Writers : Berner,Robert L.;Moussavi Harami, Reza
Refference : Geosciences Scientific Quarterly Journal,No.8
Publishing Year : 1372

Abstract :
Diagenetic alterations of fluvial sandstones from three sedimentary basins, with different paleoclimate, were studied. Sandstones of Shurijeh Formation (Lower Cretaceous) in eastern Kopet-Dagh basin of NE Iran, was compared to Upper Carboniferous (Pennsylvanian) sandstones in the Midoontinent and the sandstones of the Parkman Formation (Upper Cretaceous) in the western interior of the United States.
Sandstones of Shurijeh Formation were deposited under arid and warm conditions in fluvial environment. Thus, the meteoric waters were alkaline and during the early diagenetic stage, calcite and anhydrate cements along with infiltarated clays reduced the reservoir properties of these sandstones. The Upper Pennsylvanian sandstones were deposited under humid, subtropical conditions. Because of the very humid conditions, vegetation was abundant in the region and decomposition of organic matter caused the meteoric waters to be acidic. Petrographic evidence indicate that the circulation of Low PH, organic-rich water through an open hydrologic system caused early feldspar dissolution. Feldspar dissolution in these sandstones produce secondary porosity and is responsible for their ability to serve as petroleum reservoirs. Sandstones of the Parkman Formation were deposited in fluvial-deltaic system under humid, temperate climatic conditions. fluvial sandstones of this formation were exposed to acidic waters in an organic-rich enviroment. In these sandstones, secondary porosity was not created and kaolinite pore-fillings derived from dissolution of feldspars also destroyed primary porosities. Silica cement in fluvial sandstones, that lack diagenetic chlorite coatings, also destroyed the porosities and permeability.
It is concluded that chemical properties of meteoric water effects the diagenetic alteration of the sediment during the early diagenetic history. In fluvial systems., chemical qualities are determined to a large extent by climatic conditions of the region. Therefore, climate can be very important in controling the reservior properties of fluvial sandstones.
Subject List : Source Properties