Quantitative textural analysis of sedimentary grains and basin subsidence modelling

Part 1: Quantitative textural analysis Shape analysis can provide important information regarding the origin, transport and deposition history of grains. Particle shape measurement has been an active area of research for sedimentologists since the 20th century. However, there is a lack of standardised methodology for quantitative characterisation of grain shapes. The main objective of this work is to develop methodologies that can be used by sedimentologists for quantitative textural analysis of grains such that the results obtained are comparable. A modular suite of code written in the Mathematica environment for the quantitative characterisation of sedimentary grains in 2- dimensions is presented. This image analysis package can be used to analyse consolidated as well as loose sediment samples. Using newly implemented image analysis methods, 20 loose sediment samples from four known depositional environments (beach, aeolian, glacial and fluvial) were analysed. This research aims to identify the most useful shape parameters for textural characterisation of populations of grains and determine the relative importance of the parameters. A key aspect of this study is to determine whether, in a particular sedimentary environment, textural maturity of the samples can be ranked based on their grain shape data. Furthermore, discrimination of sedimentary depositional environments is explored on the basis of grain shape. The available shape parameters suffer from a common shortcoming that particles, which are visually distinct, are not differentiated. To address this issue, the Inverse Radius of Curvature (IRC) plot which can be used to identify corners and measure their sharpness is introduced. Using the IRC plot, four shape parameters are proposed: number of corners, cumulative angularity, sharpest corner and straight fraction. This methodology is applied to a 4000 sand grain dataset. The textural analysis software package developed here allow users to quantitatively characterise large set of grains with a fast, cheap and robust methodology. This study indicate that textural maturity is readily categorised using automated grain shape parameter analysis. However, it is not possible to absolutely discriminate between different depositional environments on the basis of shape parameters alone. The four new shape parameters proposed here based on the IRC plot can be collectively used to quantitatively describe grains shape which correlates closely with visual perceptions. This work opens up the possibility of using detailed quantitative textural dataset of sediment grains along with other standard analyses (mineralogy, bulk composition, isotopic analysis, etc) for diverse sedimentary studies. Part 2: Basin modelling Subsidence modelling is an important part of basin analysis to better understand the tectonic evolution of sedimentary basins. The McKenzie model has been widely applied for subsidence modelling and stretching factor estimation for sedimentary basins formed in an extensional tectonic environment. In this contribution, a numerical model is presented that takes into account the effect of sedimentary cover on stretching factor estimation. Subsidence modelling requires values of physical parameters (crustal thickness, lithospheric thickness, stretching factor, etc.) which may not be always available. With a given subsidence history of a basin estimated using a stratigraphic backstripping method, these parameters can be estimated by quantitatively comparing the known subsidence curve with modelled subsidence curves. In this contribution, a method to compare known and modelled subsidence curves is presented aiming to constrain valid combinations of stretching factor, crustal thickness and lithospheric thickness of a basin. The parameter fitting method presented here is first applied to synthetically generated subsidence curves. Next, a case study using a known subsidence curve from the Campos Basin, offshore Brazil is considered. The range of stretching factors estimated for the Campos basin from this study is in accordance with previous work, with an additional estimate of corresponding lithospheric thickness. This study provides insights into the dependence of subsidence modelling methods on assumptions about input parameters as well as allowing for the estimation of valid combinations of physical lithospheric parameters, where the subsidence history is known

Innovation Of Petrophysical And Geomechanical Experiment Methodologies: The Application Of 3D Printing Technology

The petrophysical and geomechanical properties of rocks link the geology origin with engineering practice, which serves as the fundamental of various disciplinaries associated with subsurface porous media, including civil engineering, underground water, geological exploration, and petroleum engineering. The research methodologies can be mainly divided into three aspects: theoretical modelling, numerical simulation, and experiments, in which the last approach plays a critical role that can support, validate, calibrate, or even refute a hypothesis. Only replying on repeatable trials and consolidate analysis of precise results can the experiments be successful and convincing, though uncertainties, due to multiple factors, need to be scrutinized and controlled. The challenges also existed in the characterization and measurements of rock properties as a result of heterogeneity and anisotropy as well as the inevitable impact of experimental operation. 3D printing, a cutting-edge technology, was introduced and utilized in the study that is supposed to be capable of controlling the mineralogy, microstructure, physical properties of physical rock replicas and further benefit the petrophysical and geomechanical experimental methodologies. My PhD research project attempted to answer the questions from the standpoint of petrophysicisits and geomechanics scientist: Can 3D printed rocks replicate natural rocks in terms of microstructure, petrophysical and geomechanical properties? If not, by any means can we improve the quality of replicas to mimic the common rock types? Which 3D printing method is best suitable for our research purposes? How could it be applied in the conventional experiments and integrated with theoretical calculation or numerical simulation? Three main types of printing materials and techniques (gypsum, silica sand, resin) were characterized first individually, which demonstrated varying microstructure, anisotropy, petrophysical and geomechanical properties. Post-processing effect was examined on the 3D printed gypsum rocks that show impact differences on nanoscale and microscale pore structures. Through comparison, resin, the material used in stereolithography technology, best suits the reconstruction of intricate pore network that aims to complement digital rock physics and ultimately be applied in petrophysical research. Gypsum material, however, has been proved as the best candidate for geomechanical research spanning from reference samples to upscaling methods validation. Currently, a practical approach of utilizing 3D printing in petroleum geoscience is taking advantages of the characteristics we focus on the research while disregarding the other properties, by which a suitable 3D printing material and technique can emerge

