Abstract

The formation evaluation in a primary formation of a CO2 sequestration project in Western Australia has been very challenging due to the presence of glauconite and other iron rich minerals. The conventional method cannot handle the mineralogy effects, hence the accurate porosity, clay type and clay content cannot be calculated accurately. The latest generation in spectroscopy technology LithoScanner was brought to the project and run in well A for the first time in Australia. The tool has a high output pulse neutron generator and unique cerium-doped lanthanum bromide (LaBr3:Cr) gamma ray detector. This combination enables the tool to measure both inelastic and capture spectra for an expanded set of elements from that of previous-generation tools. We are measuring elements that make up more than 99% of the average abundance in the earth’s crust. Measuring the elements is the starting point to calculate minerals, matrix density and those are key to obtain accurate reserves estimates (porosity) and build an accurate petrophysical and reservoir model. For well A, the LithoScanner elements weight fractions are used in the Techlog QuantiElan module to solve mineralogy that includes quartz, K-feldspar, calcite, siderite, pyrite, illite, kaolinite, glauconite and chlorite. There is a very good agreement between the computed mineralogy and the mineralogy from core measurements. LithoScanner provides a continuous log of matrix density that is used as an input to porosity calculations. This formation evaluation based on Litho Scanner does not require the subjective inputs from the log analysis, but completely rely on the tool’s reading. It can be used for both simple and complex formation to obtain the good consistency and accurate answers.

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