Fluvial Depositional Environments Research Articles

Abstract: Applications of the Ultrasonic Borehole Imager in Braided Fluvial, Eolian and Deltaic Depositional Environments in the Triassic Reservoirs of the Hassi Berkine South (HBNS) Field, Algeria 

Abstract: Applications of the Ultrasonic Borehole Imager in Braided Fluvial, Eolian and Deltaic Depositional Environments in the Triassic Reservoirs of the Hassi Berkine South (HBNS) Field, Algeria 

Fluvial Depositional Environments in a Non-Marine Cratonic Basin: Stacking Pattern Architecture as a Response to Baselevel Changes  :ABSTRACT

Fluvial Depositional Environments in a Non-Marine Cratonic Basin: Stacking Pattern Architecture as a Response to Baselevel Changes  :ABSTRACT

Synthetic Stratigraphy with a Stochastic Diffusion Model of Fluvial Sedimentation

ABSTRACT Models of stratigraphic completeness and bed formation in fluvial depositional environments have most often assumed that successive depositional and erosional events deposit or erode amounts of sediment independently. This results in a random-walk model for the total amount of deposited sediment locally as a function of time. We consider an extension of the random-walk model of sedimentation in an alluvial plain in which deposition or erosion is concentrated in randomly avulsing channels and sediment transport is modeled by the diffusion equation (Culling's model). In contrast to the random-walk model, this model results in an anticorrelated sequence locally as a function of time, i.e., after an area has aggraded it has a higher elevation and a lower rate of future aggradation. In a p evious paper we analyzed the topography generated by the model and argued that porosity variations could be associated with topographic variations. The power spectrum S (the square of the coefficients in a Fourier series) of one-dimensional transects of topography and porosity horizontally and vertically in this model have a power-law dependence on wave number k: S(k) k-s, with values of s close to those observed. In this paper we show that the model deposits sediment with a rate depending on time interval as a power law with exponent -3/4, more consistent with observations than the random-walk model. The model produces an exponential bed-thickness distribution with a skew depen ent on the sedimentation rate of the basin in accordance with observations. We also examine the persistence in the series of bed thicknesses as a function of depth. For the stochastic diffusion model of sedimentation no persistence is observed. If the model fully characterizes the autocyclic dynamics in fluvial sedimentary basins, the lack of persistence in the synthetic bed sequences suggests that observed persistence and cyclicity in real bed-thickness sequences must be the result of allocyclic processes.

Heavy mineral suites in the Statfjord and Nansen Formations of the Brent Field, North Sea; a new tool for reservoir subdivision and correlation

Heavy mineral data provide an independent basis for subdivision and correlation of the Statfjord-Nansen reservoir sequence in the Brent Field, UK North Sea. Because of its continental fluvial depositional environment, this sequence lacks a well-defined biostratigraphically-based correlation framework. Detailed well correlations are difficult because of the heterolithic nature of the reservoir and the lack of chronostratigraphically significant markers. Three major heavy mineral zones and a number of subzones have been established. These can be confidently correlated in cored sections across the Brent Field. The correlations made using the heavy mineral scheme generally parallel the boundaries between reservoir units, giving confidence to the current reservoir zonation and indicating that it has a sound geological basis. However, the mineralogical zonation of a crestal, faulted well, 211/ 29-D44 (BD44), differs significantly from the reservoir zonation. This illustrates the difficulties inherent in establishing field-wide correlations without support of independent correlation schemes.

