Petrographic analysis of the sandstones of the Cushabatay Formation. Marañón Basin. Tangarana1 well, Loreto

Abstract

This work presents the petrographic analysis of the sandstones belonging to the Cushabatay Formation (Lower Cretaceous) in the Tangarana1 well, in the Marañón Basin (Loreto, Peru), which was carried out using optical microscopy and electron microprobe techniques for the measurement of detailed petrographic and textural characteristics to determine its reservoir rock conditions. The petrographic results correspond to quartz-sandstone type sandstones, with a high percentage of quartz (> 95%) and a low percentage of feldspars and rock fragments, with a grain size from medium to coarse, with a degree of roundness from sub-rounded to sub-angular and moderate selection, clay matrix and clay cements, calcite, siderite, anhydrite, and iron oxides. The porosity values ​​in the Cushabatay sandstones vary from 7% to 14%, observing a good correspondence between the values ​​measured in the petrographic analysis and those obtained in the rock mechanics laboratory (from 6.5% to 13.5%), in some area’s porosity is influenced by the presence of matrix and clay cement and other cements, therefore the cushabatay sandstones have moderate conditions to be considered reservoir rock.