Fluvial Depositional Environments Research Articles

LITHOSTRATIGRAPHY OF THE LOWER EROMANGA BASIN SEQUENCE IN SOUTH WEST QUEENSLAND

Five fully-cored and wire-line logged stratigraphic bores have been drilled by the Queensland Department of Mines, relatively close to producing oil fields in the Eromanga Basin, south-west Queensland. Correlations between the stratigraphic bores and petroleum wells have established lithologic control in an area where lithostratigraphy is interpreted mainly from wire-line logs. The Eromanga Basin sequence below the Wallumbilla Formation has been investigated, and a uniform lithostratigraphic nomenclature has been applied; in the past, an inconsistent nomenclature system was applied in different petroleum wells.Accumulation of the Eromanga Basin sequence was initiated in the early Jurassic by major epeirogenic downwarping; in the investigation area the pre-Eromanga Basin surface consists mainly of rocks comprising the Thargomindah Shelf and the Cooper Basin. The lower Eromanga Basin sequence in the area onlaps the Thargomindah Shelf and thickens relatively uniformly to the north-west. The sequence comprises mainly Jurassic/Cretaceous terrestrial units in which vertical and lateral distribution is predominantly facies-controlled. These are uniformly overlain by the mainly paralic Cadna-owie Formation, signalling the initiation of a major Cretaceous transgression over the basin.The terrestrial sequence over most of the area comprises alternating coarser and finer-grained sedimentary rocks, reflecting major cyclical changes in the energy of the depositional environment. The Hutton Sandstone, Adori Sandstone and 'Namur Sandstone Member' of the Hooray Sandstone comprise mainly sandstone, and reflect high energy fluvial depositional environments. Lower energy fluvial and lacustrine conditions are reflected by the finer-grained sandstone, siltstone and mudstone of the Birkhead and Westbourne Formations, and 'Murta Member' of the Hooray Sandstone. Similar minor cycles are represented in the 'basal Jurassic' unit. The Algebuckina Sandstone, recognised only in the far south-west of the investigation area, comprises mainly fluvial sandstones.

Cretaceous angiosperm invasion of North America

Angiosperms appeared in the coastal plains of eastern North America during the latest Barremian or early Aptian, reaching California by the Albian, or perhaps as early as Aptian. In Alaska, however, they are found in sediments only as old as latest Albian. From their earliest Cretaceous appearance, and well into the Late Cretaceous, angiosperms were most abundant and diverse in coastal and fluvial depositional environments, conifers remaining dominant in well drained and inland soils. Extensive dispersal of pioneering, coastal angiosperms occurred at a time of extensive sea-level fluctuation and went hand in hand with their mid-Cretaceous diversification. The early successes of invading angiosperms can most easily be attributed to their ability to colonise disturbed sedimentary surfaces. It is unlikely that they were initially successful in high salinity or other unfavourable habitats, or that they could compete directly with pre-existing plants for nutrients, pollinators or other resources.

New stratigraphic, sedimentologic and structural data on the kerri-kerri formation, Bauchi and Borno States, Nigeria

The Kerri-Kerri Formation is composed of flat-lying to gently dipping basalconglomerate, grit, sandstone, siltstone and clay which unconformably overstep the Maastrichtian Fika Shale and Gombe Sandstone. Five stratigraphic sections (including the type section at Kadi) and six boreholes were studied. The formation attains a thickness of about 200 m at Duku. The heavy mineral suite includes rutile, zircon, kyanite, staurolite, limonite, tremolite, sillimanite, pyroxene, hornblende and tourmaline, which are indicative of derivation from the nearby basement complex and older sedimentary rocks. The rare basal conglomerates, well-bedded siltstones and the presence of shrinkage cracks, clay-supported grits, local channel sandstones and thin horizons of coal and carbonaceous clay suggest a typical fluvial, deltaic and marginal lacustrine environment of deposition. The presence of the pollens Spinizonocolpites baculatus and Monocolpites marginatus among others confirms a Paleocene age for the formation. The interpretation of the surface and subsurface data is consistent with anasymmetrical graben structure of the Kerri-Kerri basin. The western margin of the basin was fault-controlled and active during the deposition of sediments during the Early Tertiary.

