Study of potassium-sodium and calcium-sodium field spars using x-ray methods

A comprehensive study of the lithological and petrophysical properties of rocks includes the following methods of research: petrographic, petrophysical, and methods of nuclear physics. The choice of petrophysical methods depends on their ability to determine desired minerals and non-mineral components. The research scheme is developed taking into account the description of core sections, a qualitative determination of the composition of the rock, as well as an approximate calculation of the areas occupied by the minerals in the thin rock section. In the analysis of complex reservoirs, in addition to standard estimates of porosity, permeability, water-holding capacity, etc., additional special studies are needed, e.g., to determine the quantitative content of minerals, it is necessary to use the methods of x-ray structural analysis, however here we faces a known problem of identification of the minerals by the captured diffractograms. It is known that the rocks of Western Siberia include mainly quartz, potassium-sodium and calcium-sodium feldspars. Feldspars are the most important family of rock-forming minerals, they make up to 60% of the volume of the earth’s crust (up to 50% of its mass). Most of the feldspars are included in the ternary system NaAlSi₃O₈ – KAlSi₃O₈ – CaAl₂Si₂O₈. All crystal structures of the feldspars are based on a similar Si – Al tetrahedral skeleton frame [AlSi₃O₈], and thus are almost indistinguishable in the diffraction patterns. A method of quantitative x-ray and phase analysis is developed for selective determination of the concentrations of calcium and potassium feldspars. A method for separating the peaks of the characteristic radiation of mineral elements is proposed. The conditions and optimal parameters of x-ray phase and x-ray fluorescence analysis are specified to determine the total mineral content and calcium concentration (using an X-ray tube with a titanium anode and a scandium filter).

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