Middle Jurassic non-marine siliciclastic facies in southern central Saudi Arabia

Middle Jurassic deposits of Saudi Arabia show distinct lateral facies variation, where the carbonates in the north are replaced by siliciclastic rocks in the south. In southern central Saudi Arabia, the Middle Jurassic deposits are composed exclusively of siliciclastic rocks, mainly sandstone with minor shale and siltstone, and rare conglomerate. Five stratigraphical sections were measured and studied along the southern Tuwaiq escarpments, where these rocks are well-exposed. A fluvial depositional environment is proposed here for the Middle Jurassic rocks in southern central Saudi Arabia based on sedimentological and petrological evidence. Eight different lithofacies were recognized in these deposits and each is described and interpreted. Cyclic sedimentation is prominent in all the sections studied; the most frequent transition is from medium-coarse pebbly sand to fine sands/silts/muds indicating a transition from sand flat or channel bar deposition, in which the upper flow regime dominates, to overbank deposition, where the lower flow regime prevails. Sandy bedform and downstream-accretion macroforms are the most common fluvial architectural elements. A braided stream system is the most appropriate model for these rocks, but the geomorphology of the streams was not constant in either space or time. However, the streams were braided most of the time, especially in the vicinity of the upstream source area in the southern highlands, and they changed their morphology gradually northward to become more sinuous, but never reached the stage where they become true meandering rivers. The change in stream morphology affected the distribution of fluviual facies and resulted in the presence of a proximal fluvial facies dominating in the south and a distal facies prevailing in the north. The streams flowed from south to north with little or no contribution from east-flowing tributaries. At this time, the Central Arabian Arch was a negative, submerged structural feature subsiding under the accumulating shelf carbonate sediments, whereas the Hadramaut and Mukalla Arches were positive features controlling the sedimentation pattern in southern central Arabia. Although the Middle Jurassic rocks, both in the north and in the south, form a slightly diachronous, contiguous sedimentary body, they differ from each other significantly. Therefore, it is recommended here that the Middle Jurassic siliciclastic facies in southern central Saudi Arabia be separated from the Dhruma Formation and be recognized as a new stratigraphical unit with formational rank.

Shelf-Slope Break Sedimentation and Erosion During Deposition of the Claiborne Group in Colorado and Wharton Counties, Texas: ABSTRACT

ABSTRACT Geological and geophysical data over a 6,500 square kilometer area across Wharton and Colorado Counties, Texas, are utilized to understand sedimentary processes that occurred along the shelf-slope break of the Eocene Claiborne Group. Sedimentation models based on seismic profile data and well log data are critical to the oil and gas industry. It can be demonstrated that Claiborne deposition generally took place in middle neritic water depths on the shelf, however, some sediment did bypass the shelf and was deposited in deeper waters downdip. Sands of the Yegua Fm. were transported basinward from the deltaic and fluvial depositional environments in the updip area of Colorado County, bypassing shelf deposition. In general, there was little sedimentation taking place along the shelf except during short periods of transgression. Downdip at the shelf-edge, subsidence rates were higher and sedimentation became more aggradational. Possible drops in sea-level and/or changes in depocenter locations brought about downdip deposition of sediment beyond the shelf edge during most periods of Yegua-age deposition. It appears that even during low accumulation times on the shelf, sediment was being deposited downdip beyond the shelf-edge. Slumping along the over-steepened shelf margin was common during Claiborne deposition. The style of Claiborne age slumping was controlled by many factors including the placement of the Wilcox shelf. During high sedimentation times, erosion of the shelf margin from slump related carving appears to have taken place.

The Indicator Variogram and the Simple Kriging Estimator: Useful Tools to Complement Lithologic Correlation in a Complex Fluvial Depositional Environment: ABSTRACT

The Indicator Variogram and the Simple Kriging Estimator: Useful Tools to Complement Lithologic Correlation in a Complex Fluvial Depositional Environment: ABSTRACT

Synvulkanische Sedimentation in einem fluviatilen Ablagerungsraum: Das basale "Oberrotliegend" im permokarbonen Saar-Nahe-Becken

Synvulkanische Sedimentation in einem fluviatilen Ablagerungsraum: Das basale "Oberrotliegend" im permokarbonen Saar-Nahe-Becken

Compositional trends in the Permian sandstones from the Denison Trough, bowen basin, queensland reflect changing provenance and tectonics