THE FORMATION OF SMALL-SCALE GLACIAL FLUTES: A CASE STUDY OF THE CASTLE CREEK FOREFIELD, CARIBOO MOUNTAINS, BC

The forefield of Castle Creek in the Caribou Mountains of B.C. contains abundant well developed small-scale glacial landforms. Detailed maps of flutes and annual moraines were produced from aerial photography and selected flutes were mapped in the field, together with sedimentological and fabric analyses. The results revealed a number of flutes with differing morphologies; long parallel-sided flutes and shorter tapering flutes, which become shorter and narrower with distance down flute, exist in different areas of the forefield. In addition there are flutes with bedrock ridges at their ice proximal ends, which appear similar to crag and tail features. Grain size and fabric patterns within flutes, were similar to those found by Benn and Evans (1996) from studies in Europe and support the sediment deformation hypothesis of Boulton (1987). These results highlight the importance of grain size and pore water pressure in creating conditions for deformation to occur

The influence of particle shape on bedload transport in coarse-bed river channels

This thesis investigates the influence of bed material shape on sediment transport in gravel-bed rivers. The approach involves a combined series of field and laboratory experiments. Magnetic tracing experiments were carried out at three experimental sites in two Pennine gravel-bed streams. The specific aim of these experiments was to quantify the selective transport of different shapes of coarse river gravel and determine their spatial sorting within a natural stream channel. A total of 900 tracers in three size groups (32- 64 mm, 64-128 mm and greater than 128 mm) and four shape classes (spheres, blades, rod and discs) were prepared for each of the three sites. In die laboratory, tilting table experiments were carried out to clarify the mechanistic behaviour of different particle shapes, sizes and orientations on a variety of artificial and naturally formed bed roughnesses. Using strobe-light photography visualization experiments were undertaken with natural and artificially-moulded gravel-size particles of differing shape, size and weight in order to investigate the influence of shape on settling, grain impact, initial motion and transport paths of gravel-size particles. Results of the magnetic tracing experiments showed that there was both size and shape selectivity in bedload transport. Preferential movement occurred in die small and medium particle size classes with tracers concentrated along the channel thalweg. Sphere-shaped particles were transported the greatest distance and in greatest numbers. Rods also moved preferentially, while discs showed a lesser degree of transport and blades hardly moved at all. Results from the tilting table experiments highlight the importance of roundness as well as particle form and particle orientation in continuing thresholds of entertainment. In terms of size, friction angle was found to depend on the ratio of the diameter of the test particle to be moved to that it rests upon (d/D). Shape and orientation were found to be important parameters influencing friction angles. On a given bed roughness and for a constant size non-spherical test particles showed greater friction angles than spherical ones. A very clear difference was found in friction angle distibutions between sphere, transverse rod and other flat-shaped particles, namely, blades with parallel and transverse orientations, disc, and rod with parallel orientations. Visualisation experiments indicated that shape is an important particle characteristic that has a significant effect on settling rates and also the mode of near bed transport. These effects increase with greater particle sizes. The departure of a particle from a sphere leads to a decrease in its settling velocity, Experiments, across a range of test sizes showed that when compared to a sphere of equivalent weight and density, sphere and rod-shaped particles tend to settle the fastest and move by rolling. Discs and blades showed slower settling rates and, in most instances, moved by sliding. Experiments carried out with irregularly-shaped, natural particles show greater variability in settling behaviour and irregular patterns of motion. For every size group, sphere and rod shaped particles have lower critical angles of initial motion flian blade and disc-shapes. Regardless of shape, greater bed roughness, or decreasing particle size results in an increase in the critical angle for motion

Depositional architecture and petroleum potential of the Cambro-Ordovician Hawaz Formation, Murzuq Basin, SW Libya.

