Compaction and cementation of quartz sands and natural sandstones have been studied experimentally under conditions simulating deep burial. Approximately 230 experiments, lasting a few hours to 100 days, were successfully completed.
Compaction, resulting in loss of porosity, comes about largely by mechanical fracturing, rotation, and interpenetration of grains. High temperatures and the presence of distilled water and alkaline saline waters facilitate compaction. Flowing solutions are more effective in this respect than are static solutions.
Cementation occurs more or less independently of compaction. Again, flowing solutions are the most efficacious. Very little cementation resulted from any of the experiments with distilled water. With sea water and saline-formation waters the degree of cementation is a function of temperature and develops with increasing rapidity above 270°C. If it occurs at all, the cementation is apparent within the first 24 hours.
The fabric of many natural sandstones suggests that compaction has been brought about primarily by solution of quartz grains at points of contact. We were unable to demonstrate this process experimentally, however, although it may have occurred to some degree in experiments at high temperatures with flowing solutions. One experiment involving an alkaline solution of colloidal silica duplicates the fabric of a natural sandstone quite closely, in that the fractures resulting from compaction apparently have been healed by deposition of secondary quartz. It is suggested that mechanical straining, fracturing, and crushing of quartz grains at points of contact, followed by solution of the strained and fractured quartz and healing of fractured grains, may be important in consolidation of natural sandstones.
An anomalous increase in apparent compressive strength of quartz with rising temperature was observed in the interval between 235° and 270°C. This effect is possibly related to incipient plastic deformation of the quartz grains and may be a factor in the preservation of porosity of deeply buried sandstones.