Hydrostatic gradient

Amoco used nitrogen to confirm a safe method to remove gas trapped in a subsea BOP. The gas can be recovered up the choke line by displacing the kill mud with water and then allowing the gas to expand against the lower hydrostatic gradient of the water. 

Fig. 14. Relationships between pore-pressures, the hydrostatic gradient, the fracture pressure gradient (approximation to the minimal horizontal stress, Sf,) and the lithostatic pressure gradient (approximation to the vertical stress, S ). Pore-pressures from sea floor to base Pliocene equals hydrostatic. The yellow, dark blue and red pore-pressure trend-lines represent the pore-pressure versus depth gradients for the Paleocene-Eocene, Mid-late Cretaceous and Upper Jurassic-lowermost Cretaceous, respectively. The portion of the red trend-line below approximately 2550 m MSL equals the maximum reservoir pore-pressure trend-line of Fig. 13 and reflects the counter-pressure of the topseal controlling the pore-pressure distribution of hydraulic compartments II, III and (probably) IV.

Equation 6.12 can also be used to calculate the amount of methane that would account for the isotopic excursion assuming 513Cx = —60%o, a 8130(.arbonal(. excursion of—2 to —3%o would require 1.4—2.1 TtC, which amounts to 1.9—2.8 Tt methane. A deep-water temperature increase from 11 to 15 °C would move the upper stability depth for methane hydrates from c.920 to 1460m, assuming a hydrostatic gradient of lOkPam-1... 

Fig. 7. Trends of bubble point (Pj,) of oils with depth below top of oil column in single reservoirs with multiple wells, from various fields around the world. These correlate with the GOR trends. The thin lines are approximate hydrostatic gradients for reference only (they should not be taken literally to imply that the reservoirs are necessarily saturated at the top of the oil columns).

Data from over 100 wells that penetrate the pre-Cretaceous were examined as part of a larger review of overpressures within the deeper section of the Central Graben. For this purpose, only those data measurements that could be quantified as of good quality were included. When comparing pressure data between wells spatially, the relative overpressure (difference between the hydrostatic and aquifer pressure gradients) should always be quoted. The hydrostatic gradient was taken as 0.45 psi/ft from surface as standard and, where necessary, the pressure data were also corrected to remove the elfects of hydrocarbon buoyancy. 

Fig. 4. Whilst the Smerbukk and Smerbukk Ser fields (Fig. la) today have pressures on the oil gradient just above the hydrostatic gradient, pressures in structures in Halten Vest are close to the estimated fracture pressures (from leak-off tests). Most wells in the overpressured region are dry, unless traps are sufficiently deep to avoid the fracture gradient, e.g. Kristin (Figs la 5), and this region coincides roughly with the area where the Spekk Formation is in the very last part of the oil window, or already over-mature.

The transport system of the sieve tubes is also a multiplet of generalized transport units (pTU) with the sieve plate pores as organismal capillaries. Though the sieve tubes are thin as such, the dependence of the hydraulic conductivity, on the fourth power of the radius, makes the distinction between them and the pores essential. The effects of occlusion on gw are difficult to calculate but the general features of the sieve tube system permit one to surmise that it has been made to cope with adverse hydrostatic gradients of variable but often large magnitudes. 

Forces generated by hydrostatic gradients of the choroid plexus and arachnoid granulations are not sufficient to account for the movement of CSF. Fluctuation, a back-and-forth movement of the fluid, contributes to this process. 

The temperature distribution in the liquid and in the vapor just above the liquid surface will now be discussed. There is a tendency for a temperature gradient to exist in a liquid because of the hydrostatic pressure of the liquid itself. In many liquids the thermal conductivity renders the usually small hydrostatic gradient completely negligible. However, the thermal conductivity of liquid He I is so small that accurate temperature measurements require a correction for the hydrostatic pressure. For example, at 3 K the temperature gradient induced by hydrostatic pressure is 0.35 mdeg/cm, which is quite significant. 

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