MODEL-CALCULATIONS OF LOSS OF POROSITY IN SANDSTONES AS A RESULT OF COMPACTION AND QUARTZ CEMENTATION

A simple mathematical model has been developed for the precipitation of quartz cements along a dipping sandstone bed as a result of the cooling of a quartz-saturated formation water. The model assumes that the sand suffers a substantial loss of porosity through compaction before quartz cementation occurs, and that the cementation takes the form of an event of 10 Ma duration. The results suggest that flow-rates of metres to tens of metres per year need to be sustained over the 10 Ma period for a significant amount of quartz cement to precipitate. Such flow-rates are generally thought to be characteristic only of artesian flow.