Chemical compaction

After 15 years of studying the diagenesis of the sandstones of the Norwegian Continental Shelf, it is found that beyond a certain depth the main controlling force behind the diagenetic reduction of porosity may be temperature. The diagenetic changes involve widespread chemical compaction. One view is that this is caused by a precipitation rate-controlled process where quartz cement is derived from dissolution at nearby stylolites. Dissolved silica then diffuses short distances from sites of dissolution to sites of precipitation. The rate of quartz cementation is calculated empirically by the method of Walderhaug (1996). All that is needed to predict porosity loss in a sandstone with a certain quartz surface area is an estimate of the temperature history. Essential input to the model is a basin description and temperature history. A simplified model for chemical compaction is included in BMT.

 

 

 

 

 

 

 

 

Figure showing predicted porosity loss in sandstones by quartz cementation on a 2D section. The highest porosity loss of present day is at 3-4 km depth.