Point-count data of sandstone samples collected from six sedimentary formations encountered in boreholes in the Permian sequence of the Denison Trough (an Australian backare/ retroarc foreland basin) provide information about the tectonic evolution of their source areas and the depositional sites. Plots of the detrital compositions of these Permian sandstones against borehole depths indicate that the Reids Dome Beds sandstones, containing highly abundant lithic/volcanolithic grains, mark the onset of intense compressional tectonics and arc volcanic activities to the east accompanied by extensional tectonics and subsidence in the trough. Folding and thrusting owing to intense compressional tectonics in the New England Fold Belt and Arc volcanism in the Camboon Volcanic Arc region to the east generated a great supply of recycled sediment and volcanic detritus that led to a rapid infilling of the subsiding Denison Trough during formation of the Reids Dome Beds sandstones in Early Permian time. The detrital composition of the sandstones of the overlying Cattle Creek Formation, Aldebaran Sandstone, and the Freitag Formation indicate gradually decreasing compressional tectonics and arc volcanism accompanied by increasingly dominant sediment-supply from the stable continental craton to the west. The Freitag Formation sandstone compositions mark the quietest tectonic and volcanic episode in the region, accompanied by subsidence of the Denison Trough owing to thermal cooling during the Middle Permian. The Peawaddy Formation and the Bandanna Formation sandstone compositions represent a Late Permian renewal of compressional tectonics and arc volcanism to the east accompanied by uplift and folding of the sedimentary strata, resulting in the formation of largely fluvial depositional environments in the Denison Trough. Modal compositions of the Bandanna Formation sandstones indicate that renewed arc volcanism and compressional tectonic activity attained maximum intensities during the Late Permian.

Recent and ancient fluvial deposition systems in the Amazonian foreland basin, Peru

AbstractStill active Sub-Andean foreland deformation is suggested to have syndepositionally modified the fluvial depositional environments in the Peruvian Amazonian foreland basin throughout Neogene-Quaternary time. Modern fluvial aggradation continues to proceed on a large scale (c. 120 000 km2) in two differing depositional systems. Firstly, various multistoried floodbasin deposits are derived from the meandering and anastomosing rivers within the subsiding intraforeland basins. Secondly, in the northern part of the Pastaza-Marañon basin the largest known Holocene alluvial fan-like formation (c. 60 000 km2) composed of reworked, volcaniclastic debris derived from active Ecuadorian volcanoes, has been identified.The widespread, poorly known, dissected surface alluvium (terra firme) which covers the main part of the Peruvian Amazonian foreland basin shows further evidence of long-term foreland deformation, and terraces indicate both the effects of tectonism and Pleistocene climatic oscillations. In northern Peru, the surface alluvium was deposited by a Tertiary fluvial system with palaeocurrents to the west and northwest into the Andean foreland basin. In southern Peru, the respective surficial alluvium was part of a post-Miocene fluvial system flowing northeast into the main Amazon basin. Both systems were gradually abandoned when the eastward migrating Andean foreland deformation led to the more distinctive partitioning of the intraforeland basins, and the modern drainage system was created.

