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This study presents a classification for subaqueous clay‐laden sediment gravity flows. A series of laboratory flume experiments were performed using 9%, 15%, and 21% sediment mixture concentrations composed of sand, silt, clay, and tap water, on varying bed slopes of 6°, 8°, and 9.5°, and with discharge rates of 10 and 15 m3/hr. In addition to the characteristics of the boundary and plug layers, which have been previously used for the classification of open‐channel clay‐laden flows, the newly presented classification also incorporates the treatment of the free shear layer. The flow states within the boundary and free shear layers were established using calculation of the inner variable, self‐similarity considerations, and the magnitude of the apparent viscosity. Based on the experimental observations four flow types were recognized: (1) a clay‐rich plug flow with a laminar free shear layer, a plug layer, and a laminar boundary layer, (2) a top transitional plug flow containing a turbulent free shear layer, a plug layer, and a laminar boundary layer, (3) a transitional turbidity current with a turbulent free shear layer, no plug layer, and a laminar boundary layer, and (4) a fully turbulent turbidity current. A connection between the emplaced deposits and the relevant flow types is drawn and it is shown that a Froude number, two Reynolds numbers, and a dimensionless yield stress parameter are sufficient to associate an experimental flow type with a natural large‐scale density flow. Deposits of submarine density flows can be important hydrocarbon reservoirs. Quality of these reservoirs is primarily controlled by grain size and clay concentration of the sediment mixture at the time of deposition. These parameters are dictated by the structures of the sediment carrying flow at the time of deposition. This study proposes a classification for muddy subaqueous density flows based on the flow structures. According to this classification a clay‐rich flow may fall within one of four distinct flow types: (1) a cohesive plug flow with laminar free shear and boundary layers and a plug, (2) a top transitional plug flow containing a turbulent free shear layer, a plug layer, and a laminar boundary layer, (3) a transitional turbidity current with a turbulent free shear layer and a laminar boundary layer, and (4) a turbulent turbidity current. A connection between the emplaced deposit and the relevant flow type is drawn through the results obtained from flume experiments. It is proposed that a Froude number, a boundary layer Reynolds numbers, a free shear layer Reynolds number, and a dimensionless yield stress parameter are sufficient to connect a flow type with a natural large‐scale density flow. Four distinct flow structures for muddy density flows were observedDependence of the deposit emplaced by a subaqueous density flow on its flow structure was examinedUpscaling of small flume experiments to large-scale natural density flows was investigated

The morphological evolution of submarine channel systems can be documented using high-resolution three-dimensional seismic data sets. However, these studies provide limited information on the distribution of sedimentary facies within channel fills, channelscale stacking patterns, or the detailed stratigraphic relationship with adjacent levee-overbank deposits. Seismic-scale outcrops of unit C2 in the Permian Fort Brown Formation, Karoo Basin, South Africa, on two subparallel fold limbs comprise thin-bedded successions, interpreted as external levee deposits, which are adjacent to channel complexes, with constituent channels filled with thick-bedded structureless sandstones, thinner-bedded channel margin facies, and internal levee deposits. Research boreholes intersect all these deposits, to link sedimentary facies and channel stacking patterns identified in core and on image logs and detailed outcrop correlation panels. Key characteristics, including depth of erosion, stacking patterns, and cross-cutting relationships, have been constrained, allowing paleogeographic reconstruction of six channel complexes in a 36-km² (14-mi²) area. The system evolved from an early, deeply incised channel complex, through a series of external levee-confined and laterally stepping channel complexes culminating in an aggradational channel complex confined by both internal and external levees. Down-dip divergence of six channel complexes from the same location suggests the presence of a unique example of an exhumed deep-water avulsion node. Down-dip, external levees are supplied by flows that escaped from channel complexes of different ages and spatial positions and are partly confined and share affinities with internal levee successions. The absence of frontal lobes suggests that the channels remained in sand bypass mode immediately after avulsion. [ABSTRACT FROM AUTHOR]

