Impact of diagenesis on the reservoir rock quality of the Cachiri Group tight sandstones in Cesar sub basin (Colombia): A case of study from ANH-CR-MONTECARLO 1X well

Abstract

Basal sandstones of the studied interval in the Cesar Sub-basin (Colombia), have reported manifestations of hydrocarbons in the ANH CR MONTECARLO 1X well, so they have been studied as a possible unconventional reserve rock. Diagenesis plays an important role in assessing the quality of a reservoir rock, so this study presents an analysis of the diagenetic evolution in basal sandstones of the Cachiri Group in Cesar Sub-basin. Based on the petrographic and core data, diagenetic products have been determined, and how these have intervening in the quality as a possible reservoir rock. These sandstones with fine to medium grain sizes, poor to the moderate selection, are classified as arches and lithic arches. Core data porosity reveals a range between 0.06 and 2.1% and a permeability of 0.02–0.049 millidarcys (mD). These low porosity and permeability values are mainly controlled by the mechanical compaction process. Cement precipitation (carbonate, silica) also leads to a reduction in the porosity and permeability of these rocks. Other diagenetic products that can be evidenced in these sandstones are related to the metasomatism of feldspar grains by carbonate and ferrous carbonate, and dissolution of feldspar and lithic fragments.