A Two-Stage Stochastic Model Applied to a North Sea Reservoir

Summary We present a two-stage stochastic model that caters to the large-scalegeological heterogeneities resulting from different rock types and the inherentspatial variability of rock properties. The suggested approach combines severalelements from a variety of models, methods, and algorithms that have emergedduring the last few years. This twostage procedure can be used to generateseveral geologically sound realizations of a reservoir in an efficient manner. Stage 1 preserves the important geological architecture, while Stage 2 providessmall-scale variability in the rock properties. At both stages, the stochasticmodels are conditional on the actual values observed in wells. Hence, everyrealization honors the observations. An example from a highly heterogeneous North Sea reservoir, deposited in an upper shore-face environment illustratesapplication of the model. Introduction As a result of high costs in offshore areas like the North Sea, only aminimum of exploration and appraisal wells can be justified before importantfield development decisions are made. The use of oversimplified geologicalmodels based on data from a limited number of widely spaced wells is probablyone of the most important reasons probably one of the most important reasonsfor the failures in predicting field performance. Oversimplification and theuse of performance. Oversimplification and the use of unrealistic geologicalmodels partly results from the paucity of well data but also results from theinappropriate use of available data. Experience shows, for example, that linearinterpolation of petrophysical characteristics between wells some kilometersapart usually will not give a realistic image of the heterogeneity required topredict fluid flow. To give a realistic description of the point-to-pointvariation, we resort to point-to-point variation, we resort to stochasticmodels and simulation. A reservoir is intrinsically deterministic. It exists, and its propertiesand features are potentially measurable at all scales. A potentially measurableat all scales. A reservoir is the product of many complex processes(sedimentation, erosion, burial, processes (sedimentation, erosion, burial, compaction, diagenesis, etc.) that operate over millions of years. Why, then, do we have to apply stochastic modeling? Haldorsen and Damsleth list thefollowing reasons:the incomplete information about a reservoir'sdimensions, internal architecture, and its rock-property variability at allscales;the complex spatial disposition of reservoir building blocks orfacies;the difficult-to-capture rock-property variability and variabilitystructure with spatial position and direction;the unknown position anddirection;the unknown relationships between the property value and thevolume of rock used for averaging (the scale problem);the relativeabundance of static (point values along the well for kH, Sw, and seismicdata) over dynamic (time-dependent effects, how the rock architecture affects arecovery process, etc.) reservoir data; andconvenience and speed--handdrawing reservoir architectur and point-value realizations in three-dimensionsis a very difficult and time-consuming process. The phenomena or variables that we normally describe with stochastic modelsare those that influence the amount, position, accessibility, and flow offluids through reservoirs. Thus, stochastic modeling or simulation in thiscontext usually refers to the generation of synthetic geological architectureand/or property fields in one, two, or three dimensions. The differentrealizations are conditioned to observations and possess a number of otherdesirable reservoir/geological features that should provide an improved basisfor recovery predictions. In addition, the uncertainty and risk associated withdifferent development options can be quantified better Dubrule gives a very good review of stochastic models for reservoirdescription, while Weber and van Geuns discuss the problem from a geologist'spoint of view, problem from a geologist's point of view, including some of thepossible pitfalls. Several authors present valuable contributions to the theoryand applications of stochastic modeling within the petroleum industry. Two-Stage Model To mimic reality, heterogeneity must be accounted for because it is one ofthe most important factors governing fluid flow. A number of differentapproaches exist for the stochastic modeling of heterogeneities. The choice oftechnique depends on (1) the objective and scale of the study, (2) theavailable input data, (3) the theoretical skills of the people involved, and(4) the software available. The goal is to improve the evaluation of theproduction capacity of the field by introducing small- and/or large-scaleheterogeneities into the reservoir description. Discrete vs. Continuous Models. The distinction between two main classes ofstochastic models (discrete and continuous) is convenient. A finerclassification of the discrete models has been proposed. Discrete models weredeveloped to describe geological features of a discrete nature (e.g., locationsof sand in fluvial depositional environments or locations of shales suspendedin sands). JPT P. 402

Jurassic Sequence Stratigraphy of the Eastern Gulf Coastal Plain: Applications to Hydrocarbon Exploration

Based on regional stratigraphic and sedimentologic data, three unconformity-bounded depositional sequences associated with cycles of relative sea-level change and coastal onlap are recognized for Jurassic strata in the eastern Gulf Coastal Plain area. These sequences are designated, in ascending order, the LZAGC (Lower Zuni A Gulf Coast)-3.1, the LZAGC-4.1, and the LZAGC-4.2 sequences and include Callovian through Kimmeridgian Stage strata. An understanding of the relationship of Jurassic reservoirs to sequence stratigraphy can serve as an aid to hydrocarbon exploration in the eastern gulf area. The most extensive and productive Jurassic hydrocarbon reservoirs in the study area occur within the progradational, regressive highstand deposits of the LZAGC-3.1 and LZAGC-4.1 depositional sequences. For example, the majority of Norphlet sandstone reservoirs in the onshore and offshore Alabama area are interpreted to have accumulated in eolian dune, interdune, and wadi (fluvial) depositional environments, which occurred in association with the highstand regressive system of the LZAGC-3.1 sequence. The most important Smackover reservoirs generally consist of partially to completely dolomitized ooid and peloid packstones and grainstones in the upper portion of the unit. These reservoirs occur in subtidal to supratidal, shoaling-upward carbonate mudstone to grainstone cycles in the highstand regressive system of the LZAGC-4.1 sequence. Inmore » addition, minor reservoirs that are discontinuous and not well developed are associated with the shelf margin and transgressive systems of the LZAGC-4.1.« less

