Limestone matrix

Such investigations assume greater importance in dealing with siliceous limestones. For such materials it is necessary to ascertain the distribution of the quartz in the limestone matrix. The type of intergrowth and the grain size of the constituents can be determined in thin sections under the microscope. 

If the neutron tool is calibrated for such a limestone matrix and pore fluid freshwater, then... 

FIGURE 5.19 Calculated neutron-density crossplot x-axis gives the neutron porosity for a limestone-calibrated tool y-axis gives the bulk density. Lines are plotted for sandstone/quartz (matrix density 2.65 g/cm, matrix neutron response —0.03) limestone (matrix density 2.71 g/cm, matrix neutron response 0.00) dolomite (matrix density 2.86 g/cm, matrix neutron response +0.04) freshwater (density 1.00 g/cm, neutron response 1.00). 

FIGURE 6.32 Compressional velocity as a fimctirai of porosity for inclusions filled with gas (left figure) and water (right figure), calculated fra- different aspect ratios (0.10, 0.15, 0.20, and 0.05). Input parameters are (limestone matrix) ts=73GPa, /Js=32GPa, = 0.01 GPa,... 

A high neutron porosity and low density porosity occur in the shale zones 2256-2274 and 2356-2388 ft. In the clean zone, around 2280-2290 ft, the cleanest part reads = 18% and = 13%. Plotting the point in the CNL chart of Figure 4-303, the rock matrix appears to be a dolomitized limestone and the true porosity is 17%. 

Table 4.11. Eigenvalues of the correlation matrix of major-element concentrations in Coumiac limestones and percentage of variance explained by each component.

In the grain model, it is assumed that the CaO consists of spherical grains of uniform size distributed in a porous matrix. The rate of reaction is controlled by the diffusion of SO2 through the porous matrix and the product CaSO layer formed on each grain (11). Allowance can be made for a finite rate of the CaO/SC reaction (12). The models have been found to describe experimental data for many limestones (13) by adjusting the constants in the model, most notably the diffusivity through the product layer. 

Lumachella is a similar material of iridescent, multicoloured shell, though it is not as spectacular as ammolite. It tends to appear more as fragments in a matrix of limestone, giving an effect of marble with iridescent patches. It is found in Italy and Austria and is used as a decorative marble - sometimes in mosaics. It is not used for setting in jewellery. 

This matrix acidization process consists of injecting hydrochloric acid (for limestones) or a hydrochloric acid-hydrofluoric acid mixture (for sandstones) into the formation pore space. The acid reacts with and dissolves portions of the original rock matrix and thus increases permeability. The depth that the acid penetrates into the formation is one of the factors that determines the effectiveness of the treatment. 

Very simply, a sandstone has a grain composition of stone detritus (quartz, feldspar, detritic mica/clays) and a binder that may be clayey, quartzitic, or carbonatic (or mixtures thereof) [51, 55]. The mineral composition of limestone is mostly calcium carbonate, often derived fi om precipitated calcium carbonate and fossil shell remnants fi-om marine organisms and a calcitic binder matrix [51, 56, 57]. 

Micrite (micritic) the semiopaque, micro-crystalline interstitial component (matrix) of limestones consisting of precipitated carbonate (calcite) mud. 

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