Sediments compaction

Growth faulted deltaic areas are highly prospective since they comprise of thick sections of good quality reservoir sands. Deltas usually overlay organic rich marine clays which can source the structures on maturation. Examples are the Niger, Baram or Mississippi Deltas. Clays, deposited within deltaic sequences may restrict the water expulsion during the rapid sedimentation / compaction. This can lead to the generation of overpressures. 

As water is removed from the spaces between soil particles, the sediments compact and the ground surface is lowered—it subsides. In areas where groundwater withdrawal has been extreme, the ground surface has subsided significantly. In... 

Bayer, U., 1989. Sediment compaction in large scale systems. Geologische Rundschau 78/1, pp. 155-169... 

The average vertical distributions of solid-phase Fe or Mn are determined by biogenic and physical reworking, net sedimentation, compaction, and dissolution-precipitation reactions. These distributions can... 

Sediment compaction and a resnlting flow of water towards the sediment snrface. 

At present this compaction driven model is still widely used and implemented in modem basin modelling tools. The most important assumption in these models is that the depositional overburden load is the cause of compaction of the deeper layers (lES 1996). The overburden is responsible for the stress field in the basin. The driving force for sediment compaction in these models assuming a single axis stress tensor is the effective stress (cr) as the difference between overburden (S ) and pore pressure (P) (equation (1)). This forms the basis for the compaction law defined in equation (2). 

BJprlykke, K., F Chuhan, A KJeldstad, E Gundersen, O Lauvrak and K Hpeg, Modelling of sediment compaction and fluid flow during burial in sedimentary basins, this volume, 2004. 

MODELLING OF SEDIMENT COMPACTION DURING BURIAL IN SEDIMENTARY... 

The most important factor controlling sediment compaction is the sediment composition since both the mechanical and the chemical processes are so dependant on the lithology. 

Mechanical compaction of sediments includes the rearrangement and breakage of grains which is a function of the overburden stress. Sediment compaction and fluid flow are coupled because the reduction in porosity requires a removal of fluids. 

Other processes can not be coupled because they are principally very different in terms of driving forces. A model attempting to include all the processes involved in sediment compaction would be far too complex, and practical predictions should be based on an identification of the quantitatively most important processes. 

Realistic modelling of sediment compaction during burial is difficult because several very different processes are involved. Modelling of compaction in sedimentary basins is very dependent on the primary lithology because each layer may have very different mineralogy and textural characteristics controlling mechanical and chemical compaction. 

The physical processes involved in sediment compaction and fluid flow are in principle well understood but more experimental data on compaction of different types of sediments are required. Great progress has been made in recent years in modelling of chemical compaction particularly for quartz-rich sandstones. 

Within subsiding continental basins, groundwater can be induced by sediment compaction (pressure water) and by driving forces from topographic relief or from variations in fluid density. The intensive water flow can disturb the thermal profile and change the time-temperature history of buried source rocks. Maximal rate of pressure-water expulsion (Rpwe) can be estimated relatively easily using Eqs. 6.i and 6.2 for the case of one-dimensional consolidation of homogeneous sediments on immobile basement ... 

The two rocks that can generate diapirs are the evap-orites and overpressnred clay. The evaporites commonly have a density of abont 2.03 g/cm. This is greater than that of freshly deposited sand and clay. Bnt as normal sediments compact, their density exceeds that of evaporites at about 800 m of burial. Below this depth, therefore, di-apiric deformation may be expected to commence. Movement may be initiated by stractnral forces, but can also apparently occur spontaneously. 

Transition zones occur in many types of strata but are particularly common in sedimentary rocks. A transition zone occurs when some change in deposition causes a change in sedimentation. Different types of sediments compact at different rates. Discontinuities are abundant in the transition zones between distinct strata. For example, where ancient streambeds eroded the adjacent sediments, remnants of the stream channel disrupt the continuity of the normal roof beds, resulting in large slip planes. 

Hermawan, M., BnsheU, G, Bickert, G and Amal, R. (2004). Characterisation of short range strncture of sdica aggregates - implication to sediment compaction. International Journal of Mineral Processing, 73, 65-81. 

Storm surges powered by tropical storms and hurricanes can wreak havoc along low-lying coasts. The settlers who founded New Orleans in 1718 along the lower Mississippi River experienced their first major flood the same year. Over time, many other floods have occurred in New Orleans and the lower reaches of the Mississippi, aided by the slow sinking of the floodplain as river sediments compact over time. 

The equipment has a horizontal cylindroconical bowl and for this application it usually works with countercurrent circulation of the sediment and the centrate. A relative velocity of the bowl and the extraction screw of 3 to 30 rpm regulates the sediment compaction time. Accelerations vary between 1000 and 1500 G. 

For a structured suspension, obtained by controlled flocculation or addition of thickeners (such as polysaccharides, clays or oxides), the floes sediment at a rate dependent on the size and porosity of the aggregated mass. After this initial sedimentation, compaction and rearrangement of the floe structure occurs, a phenomenon referred to as consolidation. 

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