Pale Sandstone Research Articles

Geology of the Lower Triassic Jakabhegy Sandstone Formation, Hungary, SE Transdanubia

The Jakabhegy Sandstone Formation, known for a long time at surface in the western part of the Mecsek Mts, SE Transdanubia, was encountered by several boreholes in the second half of the 20th century in a large part of SE Transdanubia, during exploration for uranium ore in the Upper Permian formations in its subcrop. The formation is made up of five informal lithologic units, from the base upward the main conglomerate, the gravelly sandstone, the pale sandstone with conglomerate 2 at its base, then the red-brown siltstone and sandstone and at the top the variegated sandstone (units a, b, c, d, e). Grain size becomes finer upsection, the grains are medium-rounded, and sorting generally improves upward. Planar cross-bedding of varying size is characteristic. The Jakabhegy Sandstone Formation occurs in two types of development. In the case of complete development, all the lithologic units are present, but the lower two (a+b) do not overlap the Late Permian-Early Triassic Kővagoszőlős Sandston...

RESERVOIR QUALITY, DIAGENESIS AND SEDIMENTOLOGY OF THE PALE AND SUBU SANDSTONES: RE-VISITING THE EASTERN PAPUAN BASIN, PAPUA NEW GUINEA

Two shallow diamond drill holes (Subu–1 and Subu–2) continuously cored in August and September 2001 by InterOil Australia represent the first sub-surface penetrations of reservoir quality sandstones in the Eastern Papuan Basin of Papua New Guinea. These wells intersected two sedimentologically distinct thick quartz sandstones (>100 m). The upper sandstone unit is Campanian in age and is correlated with the Pale Sandstone, whereas the lower sandstone is of Turonian age and has not been reported previously, and is tentatively named as the Subu Sandstone in this paper.The core has been the subject of detailed reservoir quality and diagenetic study as part of a multi-disciplinary study conducted by CSIRO Petroleum. The results of the reservoir quality portion of this study form the basis of this report and demonstrate the following:There are two distinct depositional systems present with a lower sandy slope apron and basin floor fan system (Subu Sandstone) and a younger upper shoreface-shallow marine depositional system (Pale Sandstone).While the porosity and permeability data for subsurface samples (5 to 16% and 0.1 to 1000mD) are lower than previously reported by Boult and Carman (1990) for surface samples both the sandstone units demonstrate thick, good reservoir quality reservoir capable of holding significant volumes of hydrocarbons.Bitumen is present in the pore space through out the sandstones in both wells. The presence of biodegraded hydrocarbons demonstrates that liquid hydrocarbons have been generated in the basin and have either migrated through the Subu and Pale sandstone or have been reservoired in them.Associated with the bitumen is pyrite precipitated as an in-situ by-product of shallow biodegradation of the parent liquid hydrocarbon as indicated by sulphur isotope analysis.Diagenetic effects include compaction (the dominant control on reservoir quality), minor quartz cementation, minor secondary porosity generation, and in thin zones localised carbonate cementation.Despite their very different depositional settings and age difference the thin section petrology of the Pale and Subu sandstones are very similar. The subtle difference between them is textural (grain size, sorting) and detrital clay content. The Subu Sandstone is typically finer grained, displays a higher degree of sorting and has a higher detrital clay content than the Pale Sandstone.The character of these sandstones may have as much to do with provenance as with depositional environment and may indicate a separate quartz-rich depositional system sourcing sediment from the Australian craton independent of the Fly Platform Toro/Imburu systems.

Britannia Field, UK North Sea: petrographic constraints on Lower Cretaceous provenance, facies and the origin of slurry-flow deposits

Deep-water sandstones of the Early Cretaceous Britannia reservoir are rich in ‘muddy’ material, with the development of unusual ‘slurry-flow’ deposits ( sensu Lowe & Guy 2000 ), including banded facies. The banding comprises couplets of pale sandstone containing microporous detrital chlorite and other clays, retaining substantial porosity, and dark sandstone in which biotite (now altered to chlorite) has promoted quartz pressure solution that has largely destroyed porosity. The main source of the abundant chlorite and biotite is the Jurassic Forties Igneous Province, underlying and surrounding the Britannia Field. Altered alkali basalts and other lithologies here are known to be rich in both minerals. Grain-size distributions have been examined using image analysis. The banded facies are generally finer grained than the high-density turbidite and unbanded slurry-flow sandstones, and may be a distal equivalent. Dark bands in some cases contain no more fine clays than associated light bands, indicating that Lowe & Guy’s model for dark-band formation, invoking a cohesive sublayer, is incomplete. Gelation of chlorite-rich clays within each banded couplet is proposed as an alternative mechanism. These microporous pore-filling chlorites have restricted the precipitation of quartz overgrowths and other non-porous cements, although their presence inhibits permeability.

A review of the petroleum potential of Papua New Guinea with a focus on the eastern Papuan Basin and the Pale Sandstone as a potential reservoir fairway

Abstract Substantial oil seeps were first reported from the eastern Papuan Basin in 1911, and oil has since been produced from the sub-surface, but not in commercial quantities. A significant discovery of gas in 1986 sparked an upsurge of activity within the adjacent western Papuan Basin. From 1986 to 1992, 13 new hydrocarbon discoveries were made, which included four major oil fields, and an oil pipeline for export purposes was then opened in 1992. This activity did not spread to the eastern Papuan Basin due to a perceived lack of good reservoir and the last well drilled there was over 30 years ago. In 1986, a potentially excellent reservoir, the Pale (Pah leh) Sandstone was discovered in outcrop in the eastern Papuan Basin. Thus the Papuan Basin as a whole remains an extremely prospective basin. However, due to high infrastructure costs most activity has recently been focussed on the already proven reservoir potential of the Late Jurassic Imburu and Toro Formations in the western section. The extent of the Imburu-Toro Formation reservoir in the western section of the Papuan Basin is well documented. It was deposited as several regressive episodes within an overall transgressive, passive-margin, clastic sequence. In the eastern section, the Late Cretaceous Pale Sandstone was deposited in a barrier island or strand-plain environment. Lateral equivalents of the Pale Sandstone and the potential for a new reservoir fairway have been documented for a strike length of approximately 400 km. This fairway is coincident with the northeast edge of the western Papuan Basin and on the northern edge of the Aure and Port Moresby Troughs of the eastern Papuan Basin. All the commercial oil accumulations and seeps found in the Papuan Basin before 1992 have been attributed to the Jurassic, with peak generation occurring in the Late Cretaceous prior to the formation of existing structures. In 1992 an oil seep was discovered which is geochemically very different to all the other oils found in the Papuan Basin. This was found to the north and east of the present discoveries that occur within the western Papuan Basin. The oil seep is indicative of undiscovered Tertiary source rock, which is currently at or near peak generation. However, most of this source rock in the north may be covered by overthrusted allochthonous terrain. The Aure Trough was a Late Cretaceous to Tertiary rift basin that later developed into an Oligocene to Mid-Miocene foreland basin depocentre occurring on the northern and eastern margin of the Papuan Basin. It is proposed in this paper that mature Tertiary source rocks which occur within this foreland basin and the Pale Sandstone reservoir may form a significant petroleum system on the northeastern rim of the western Papuan Basin and within the eastern Papuan Basin.