Lithological Discrimination and Correlation in Oil Sands Using Rock Magnetic Properties

The Lower Cretaceous McMurray Formation, which contains most of the bitumen reserves of the Athabasca oil sands, comprises uncemented quartz sands with siltstone, shale, and local ironstones. The sequential fluvial, estuarine, and marine depositional environments of the McMurray drainage basin have resulted in the complex juxtaposition of differing lithofacies. Horizontal continuity of lithofacies is limited. Sand body geometries are many and varied. Prediction of sand body geometry has important economic applications; a strong positive correlation exists between sand facies and oil grade. An investigation of the magnetic property variations in specimens from five closely adjacent boreholes within the McMurray Formation has shown that it is possible to: (1) document objective magnetic property parameters to differentiate distinct lithological units; (2) use these same magnetic parameters to establish between borehole lithostratigraphic correlations; and (3) to show that the magnitude of some magnetic parameters bears a direct relationship to the oil content of a lithology.

Detailed Mapping of Fluvial Sand Bodies Improves Perforating Strategy at Kern River Field

The producing sands of the Kern River field were deposited by the ancestral Kern River as a series of stacked, and often interconnected, sand bodies. Individual channel sands combine to create composite sand bodies that range from 5 to 100 ft in thickness and from 100 ft to as much as several miles in lateral extent. This high degree of variability in both the thickness and areal extent of the oil-bearing sands inevitably produces sands not conductive to orderly and predictable, steam displacement. These sand bodies, which alone are not capable of physically or economically supporting a steamflood, may be overlooked or inefficiently perforated. However, careful planning allows for these sands to be more fully exploited when the conditions for natural gravity drainage are optimum. In the Kern River field, this means taking advantage of oil viscosity reductions (preheating) realized when the underlying sand is being actively steamflooded. In addition to the importance of timing, detailed geologic reconstructions of individual sand channels are essential to enable selective perforating of those producers which are best able to effectively produce the sand body. An efficient and timely production program under these conditions demands a high degree of communication between the geologist andmore » the engineer, and insures maximum productivity from sands deposited in a complex fluvial depositional environment. A field study is included.« less

Sedimentology of miospores in the Middle to Upper Devonian Oneonta Formation, Catskill Magnafacies, New York

Studies of miospores in the siltstones of various fluvial depositional environments in the Catskill magnafacies have demonstrated a strong correlation between environment and miospore concentration. Most overbank samples are barren, whereas channel bar samples are usually productive of spores. The concentration is lower than in Cenozoic samples of similar origin: about 5000/g maximum. Channel fill samples are another order of magnitude lower: 700/g maximum. Non-red shales, siltstones and silty sandstones contain spores, while red rocks are regularly barren. However, studies of samples collected for palynology on field determination of silt content and non-red color show no “fine tuned” correlation between spore-content and either (1) grain-size as measured in thin section, or (2) ferric/ferrous iron ratios (as a measure of oxidation-level, either at the time of deposition or later).

Enhancing Geological Description of a Naturally Fractured Reservoir via Drawdown Testing: ABSTRACT

The Pecos Slope Abo gas field is located on the northwestern edge of the Northwestern shelf of the Permian basin. The 600-mi{sup 2} field was designated a tight gas formation during 1981 and 1982, which resulted in approximately 800 wells drilled through 1988. The tight gas designation required documenting core, production, and transient pressure test information. Pressure was equal throughout the reservoir, which resulted in normal hydrostatic reservoir pressure on the west side. However, the east side of the reservoir, which is 2,000 ft downdip, is under-pressured. A review of this information suggests that this formation, with lenticular sands, is a naturally fractured reservoir. Internal reservoir geometry, best described by the depositional environment, determines recovery efficiency. for example, the wave-dominated Woodbine Formation of the East Texas field has a very high recovery efficiency. In contrast, complex geometries such as fluvial-dominated deltaic reservoirs have lower recoveries due to poor facies continuity. The lenticular Pecos Slope Abo formation falls in the fluvial category or depositional environments. The Pecos Slope Abo gas field has been producing for six years. During this time, daily production rates and flowing wellhead pressures have been recorded for more than 200 wells (half million data points). This productionmore » information was treated as a long-term pressure drawdown test and was analyzed using a naturally fractured reservoir analytical technique. The descriptors resulting from the analyses are correlated with performance to arrive at an enhanced characterization of the internal reservoir geometry which will be useful when evaluating infill drilling opportunities.« less

