Diagenetic Traps in Sandstones

Abstract

Diagenesis may be an important agent in trapping hydrocarbons in sandstones by formation of reservoirs or seals. Reservoirs are formed by the creation of secondary porosity during burial. Seals are formed by heavy cementation, which may allow sandstones to retain large hydrocarbon columns. Formation of a diagenetic trap requires that parts of the sandstone unit react differently from each other during burial. This can be caused by differences in (1) detrital mineralogy--resulting from grain size or depositional environment controls; (2) early diagenetic mineralogy--largely depositional environment controlled; (3) burial history--structural movement induced; and (4) fluid content--hydrocarbon or water saturation. Each of these factors can lead to differences in porosity and permeability of the sandstone sufficient to form reservoirs and seals. In the correct configuration, diagenetic traps may be formed. Basin-center gas accumulations result from diagenetic trapping in some instances.