Compaction Grain Research Articles

COMPARISON OF POROSITY‐DEPTH RELATIONSHIPS OF SHALE AND SANDSTONE*

The rate of shale compaction or porosity reduction decreases with increase in burial or compaction. This may be caused by decreasing shale permeability and increasing water viscosity, thus decreasing rate of fluid expulsion with increasing compiction. For a given increase in overburden pressure, the pressure or stress applied to a given grain‐to‐grain contact area decreases with burial becaused the contact area increases with compaction and concomitant grain deformation. This may also cause the reduced rate of compaction with increase in burial. The above abservations may suggest that the shale compaction is primarily controlled by physical forces of sedimentary rocks.On the contrary, the rate of sandstone porosity reduction is known to be relatively constant throughout the burial diagenetic history in many regions provided ther was no significant secondary porosity developed by leaching and fracturing. For a given increase in overburden pressure, the grain‐to‐grain contact area. Yet, rate of porosity reduction for the sandstones is realtively constant, whether they are at a shallow or deep burial depth. This suggests that, for the sandstones, the physical forces have been of secondary importance in reducing the porosity. Chemical and mineralogical agents are believed to have been more significant in sandstones. Numerous regional petrographic studies confiirm the importance of diagenetic cements.

Pressure sintering of GaSb

GaSb with nearly theoretical densities has been hot pressed at 25,000 psi and 690°C. The compaction mechanism of coarse GaSb particle matrices (20–500μ) is largely one of plastic flow. However, GaSb powders with average particle diameters below 4μ compact according to a mechanism that involves the surface dissociation of GaSb resulting in the presence of liquid Ga. The liquid phase leads to a high compaction rate and grain regrowth.