Oil and Water Production in a Reservoir With Significant Capillary Transition Zone

Summary Analytical and numerical methods are used to investigate the mechanism of water production in a high-permeability sandstone reservoir that has a capillary transition zone height comparable to formation thickness. Production rates are well above those for transition-zone water production alone. Consequently all wells are affected production alone. Consequently all wells are affected by coning shortly after the start of production. It is found that water cut is largely insensitive to total fluid production rate for the same recovery. The depth of well penetration and the effect of radial capillary pressure gradients are shown to be of secondary importance pressure gradients are shown to be of secondary importance in these circumstances. The predictions are confirmed by the results of a long-term pilot production test. Introduction This paper considers the mechanism of water production in a highly permeable sandstone reservoir with a 22API [0.9-g/cm3] under saturated oil and a strong edge aquifer drive. The findings are drawn from a study recently performed on the M-1 Sand reservoir of the Fanny field, performed on the M-1 Sand reservoir of the Fanny field, which is located on the eastern flank of the Oriente basin in Ecuador. M-1 Sand belongs to the Napo formation of the Cretaceous Age and consists of moderately to poorly cemented quartzose sands of high permeability. Reservoir depth is approximately 7,700 ft [2347 m]. A characteristic feature of the reservoir is the wells' predisposition to develop substantial water cuts after predisposition to develop substantial water cuts after short periods of production. Attempts have been made in the past to reduce water production by squeeze cement jobs and recompletions. However, these operations have not been effective but for the very short term and consequently the study has concentrated on attempting to define the nature of fluid movement within the drainage area of the wells. Reservoir Description M-1 Sand shows lithological features characteristic of a fluvial channel depositional environment. These features are exemplified by the Induction Electrical Survey of Well 18-B-2 (Fig. 1), which shows a basal unit 45 to 55 ft [14 to 17 m] thick, overlain by a variable number of smaller units that are separated by shale breaks and tight streaks. These upper units are of poor quality and limited lateral continuity. In contrast the basal unit contains no correlatable shale breaks although thin shales were encountered in some wells and early completion practices attempted unsuccessfully to make use of them. Because of this early experience and the absence of correlation it has been concluded that such shale breaks are of limited lateral extent and do not contribute materially to the prevention of water-cone development. prevention of water-cone development. The basal unit contains more than 90% of the original oil in place, estimated at 48 × 10(6) STB [7.6 × 10(6) stocktank m3]. Currently all wells are completed in this unit, which has provided all production to date. The upper units have been neglected for the purposes of this paper. The structural configuration of the reservoir is a faulted asymmetrical anticline of low structural amplitude. Fig. 2 represents the structure on top of the basal sand unit and shows the intersection of the oil/water contact (OWC) with this surface, giving rise to a maximum oil column of 65 to 70 ft [20 to 21 m]. A comparison of sand thickness with oil column height indicates that the base of the sand is everywhere close to the OWC and that all wells have high basal water saturations. Pressure support is by edge aquifer influx, but with strong underrunning giving behavior characteristic of a bottom aquifer. Reservoir and Fluid Properties The basal unit is variable in quality but characterized by high porosity and permeability averaging 20 to 25% and 2 to 3 darcies, respectively. Figs. 3 and 4 are capillary-pressure and relative-permeability curves representative of the basal unit. These curves are typical of a sandstone that contains large, well-interconnected pores. Sands of this unit are generally poorly cemented and friable. No fractures are evident from either cores or logs. There is no evidence of any fracture-induced effects on pressure buildup data, which correspond to a single permeability intergranular system. Average oil and water fluid properties are presented in Table 1. The oil and water viscosities at reservoir conditions are 12 and 0.35 cp [12 and 0.35 mPas] respectively, which give a very unfavorable endpoint mobility ratio. The displacement of oil by the encroaching aquifer is thus an unstable displacement and the strong underrunning of water quickly results in high producing water cuts in the wells. JPT P. 1559