Reservoir Description From Seismic Lithologic Parameter Estimation

Modern three-dimensional (3D) seismic data assist not only in delineating reservoir geometry, but also in predicting porosity and lithology variations away from well control. This case study of an oil-producing channel sand in the Taber/Turin area, Alta., Canada illustrates the improvement in reservoir characterization achieved with an integrated approach incorporating both well and seismic information.

Possible new constraints on late Miocene depositional patterns in west-central California

In the San Francisco Bay area, estuarine, lacustrine, and fluvial depositional environments existed contemporaneously within the Mulholland Formation, which was deposited in the Contra Costa basin from 7.7 to 6.5 Ma. The estuarine facies is differentiated from the nonmarine facies on the bases of ostracodes and sedimentology. Presence of the estuarine facies in the Mulholland Formation demonstrates that the Contra Costa basin was at sea level, the western part of the basin being a marine embayment for about 1 m.y. Absence of fresh Sierra Nevada-derived material in the lower Mulholland Formation indicates that a topographically elevated area existed east of the Contra Costa basin, effectively deflecting the Sierran debris, which is represented by the coeval Neroly Formation found in the eastern central Coast Ranges. To the west of the Contra Costa basin, some gaps in the Coast Ranges allowed connection with the Pacific Ocean.

Use of Inversion for Reservoir Delineation Within a Fluvial Depositional Environment, Eromanga Basin, Queensland, Australia: ABSTRACT

Reservoir delineation within fluvial deposits has been a source of concern and disappointment to both exploration and development groups. Seismic methods have greatly enhanced the ability to predict the location of reservoir units within clastic sequences. Conventional seismic processing and displays of data still fail to adequately define these subtle reservoirs in many cases. Within a complex stratigraphic sequence, detailed information concerning the nature and distribution of reservoir units can be obtained through reprocessing and inversion of seismic data. The reprocessing requires frequency enhancement, detailed velocity analyses, and phase adjustment (using well data as a standard). The inversion process involves quantification, calibration, and careful selection of display parameters. Some well information is essential for modeling and calibration. Color displays of the well data modeling are called Earthlogs. This paper will discuss the application of seismic data inversion and Earthlog models within the Jurassic clastic sequence located in the Eromanga basin, Queensland, Australia. One of the main reservoir units (Hutton formation) was deposited within a braided-stream depositional environment.

GEOLOGICAL CONTROLS ON RESERVOIR QUALITY OF THE NORTHERN PERTH BASIN

The major onshore Dongara gas field and a number of adjacent minor gas and oil pools are reservoired in basal Triassic sandstones that are sealed by the overlying Kockatea Shale. Reservoir quality is found to be controlled primarily by the local provenance of the sandstones, by diagenesis and the regional palaeotopography. Sandstones east of Dongara are reworked products of a Late Permian fan delta (Wagina Sandstone) that extended westwards from the basin's eastern, fault controlled margin. Localised high energy streams drained the palaeoslope, depositing thin wedges of mainly fluvial sediments upon and around the flanks of the Permian fan delta during a regional rise in sea level in the Early Triassic. Sandstones to the north of Dongara are localised, low energy offshore bars and strandline deposits derived from Precambrian of the Northampton Block. Diagenetic alterations of the Triassic sandstones, also controlled by the sandstones' provenance, have substantially reduced primary porosity and control permeability. The common presence of the authigenic clay mineral, dickite, is taken as evidence that a fluvial environment of deposition controlled formation of the reservoir rocks.