Hydrocarbons pore water

The pores between the rock components, e.g. the sand grains in a sandstone reservoir, will initially be filled with the pore water. The migrating hydrocarbons will displace the water and thus gradually fill the reservoir. For a reservoir to be effective, the pores need to be in communication to allow migration, and also need to allow flow towards the borehole once a well is drilled into the structure. The pore space is referred to as porosity in oil field terms. Permeability measures the ability of a rock to allow fluid flow through its pore system. A reservoir rock which has some porosity but too low a permeability to allow fluid flow is termed tight . 

Poorly sorted sediments comprise very different particle sizes, resulting in a dense rock fabric wifh low porosify. As a resulf the connate water saturation is high, leaving little space for the storage of hydrocarbons. Conversely, a very well sorted sediment will have a large volume of space between the evenly sized components, a lower connate water saturation and hence a larger capacity to store hydrocarbons. Connate water is the water which remains in the pore space after the entry of hydrocarbons. 

A reservoir is not a subterranean lake of pure oil or a cavity filled with gas. It is a porous and possibly fractured rock matrix whose pores contain oil, gas, and some water, or else, more rarely, it is a highly fractured rock, whose fractures contain the fluids. Such a resewoir is usually located in sandstone or carbonate rock. The rock matrix of an exploitable reservoir must be porous or fractured sufficiently to provide room for the hydrocarbons and water, and the pores and fractures must be connected to permit fluids to flow... 

Eadie, B.J., Landrum, P.F., Faust, W. (1982) Polycyclic aromatic hydrocarbons in sediments, pore water and the amphipodPontoporeia hoyi from Lake Michigan. Chemosphere 11(9), 847-858. 

Kosian, P.A., E.A. Makynen, P.D. Monson, D.R. Mount, A. Spacie, O.G. Mekenyan, and G.T. Ankley. 1998. Application of toxicity-based fractionation techniques and structure-activity relationship models for the identification of phototoxic polycyclic aromatic hydrocarbons in sediment pore water. Environ. Toxicol. Chem. 17 1021-1033. 

Free-phase NAPL refers to NAPL that exists as an independent phase, not as a dissolved component in the pore water or pore atmosphere. The environmental concerns associated with sites affected with free-phase NAPLs revolve around hydrocarbon-impacted soil (residual hydrocarbon), the NAPL itself (which can serve as a continued source for groundwater contamination), dissolved hydrocarbon constituents in groundwater, and hydrocarbon vapors. The detection of free-phase NAPLs in the subsurface presents many challenges. Two questions frequently arise at sites impacted by NAPLs how much is there and how long will it take to clean up. Before one can address these two questions, assessments of the type and subsurface distri-... 

Graphs of relative permeability are generally similar in pattern to that shown in Figure 5.10. As shown, some residual water remains in the pore spaces, but water does not begin to flow until its water saturation reaches 20% or greater. Water at the low saturation is interstitial or pore water, which preferentially wets the material and fills the finer pores. As water saturation increases from 5 to 20%, hydrocarbon saturation decreases from 95 to 80% where, to this point, the formation permits only hydrocarbon to flow, not water. Where the curves cross (at a saturation... 

Socha, S.B. and Carpenter, R. Factors affecting the pore water hydrocarbon concentrations in Puget Sound sediments, Geochim. Cosmochim. Acta, 51(5) 1273-1284,1987. 

Mitra, S. and R.M. Dickhut. 1999. Three-phase modelling of polycyclic aromatic hydrocarbon association with pore-water-dissolved organic carbon. Environ. Toxicol. Chem. 18 1144—1148. 

The gas is stored not only in the pore volume. Much of the gas will dissolve in the formation fluids, both hydrocarbon and water. Some of the C02 and H2S will react with components in the reservoir and form new minerals - the so-called mineralization. 

As discussed in previous sections, there are numerous factors that can modify the toxicity of materials. The prediction of the toxicity of mixtures is also difficult. One of the best attempts at toxicity prediction has been formulated by Swartz et al. (1995) and predicts the sediment toxicity of polynuclear aromatic hydrocarbons. The model is based on the concentration of 13 PAHs in collected sediments, the predicted concentration in the sediment pore water, and the toxicity of these concentrations as determined by a large toxicity data set. 

Finally, carbonate cements reveal the sources of dissolved carbon in the evolving pore waters of the San Joaquin basin. The clastic-rich basin is free of carbonate rocks but contains a considerable amount of organic matter, both in fine-grained sediment and as relatively recent hydrocarbon accumulations. Potential carbon sources for the carbonate cements are marine shell tests, thermogenesis and, possibly, organic reactions related to the presence of the oil. 

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