Palaeopedogenic features and their palaeoclimatological significance for the nevremont formation (Lower Givetian), the Northern Ardennes, Belgium

The lower member of the Nèvremont Formation is characterized by the frequent occurrence of pedogenic features, which suggest intermittent exposure of the fluvial depositional environment. The evidence for pedogenesis comprises horizons of calcite glaebules and nodular calcrete, haematite segregation, resulting in pronounced colour mottling, and the formation of palaeosolic root-horizons with root tubes, cutanic features, burrows and striotubules. Based upon the presence of these features, it is suggested that the climate was semiarid. The source area of the quartz-rich parent clastic sediment was presumably subjected to intensive chemical weathering, resulting in mature quartzose sediments, with illite and kaolinite as dominant clay minerals.

Evolution of fluvial sedimentation in the Buntsandstein (Lower Triassic) of the Eifel (Germany)

The continental redbeds of the Buntsandstein (Lower Triassic) in the western Eifel (Germany) are composed mainly of fluvial and aeolian sediments. The terrestrial sequence reflects an evolution of fluvial depositional environments. In the Basisbildungen at the beginning of Triassic sedimentation, alluvial fans and mudflows distally intertounged with sandy braided rivers in local depressions of the pre-Triassic continent surface. In the Trifels-Schichten, slow subsidence and rapid shifting of narrowly spaced channels in low-sinuosity, highly braided, multi-channel river systems often resulted in reworking of upper parts of cyclothems, thus piling up thick sequences of stacked bar deposits. In the Rehberg-Schichten, large flood-plains developed due to increasing spacing and sinuosity of the channels and decreasing braiding of the river systems. Faster subsidence favoured preservations of predominantly complete cyclothems ideally terminated by thin aeolian sands. In the Karlstal-Schichten, the climax of regional diversification of sedimentary environment matched the development of a large aeolian sand sea which was intersected by generally moderately braided rivers. Aeolian sands were deposited as barchanoid-type dunes and interdune sheet sands and intertongued with fluvial channel and topstratum deposits. At the top of the Middle Buntsandstein, the Violette Grenzzone marks a hiatus in evolution resulting in recurrent change in fluvial style. In the Usch-Schichten, coarse detritus accumulated in multi-channel, low-sinuosity, pebbly highly to moderately braided rivers. Rapid channel shifting and slow subsidence often led to erosion of topstratum deposits and palaeosols. In the Malbergweich-Schichten, increase of channel spacing and sinuosity was accompanied by increasing subsidence. Sandy moderately to weakly braided streams and occasionally also meandering rivers deposited cyclic alluvial sediments. At the beginning of the Kyllburg-Schichten, another minor recurrence interrupted the evolution. Channel braiding increased once more, and rapid channel shifting, accompanied by slower subsidence, led to widespread erosion of overbank fines. At the top of the Kyllburg-Schichten, sinuosity increased more and more, and sandy moderately to weakly braided rivers graded into meandering streams. In the Voltziensandstein, fluvial environment passed into a deltaic and/or tidal milieu in front or at the margin of the prograding Muschelkalk sea. Transgression of the shallow marine Muschelkalk terminated the terrestrial period of the Buntsandstein in the Eifel. Evolution of fluvial sedimentary environment thus led in the Middle Buntsandstein from local alluvial fans via pebbly highly braided rivers to sandy moderately braided streams and finally to an intertonguing of aeolian dunes and multi-channel rivers with regionally different degree of braiding. Tectonic activity in the source areas and climatic change, at the beginning of the Upper Buntsandstein, resulted in reversion to conditions existing in the inferior part of the Middle

Sedimentation in an Arid Macrotidal Alluvial River System: Ord River, Western Australia

