Scanning electron microscope description of the Afowo oil sand deposits in south-western Nigeria

The Afowo oil sand deposits in parts of Southwestern Nigeria were described by scanning electron microscope for characterizing the reservoir sands, based on their clay content. Twelvecoreoilsandsampleswerecollected,sixofwhichwereselectedforanalysisbasedonth esimilaritiesintheirphysical and textural characteristics. The prepared oil sand samples were then described by scanning electron microscope studies (VEGA TESCAN/LMU scanning electron microscope-SEM). The analysis revealed that the oil sands contained minerals which had been precipitated and occurred as pore filling cement; these minerals included sheet kaolinite, vermiform kaolinite, k- feldspar, pyrite crystals, and corrosion quartz and corrosion feldspar. The SEM images also showed 2-4 µm micro pores and 2-5 µm fractures. The study showed that the clay minerals contained in the Afowo formation's reservoir rocks were mainly kaolinite which was not expected to have any negative effects on reservoir quality, especially during enhanced oil recovery operations. Keywords: Tar sand, textural characteristics, kaolinite, fracture, pore cement, reservoir and clay. Los depositos de arenas bituminosas de la Formacion Afowo en algunas partes de suroeste de Nigeria fueron analizados con microscopio electronico para caracterizar las arenas del reservorio, basados en el contenido de arcilla. Doce corazones de arenas bituminosas fueron recolectados, de estos, se seleccionaron seis para analisis basados en las similitudes de sus propiedades fisicas y texturales. Las muestras de arena bituminosa preparadas fueron estudiadas con el microscopio electronico (VEGATESCAN/LMU Microscopio Electronico de Barrido-SEM). El analisis revelo que las arenas bituminosas contuvieron minerales que fueron precipitados y que llenaron espacios de poros con cemento; estos minerales incluyen caolinita laminar, caolinita vermiforme, feldespato potasico, pirita, cuarzo y feldespato corroido. Las imagenes SEM mostraron micro poros de 2-4 µm ay fracturas de 2-5µm. El estudio indico que los minerales arcillosos contenidos en la rocas del yacimiento de la Formacion Afowo, son esencialmente caolinita la cual no tiene efectos negativos sobre la calidad del yacimiento, especialmente durante las operaciones de recobro mejorado. Palabras clave: renas bituminosas, caracteristicas texturales, caolinita, fractura, cementado poro, deposito y arcilla.