The Murzuq Basin, SW Libya, contains a sedimentary fill up to 4000 m thick, comprising a marine Palaeozoic section and a continental Mesozoic section. The primary reservoir target in the basin is the Upper Ordovician Mamuniyat Formation, but where this is missing the Middle Ordovician Hawaz Formation is the primary target, as in parts of the study area. The present study is based on slabbed cores, photographs, core samples, wireline log data and conventional core analysis of the Hawaz siliciclastic sediments. The petrology, textural properties, facies analysis, wireline log response and sequence stratigraphy of the Hawaz Formation suggest that the sandstones are mainly quartz arenites with some arkoses, derived from a similar parent rock, and deposited in shallow marine shoreface and shelf environments. Dynamic interaction between shoreface and shelf along a NW-SE oriented shoreline, probably fed by braided streams and braid delta systems, led to a frequent repetition of depositional facies, within a dominant transgressive setting. Sequence stratigraphie analysis of the Hawaz Formations shows that it comprises two transgressive systems tracts, two highstand systems tracts and a possible low stand erosion surface, beneath transgressive lower shoreface sediments. The position of the maximum flooding surface between the upper transgressive systems tracts and the succeeding highstand systems tract is controversial. Some authors place it in the upper part of the Hawaz Formation; others place it in the Silurian Tannezuft hot shales. In this study it is located at the base of the Silurian Tannezuft hot shales Sediment composition, regional facies patterns and sequence stratigraphie analysis suggest that the Hawaz sandstones were derived from a tectonically active, granitic basement source terrain, which was most probably the uplifted Chat/Tikiumit Arch, some 150 km southwest of Concession areas NC115 and NC 186. The lower part of the cored succession has the best reservoir properties

Intrinsic Properties and Fabric Anisotropy of Sands

The intrinsic properties and fabric anisotropy of sands significantly affect their macroscopic engineering behavior including packing densities, compressibility and strength. However, due to difficulties in reliably and rapidly determining them, intrinsic properties such as gradation, particle roundness and sphericity as well as the related fabric anisotropy of soils have not received their deserved attention and usage in practice. This dissertation introduces research that has facilitated rapid and precise quantification of soil properties and fabric anisotropy using various newly developed image analysis techniques. Extensive laboratory tests were performed on sands of various gradations, roundnesses, sphericities and geologic origins to develop relationships between their intrinsic properties and macroscopic mechanical behavior. A gradation-shape-fabric based Distinct Element Modeling technique was developed to simulate the properties and fabric anisotropy of soils. Besides geotechnical engineering, the technique can be used by engineers and scientists in various disciplines including material science, geology, mining, powder sciences, pavement engineering and agriculture to simulate more realistic material particle geometries and microstructures.PHDCivil EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138645/1/junxing_1.pd

The Continental Shelf: a Conveyor and/or Filter of Sediment to Deep-Water?

Outcrop and core-based studies of clinothems provide valuable archives basin-margin evolution. However, published quantitative grain character data (including grain size, grain shape, sorting, and sand-to-mud-ratios) are limited, and grain character variation across complete clinothem systems remains poorly constrained. Novel quantitative grain character datasets are presented here for core (Miocene intrashelf clinothems, offshore New Jersey) and outcrop (Eocene clinothems, Sobrarbe Deltaic Complex, Spain) case studies, which target quasi-coeval topset, foreset and bottomset deposits of prograding clinothems. Grain character datasets reveal that basin-scale and intraclinothem variations in sedimentary fabric are dependent on the dominant process-regime in operation at the shelf-edge. At basin-scales, shelf process-regime plays a more important role than clinoform trajectory in determining the location and timing of coarse-grained sediment delivery; river-dominated clinothems effectively convey coarse-grained sediment downdip under both rising and falling clinoform rollover trajectories. At intraclinothem scales abrupt stratigraphic changes in process-regime significantly impact the distribution of grain character across the complete depositional profile, forming observable and quantifiable intraclinothem chronostratigraphic surfaces. The grain-character dataset has been used to: i) compile unique databases of grain size, grain shape, and sorting statistics, which can be applied to test and refine numerical forward models of sediment distribution, which seek to improve prediction of lithology distribution; ii) quantitatively define intraclinothem surfaces at a higher resolution than is possible using chronostratigraphic techniques; iii) refine the placement of sequence boundaries, and iv) develop a model of clinothem evolution, in which the nature of the flows, and dominant process-regime in the shelf, control the downdip and vertical distribution of sand and mud. This study challenges widely held paradigms that link accommodation, sediment supply, and clinoform rollover trajectories to the distribution of sediment on basin margins. The results highlight the critical role played by the shelf process-regime in determining how and when sediment of different calibre and maturity is transported downdip