In the Cambridge Gulf-Ord River region of Australia, an area that experiences a dry monsoonal climate and a high tidal range (5.9 m), a variety of tidal-plain and fluvial depositional environments were recognized. Near the coast, prograding shorelines are characterized by extensive mangrove successional sequences and scattered thin beach-ridge deposits. In the interfluve regions and farther inland along the coast, tidal-plain sedimentation has given rise to extensive flats that are bare of vegetation at approximately the high spring tide level. Evaporites, algal-layered silts and clays, and massive sandy deposits form the bulk of these tidal-flat sediments. Sinuous tidal channels, displaying low width/depth ratios and characterized by a progressive tide wave, are found throughout the coastal tidal-flat region. These channels migrate laterally, leaving preserved channel sand bodies isolated in tidal deposits. In the funnel-shaped channel of the Ord River, the major river in the region receiving freshwater runoff, the tide wave is symmetrical at the mouth but becomes deformed upstream owing to a high amplitude/depth ratio; thus the velocity of flood currents increasingly exceeds ebb velocities upstream and ebb flow increases in duration. In the upper portions of the tide-dominated river channel, the largest bedforms within the channel migrate upstream under the influence of dominant flood currents, choking the channel with sand deposits. Extensive channel migration and meandering are characteristic of this region of the channel. In addition, extensive overbank crevassing occurs, a process that forms the bulk of the fluvial deposition. In the lower Ord River, linear, elongate tidal ridges within and seaward of the channel form the major sand deposits of the delta. These environments and their distribution and geometrical relationships characterize arid, high-tidal-dominated river systems.

Development of a braided-fluvial facies model for the Devonian Battery Point Sandstone, Québec

Eight distinct facies have been defined in a 110 m thick section of the Lower Devonian Battery Point Sandstone near Gaspé, Québec. The first is a scoured surface overlain by massive sandstone with mudstone intraclasts. Facies A and B are trough cross-bedded sandstones, with poorly- and well-defined stratification, respectively. Facies C and D consist of large isolated, and smaller multiple, sets of planar cross-stratified sandstones, respectively. Facies E comprises large sandstone-filled scours, facies F comprises ripple cross stratified fine sandstones with interbedded mudstones, and facies G comprises sets of very low angle cross-stratified sandstones.The overall context of the Battery Point Sandstone, the presence of rootlets, and the abundance of trough and planar-tabular cross bedding, all suggest a generally fluvial environment of deposition. Analysis of the facies sequence and interpretation of the primary sedimentary structures suggest that channel development began by scouring, and deposition of an intraclast lag. Above this, the two trough cross bedded facies indicate unidirectional dune migration downchannel (vector mean direction 291°). The large planar tabular sets are associated with the trough cross bedded facies, but always show a large (almost 90°) paleoflow divergence, suggesting lateral movement of in-channel transverse bars. The smaller planar tabular sets occur higher topographically in the fluvial system, and the rippled silts and muds indicate vertical accretion. Because of the very high ratio of in-channel sandy facies to fine-grained vertical accretion facies, and because of the evidence of lateral migration of large in-channel bars, the Battery Point River appears to resemble modern braided systems more than meandering ones.

Petrographic comparison of the Taylor and Victoria Groups (Devonian to triassic) in South Victoria Land, Antarctica

Abstract Detailed petrography of the Taylor Group is compared with the Victoria Group. The mature quartz arenites and subordinate subarkoses of the Taylor Group contrast with the immature subarkoses, lithic arkoses, and sublitharenites of the younger Victoria Group. Mechanical analyses indicate a littoral to fluvial environment of deposition for the Taylor Group and a fluvial environment for the Victoria Group. There is a marked provenance change from granitic or older quartzose sediment sources at the base of the Lashly Formation (Victoria Group) wherte volcanic lithic fragments appear and laumontite occurs. The presence of brown oxidised chlorites, possibly resulting from in situ weathering, is common throughout the Beacon Supergroup.