ABSTRACT

Density of lattice water (mainly OH water) in the shales of the Beaufort Basin is estimated to be approximately 1.4 g/cm³, from the study of the porosity cross plot from neutron and density logs made by Youn (1974). It is interesting to note that this density value is quite close to that of bound or structured water closest to the clay surfaces under laboratory conditions (Martin, 1962).

The fact that the viscosity of bound water increases toward clay surfaces suggests that shales must expel more viscous water with increasing compaction. This may be one of the reasons for reduced rate of compaction at greater burial depths.

During continuous burial the quality of oil usually "improves" in the sense that the viscosity decreases. Therefore, at some point during continuous burial history the viscosity of water being expelled from shales may exceed that of the generated oil. If this happens, oil may move preferentially to water, thereby creating the conditions for significant primary oil migration.