Normal formation pressure gradient

The normal formation pressure gradient is the density of a column of saltwater of length Zy is expressed in psi-ft in customary units. Table 4-134 gives normal gradient values for areas around the world. Note that for freshwater or quasi-freshwater Gj = 0.433 psi/ft = 8.345 Ib/gal. 

Normal Formation Pressure Gradients in Various Areas [101]... 

Finally, the last two terms on the r.h.s. are needed If the potential and the pressure gradients In the normal direction are considered, when no fluid flow occurs In that direction. This is often the case because the surface cannot act as a source of liquid (o = 0 at x = 0). Formation of a diffuse layer leads to local excesses of ions exerting a certain osmotic pressure, which Is just equal and opposite to Vp, because otherwise the liquid would start to flow. Equation 14.6.6) then reduces to... 

A major role of low interfacial tensions in enhanced oil recovery is to facilitate the removal of small oil drops entrapped in pores that have been wetted by water. The interfacial tension between water and a common crude oil is about 30 mN/m, and typical pore sizes may be in the range of 10 mm, so that the capillary pressure, as calculated with Eq. (10.10), retarding flow of the trapped oil will be greater than the normal pressure gradients encountered in oil formations. In discussions of liquid flow through capillary systems, it is common to refer to the capillary number, which is the ratio of the surface tension of the liquid to its viscosity. A small capillary number implies easier flow through the system, so that a reduction in interfacial tension should produce an improvement in oil extraction. 

Still, Smorbukk, which we advocate had experienced an event of leakage, remains oil filled today throughout, apart from the Gam Formation. Furthermore, Smorbukk Sor is oil-filled despite evidence for leakage into the Cretaceous strata above. The nearby Kristin field is overpressured but is sufficiently deep as to avoid the fracture gradient, and contains a condensate as does the normally pressured Lavrans (Fig. 5), which all, accordingly fall into Scenario-1 in Fig. 7. 

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