The Río Colorado meandering river system feeds the Salar de Uyuni, the World's largest salt pan in the southern Altiplano plateau (Bolivia). It is characterized by ephemerality due to the high aridity of the region, and a downstream decrease of river bankfull width and depth in the river terminus. Dryland meandering river systems in high-altitude regions have rarely been reported. We investigated the active processes in this system from the alluvial fan to the lower coastal plain. On-site surveys combined with high-precision GPS and high-resolution satellite imagery show that Río Colorado area is typified by generally fine sediment and a low gradient in the coastal plain. In the alluvial fan, where channel meandering is weak but still recognizable, the deposits are characterized by fining-upward sequences with gravel-prone sediments at the bottom, paleosols in the middle and clay-dominated sediments at the top. In the coastal plain the channel deposits consist of coarse to fine sand with sparse basal gravel, while the river banks and thus much of the floodplain consist of clay and silt in the upper coastal plain and very fine sand, silt and clay with salt deposits in the lower coastal plain. Grain-size distribution analysis show a linear decrease in bed load sediments downstream and a concurrent increase in suspended load sediments. These longitudinal variations in the proportions of sediment load are found to be consistent with changes in the topographic slope. The river gradient shows six intervals with downstream decreasing but internally quite constant slopes and sediment composition. Characteristic geomorphologic features are found to be head-cutting channels, chute channels, avulsions and crevasse splays. They illustrate the processes of erosion and deposition in this low-gradient river system and help understand sediment dispersal and their preservation potentials.

Analog outcrops are commonly used to develop predictive reservoir models and provide quantitative parameters that describe the architecture and facies distribution of sedimentary deposits at a sub seismic scale, all of which aids exploration and production strategies. The focus of this study is to create a detailed geological model that contains realistic reservoir parameters and to apply nonlinear acoustic full-waveform prestack seismic inversion to this model to investigate whether this information can be recovered and to examine which geological features can be resolved by this process. Outcrop data from the fluviodeltaic sequence of the Book Cliffs [Utah) are used for the geological and petrophysical two-dimensional model. Eight depositional environments are populated widi average petrophysical reservoir properties adopted from a North Sea field. These units are termed lithotypes here. Synthetic acoustic prestack seismic data are then generated with the help of an algorithm that includes all internal multiples and transmission effects. A nonlinear acoustic full-waveform inversion is then applied to the synthetic data, and two media parameters, compressibility (inversely related to the square of the com-pressional wave velocity vp) and bulk density, p, are recovered at a resolution higher than the shortest wavelength in the data. This is possible because the inversion exploits the nonlinear nature of the relationship between the recorded data and the medium contrast properties. In conventional linear inversion, these details remain masked by the noise caused by the nonlinear effects in the data. Random noise added to the data is rejected by the nonlinear inversion, contributing to improved spatial resolution. The results show that the eight lithotypes can be successfully recovered at a subseismic scale and with a low degree of processing artifacts. This technique can provide a useful basis for more accurate reservoir modeling and field development planning, allowing targeting of smaller reservoir units such as distributary channels and lower shoreface sands. [ABSTRACT FROM AUTHOR]

The texture of digital rock images, as recorded, for instance, with borehole imaging devices, is shown to reflect different bedding types. Textural segmentation of borehole images, therefore, subdivides the recorded sequence into bedding units. We show that a textural segmentation algorithm based on the concept of “texture energy” achieves good results when compared with synthetic as well as real data in which petroleum geologists have performed zonations on cores. Texture energy involves filtering of the original image with a set of texture sensitive masks. The filtering is done as a finite convolution over the size of the masks. On the resulting images the variance is computed over a relatively large sliding window, which, in its practical implementation, covers the full width of the image. The resulting nine one-dimensional curves are then clustered hierarchically into a user-determined number of image texture or lithological bedding classes. Principal component analysis previous to clustering can be used to reduce redundancy in the data. A recurring and relatively ill-defined problem in this field are macro-textures, i.e., the cyclic interbedding of two or more bedding types. We show that sliding Fourier transforms and variable mask scale can successfully address the zonation of macro-textures. In general, the method gives best results with mask sizes equivalent to 2–4 centimeters, reflecting the length scale at which the investigated geological bedding seems to have its highest variation.