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ADVANCED TECHNIQUES FOR DETERMINING PARAMETERS OF INTEREST IN THE SHALE GAS EXPLORATION

Dumitru Frunzescu

Abstract

During the last years, under Schlumberger brand, several methods have been refined for determining detailed characteristics of geological formations, as they are necessary in the assessment of shale gas potential based on drilling core investigations, wells diagraphies investigations, seismic investigations, and combination of all these. The correct determination of lithofacies of the cores leads to a quality diagnosis of shales reservoirs. The accurate mineralogy input is obtained by Litho Scanner in the sCore lithofacies classification system which generate a log display of the classification and the reservoir and completion quality indicators (such as porosity, total organic carbon = TOC, fracture density and stress) overlaid on the cores ternary diagram. Between key reservoir parameters of the shale gas assessment (thermal maturity, reservoir thickness, TOC content, adsorbed gas fraction, free gas fraction in the pores and fractures, and permeability), thermal maturity is measured in core analysis, reservoir thickness is measured with well logs, and the last parameters requires an advanced approach that implies investigation platforms logging tools of different parameters such as Elemental Capture Spectroscopy (ECS) and Elemental Log Analysis (ELAN). These investigation platforms provides clay content and matrix density, quantify kerogen, porosity and gas saturation. It is necessary calibration to cores for thermal maturity and a metric to equate TOC to adsorbed gas. The amount of adsorbed gas is a function of kerogen content, pore pressure, and temperature. Clay quantification, in terms of clay minerals content and petrophysical properties it is related by aluminum content, and the solution is SpectroLith application, that sums up a series of empirical relationships that provide clay, carbonate, pyrite, and quartz-feldspar-micas weight percent. Elemental Capture Spectroscopy is a geochemical log that quantifies chemical elements, and his investigation is maximized by SpectroLith. The kerogen can be accurately estimated through merging of a conventional triple combo log with a geochemical log that allows the calculation of mineral content, and an estimate of key petrophysical properties (porosity, saturation and permeability). Minerals content calculated by SpectroLith application can be readily incorporated in a petrophysical interpretation program named ELAN. In the assessment of shale gas also aims to quantify the adsorbed gas as well as quantify of free gas, depending on reservoir pressure, porosity and gas saturation obtained by ELAN program. The gas producibility assumes besides the drilling of vertical wells, horizontal wells and hydraulic fracturing using of advanced methods and instruments of shale gas analysis. In the paper there are underlined several advanced techniques for determination of some parameters with large applicability in the shale gas exploration.

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