Hydrocarbon column

Fluid samples will be taken using downhole sample bombs or the MDT tool in selected development wells to confirm the PVT properties assumed in the development plan, and to check for areal and vertical variations in the reservoir. In long hydrocarbon columns (say 1000 ft) it is common to observe vertical variation of fluid properties due to gravity segregation. 

In Table I are listed the radical products (R )(column 2), AE(x) values (column 3), EA values (column 4) and the experimental temperatures for the one- and ten hour half life rates for the decomposition of trona-symmetric bisalkyl diazenes (columns 5 and 6), (rona-phenyl,alkyl diazenes (columns 7 and 8), peresters (columns 9 and 10) and hydrocarbons (columns 11 and 12). 

Figure 3.13 n-Electron selectivity of different octadecyl-bonded silica gels towards the retention of polycyclic aromatic hydrocarbons. Columns. , LOC-ODS-E, O, LOC-ODS-NE O, HIC-ODS-E, A, HIC-ODS-NE, eluent, 80% aqueous acetonitrile at 30°C. Compounds polycyclic aromatic hydrocarbons 1, benzene, 2, naphthalene 3, pyrene 4, 3,4-benzopyrene. 

Fig. 4.4 Analysis of polyaromatic hydrocarbons. Column two 100x4.6mm id in series, Ci8 bonded-phase packing 3 pm particles. Mobile phase acetonitrile-water, linear gradient from 65 to 90% in 20min, at 1.8mL min-1 inlet pressure 4500psig (31.0mPa) initial, 2700psig (18.6MPa) final ambient temperature UV detector at 254nm. Peaks 1, naphthalene 2, fluorene 3, acenaphthalene 4, phenanthrene 5,...

The inside-out methods (Sec. 4.2,10) can be used for most columns. The Russell method is simple to implement and does work well for a wide variety of refinery and hydrocarbon columns. The Boston method also works well for a wide range of columns and has been shown to work for superfractionators or tall, high-purity columns. Since the outer loops of the two methods are similar, they can be combined with a choice between the two methods, depending on the type of column, as part of the inside loop. 

FIGURE 4-4. Two approaches to the separation of polynuclear aromatics, (a) Reverse-phase separation of isomeric 4-ring polynuclear aromatics using a gradient of 70/30 (v/v) to 100/0 (v/v) acetonitrile/water as shown beneath the chromatogram. Column C,g detection at 254 nm. (b) Normal-phase separation of aromatic hydrocarbons. Column /uPorasil (silica, 10 /urn) 3.9 mm ID x 30 cm (2 columns) mobile phase hexane flow rate 8 mL/min. (Fig. 4-4b reproduced from reference 1 with permission.)... 

Continued supply of hydrocarbons from the source rock increases the vertical height of the hydrocarbon column (Zo). As soon as Zq is large enough, i e as soon as the buoyancy force of the hydrocarbon column is greater than the resistant force of the carrier rock, vertical upward migration through the carrier rock will start. 

Hydrocarbons accumulated along an inclined barrier rock - carrier rock interface, will start to migrate laterally updip through the carrier rock when the critical height of the hydrocarbon column is exceeded again by addition of hydrocarbons. 

The magnitude of the resistant force to hydrocarbon movement caused by capillarity is not influenced by the groundwater flow condition and is also given by Equation 4.15. The net driving force for a vertical height Zq of a hydrocarbon column influenced by vertically upward or downward directed groundwater flow can be derived from Equations 4.5 and 4.6 and equals... 

The critical height of the hydrocarbon column under vertical groimdwater flow conditions becomes... 

From expression 4.22 follows that vertically upward directed groundwater flow will diminish the critical height z of the hydrocarbon column while vertically downward directed flow will increase its vertical height. 

The maximum height of a hydrocarbon column that can be contained in a hydrostatic trap is determined by the sealing capacity and geometry of the rocks, or rocks and faults that form the trap. When the vertical distance from crest to spill plane of the trap (Figure 5.1) is less than the maximum height of the hydrocarbon colunm Zj (Equation 4.17), the accumulating hydrocarbons may fill the trap to its spillpoint. As hydrocarbons continue to migrate into the... 

Under the assumption that the capillary pressure gradient across the carrier rock-barrier rock interface is the only significant resistant force affecting hydrocarbon accumulation in a conventional hydrostatic trap, i.e. the influence of the hydrodynamic condition in the barrier rock on its sealing capacity can be considered to be negligible, the maximum height of the hydrocarbon column below the barrier rock can be given by Equation 4.22... 

Figure 8.2 Calculated hydrocarbon column heights below hypothetical cap rock structure at different times before present (from Lehner et al., 1987. Reprinted by permission of Editions Technip).

Watts, N.L., 1987. Theoretical aspects of cap-rock and fault seals for single- and two-phase hydrocarbon columns. Marine and Petroleum Geology, Vol. 4, November 1987, pp. 274-307 Weber, K.J., 1982. Influence of common sedimentary structures on fluid flow in reservoir models. Journal of Petroleum Technology, March 1982, pp. 665-672 Weber, K.J., 1987. Hydrocarbon distribution patterns in Nigerian growth fault structures controlled by structural style and stratigraphy. Journal of Petroleum Science and Engineering, 1, pp. 91-104... 

CONTROLLED BY EXCESS HYDRODYNAMIC HEAD ABOVE ACCUMULATION. HYDROCARBON COLUMN REACHES EQUILIBRIUM LENGTH WHEN UPWARD/ DOWNWARD FLOW FORCES EQUAL... 

Watts, N.L. 1987. Theoretical aspects of cap-rock and fault seals for single- and two-pha.se hydrocarbon columns. Mar. Pet. Geol., 4 274-307. 

Zieglar, D.L. 1992. Hydrocarbon columns, buoyancy pressures, and seal efficiency comparisons of oil and gas accumulations in California and the Rocky Mountains area. Am. Assoc. Pet. Geol. Bull., 76 501-508. 

Coarser lithologies, such as siltstones, have lower retention capacities due to their larger pore throat sizes (Watts, 1987). The retainable hydrocarbon column lengths are therefore strongly controlled by... 

Simple one-dimensional reservoir models (two phase Darcy flow) indicate that, in general, the flow rates across permeable fault seds will be too high to sustain high pressure gradients or corresponding differences in hydrocarbon column lengths over geo-... 

Gibson (1994) presents observations from the Tertiary sand-shale sequence of the Columbus Basin, offshore Trinidad. From an analysis of fault-sealed hydrocarbon columns, he concludes that the more significant seals are developed where the ratio of fault throw to shale layer thickness is less than 4 (i.e., the shale bed is >25% of the displaced section). 

Fig. 11. Graph illustrating the pore-pressure profile through the Brent Group on each side of Fault 1. FW, footwall HW, hangingwall. Note the upwards increase in pressure difference through the hydrocarbon columns. The two aquifer gradients are believed to be coincident (within the uncertainty of the tool measurements) since the reservoir is continuous around the southern end of the fault (see Fig. 3).

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