Unconsolidated sediment

If we consider a well trajectory from surface to total depth (TD) it is sensible to look at the shallow section and the intermediate and reservoir intervals separately. The shallow section, usually referred to as top hole consists of rather unconsolidated sediments, hence the formation strength is low and drilling parameters and equipment have to be selected accordingly. 

Ruch, R.R. Kennedy, E.J. Shimp, N.E. Distribution of Arsenic in Unconsolidated Sediments from Southern Lake Michigan. Environ. Geol. 1979 Notes 37, 1-16. 

Manheim, F. T. (1970). The diffusion of ions in unconsolidated sediments. Earth Planet. Sci. Lett. 9, 307-309. 

The (compositionally) simplest mineral class comprises the native elements, that is, those elements, either metals or nonmetals that occur naturally in the native state, uncombined with others. Native gold, silver, and copper, for example, are metals that naturally occur in a ductile and malleable condition, while carbon - in the form of either graphite or diamond -and sulfur are examples of nonmetallic native elements. Next in compositional complexity are the binary minerals composed of two elements a metal or nonmetallic element combined with oxygen in the oxides, with a halogen - either fluorine, chlorine bromine, or iodine - in the halides, or sulfur, in the sulfides. The oxide minerals, for example, are solids that occur either in a somewhat hard, dense, and compact form in mineral ores and in rocks, or as relatively soft, unconsolidated sediments that melt at moderate to... 

Loss of sample in saturated or partially saturated unconsolidated sediments during extraction ... 

Littlefield, K. V., Wehler, N. E., and Heard, R. W., 1984, Identification and Removal of Hydrocarbons from Unconsolidated Sediments Affected by Tidal Fluctuations In Proceedings of the National Water Well Association Fourth National Symposium on Aquifer Restoration and Ground Water Monitoring, pp. 316-322. 

In weakly consolidated, stratified sediments, the injection pressure must be controlled so that the surrounding formation is not fractured. If fracturing occurs, there is usually a severe loss in hydraulic conductivity because the bedding planes are disturbed. Pressures that will cause fracturing range from a low of 0.5 psi/ft of depth for poorly consolidated coastal plain sediments, to 1.2 psi/ft depth for crystalline rock. For most recharge wells in unconsolidated sediments, the injection pressure should be carefully controlled so that the positive head (in psi at the surface) does not exceed 0.2 x h, where h is the depth (in ft) from the ground surface to the top of the screen or filter pack. 

Significant amounts of manganese and phosphorite deposits are present on the top of the Blake Plateau, which lies at the foot of the continental margin off the southeastern United States at depths of 500 to 900 m. The Gulf Stream has eroded most of the unconsolidated sediments at this location, leaving only a carbonate platform, which has become covered with pavements of manganese and phosphorite covering an area of 5000 km ... 

Nonionizable chemicals (e.g., hydrocarbons, ethers, alcohol) that sorb onto organic materials in an aquifer (i.e., organic carbon) are retarded in their movement in groundwater. The sorbing solute travels at linear velocity that is lower than the groundwater flow velocity by a factor of Ra, the retardation factor. If the Koc of a compound is known, the retardation factor may be calculated using the following equation from Freeze and Cherry (1974) for unconsolidated sediments ... 

The Waterloo Barrier does not remediate wastes. The contaminant plume must be small enough for enclosure to be practical. The vibration and noise associated with pile driving equipment may be a problem in densely populated areas. Funnel-and-gate system can be problematic because they alter groundwater flow. In bouldered terrain and very dense unconsolidated sediments, the use of sheet piling may not be possible. Steel sheet pile applications are generally restricted to depths of less than 30 m. At some sites it is necessary to seal the barrier system to bedrock. 

Hamilton (1959) has shown that a 150-700 meter-thick layer of unconsolidated sediments exists even on most deep sea floors. Let us consider a little more closely then the difference between the "open" sea situation, where sedimentary clays are in contact with sea water of roughly constant composition and an unconsolidated sediment which contains a pore fluid. 

CLAYS. The terms chy or cloys commonly refer to cither rocks that are consolidated or unconsolidated sediments, nr a group of minerals having unique properties. Traditionally, clays (rocks) are distinctive in al least two properties that render them technologically useful plasticity and composition. Clays are predominantly composed of hydrous phyllosilicates. referred to as clay minerals. These are hydrous silicates of Al. Mg. K, anti He. and other less ahundanl elements. Clay minerals arc extremely fine crystals or particles, often colloidal in size and usually plate-like in shape. The nonclay mineral portion of clays (rocks) may consist of other minerals, portions of rocks, and organic compounds. 

FIGURE 2.17 Thermal conductivity of gas, water, ice, and hydrates (a) without and (b) with unconsolidated sediment (Gupta, 2007). 

While the AVO technique can be used to determine the phases at the BSR interface, Nur and coworkers (Dvorkin and Nur, 1992 Ecker et al 1996) used AVO to determine that hydrates were usually located away from grain contacts, only partially filling the pore space. That is, in theory, hydrates typically do not cement the grains of unconsolidated sediment, when reflections are weak and permeability is low. 

Cundy, A.B. and Hopkinson, L. (2005) Electrokinetic iron pan generation in unconsolidated sediments implications for contaminated land remediation and soil engineering. Applied Geochemistry, 20(5), 841-48. 

Manheim, P. T. (1966). A hydraulic squeezer for obtaining interstitial waters from consolidated and unconsolidated sediments, pp. 550—556. USGS, Washington. 

Apparatus for testing the permeability of samples of unconsolidated sediments in the field. U. S. Geol. Survey. (Processed.)... 

OVERBURDEN GEOLOGY From inferred nature of unconsolidated sediments would leachate occurrence be likely to increase or decrease human exposure to pollutants ... 

Russell, B. F., Phelps, T. J., Griffin, W. T. Sargent, K. A. (1992). Procedures for sampling deep subsurface microbial communities in unconsolidated sediments. Ground... 

Barnes R. O. (1973) An in situ interstitial water sampler for use in unconsolidated sediments. Deep-Sea Res. 20, 1125-1128. 

Mineral precipitation within primary intergranular pore spaces leads to cementation. The existence of cements demands elemental mobility at least on the scale of a thin section, because cements reduce porosity that was present at the time of deposition. During early diagenesis of unconsolidated sediments, displacive cementation may lead to cement volumes in excess of 45%. In late diagenesis the upper limit of cement volume is constrained by the IGV at the time of cement emplacement. 

Much higher concentrations of arsenic frequently occur in pore waters extracted from unconsolidated sediments than in overlying surface waters. Widerlund and Ingri (1995) reported concentrations in the range 1.3-166 p.g in pore waters from the Kalix River estuary, northern Sweden. Yan et al. (2000) found concentrations in the range 3.2-99 p.g in pore waters from clay sediments in Saskatchewan, Canada. 

Silcrete may form within, or by the replacement of, a range of host material types. Many Australian and South African silcretes have developed within deeply kaolinised or bleached regolith (Summerfield, 1978 1983b-d Wopfner, 1983 Milnes and Thiry, 1992 Thiry et al., 2006). Formation can, however, occur in (or on) unweathered bedrock or otherwise unaltered and unconsolidated sediments. Silcrete development is also frequently associated with the replacement of carbonate sediments or calcretes (Cros and Freytet, 1981 Twidale and Milnes, 1983 Ribet and Thiry, 1990 Armenteros et al., 1995 Nash and Shaw, 1998 Thiry and Ribet, 1999 Nash et al., 2004). 

---