Geochemical Logging: A Middle East Case Study of a New Logging Tool

Abstract

While the traditional “Triple Combo” measurements remain a formation evaluation mainstay, in more complex environments many assumptions are made during the interpretation work. Lithology is interpreted from density, Pe, GR and neutron logs assisted by other sources of information such as cuttings and core analysis, however there are many limitations. Interpretation models can be refined with direct knowledge of elemental concentrations which are used to solve for complex mineralogy. For example, in a carbonate reservoir, a direct reading of Magnesium weight percentage provides a valuable measurement of Dolomite volume. Similarly, Sulphur fractional information provides knowledge of Anhydrite distribution. Geochemical logging provides a direct measurement of elemental concentrations and compliments the typical density, Pe, GR and neutron logs. The latest generation logging tool resolves a wide-range of elements including the traditionally more difficult-to-measure Magnesium and Aluminium weight fractions. In this paper we introduce a new Geochemical Elemental Tool with examples taken from both Siliciclastic and Carbonate Middle-East reservoirs. The important Permian age Siliciclastic reservoir studied is an eolian dune and interdune facies, which contains varying volumes of diagenetic anhydrite cement, feldspar and Illite. The elemental concentration of Silicon, Potassium, Sulphur and Aluminium are inputs used to solve for these minerals in the lithology model. We demonstrate the accuracy of the elemental weight fraction from the logging tool results by comparison to ICP & XRD measurements made from core. In addition results are presented of the mineralogy interpretation from the case study wells.