaina Ko'ono, which is a foliage of a conifer plant, giving an age of Upper Jurassic -Lower Cretaceous. The silicified wood is also that of a conifer plant Araucarioxylon telentangensis Idris with a minimum age Late Triassic. A major fault trending 345-350· runs along Sungai Kinchin.

Series of linear, steep noise have frequently been observed on post-stack marine data. Such aliased noise is closely associated with data acquired with large shot spacings, in our case mostly 3D data acquired with multiple sources and streamers. In many cases, the noise has been observed to penetrate the objective area of seismic sections and cause significant deterioration of the primary reflections. This paper reports on results of recent studies which have demonstrated that such noise is caused by aliasing of multiples. Some solutions are proposed.