Mineralogical and morphological characterization of the Cretaceous Galembo Member mudstones of the La Luna Formation in the Middle Magdalena Valley Basin (Colombia)

Abstract

The development of shale oil/gas reservoirs has suffered constant changes, innovations and successive reactions, although it depends on the success of hydraulic fracturing, and mineralogy and morphology play a very important role in establishing brittleness and therefore controlling it. In this study, mineralogical and morphological characteristics of the Cretaceous Galembo Member Mudstones of the La Luna Formation in the Middle Magdalena Valley Basin (Colombia) have been characterized using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy to obtain information on mineral morphology, size, microfabric, microtexture, and elemental composition. The analyzed rocks can be classified in several lithofacies: Nonlaminated to slight laminated foraminifera wackestones, Moderate to well-laminated highly fossiliferous and organic-rich mudstones, Fossiliferous carbonate concretions, Nonlaminated siliceous and fossiliferous claystones, and Nonlaminated calcareous mudstones. In general, these rocks show fossil content typical from a predominantly deep marine paleoenvironmental conditions, although minor changes can generate variations in the relative proportion of terrigenous material, precipitation of organic matter and diagenetic alterations. They consist of calcite, mainly cryptocrystalline micrite, microcrystalline quartz, illite and kaolinite, with minor phosphates (apatite), sulfides (framboidal pyrite and sphalerite) and sulfates (barite). Porosity in the analyzed rocks can be found into matrix pores (interparticle pores between mineral particles and intraparticle pores within mineral particles) and microfractures.