9In an oil reservoir, the geometry of the interface between water and oil is critical in determining the volume of oil trapped below the top seal. If the interface is planar and hori-zontal, the volume calculation is fairly simple, but if the interface is tilted or undulating, estimation of the volu...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.580.150 http://www.geus.dk/publications/bull/nr4/nr4_p09-12.pdf |
| Summary: | 9In an oil reservoir, the geometry of the interface between water and oil is critical in determining the volume of oil trapped below the top seal. If the interface is planar and hori-zontal, the volume calculation is fairly simple, but if the interface is tilted or undulating, estimation of the volume of the trapped oil is complex as it depends on the combined structural and fluid contact geometry. Since accumulation of the oil may take place over a time span of several million years, while the reservoir is experiencing burial and com-paction, the charge history must be studied using dynamic methods that account for these changes and for flow in both the oil and water phases. These processes have been studied quantitatively at the Geological Survey of Denmark and Greenland (GEUS) in a project that has combined the burial model with a fluid flow simulator. The modelling study shows that filling of a chalk reservoir can have a very long and com-plex history dominated by very low fluid flow rates (cm/year). The resulting modelled present-day situation exhibits a very irregular oil distribution and a non-planar geometry of the fluid contacts, and shows marked similarities to that shown by the field data. Oil–water contact and free water level The positions of the oil–water contact (OWC), the gas–oil contact (GOC) and the associated free water level (FWL) in an oil- and gas-field are some of the most important factors in estimating the in-place hydrocarbon volumes of a given field. Thus it is important to be able to analyse and predict tilted or irregular fluid contacts (Dennis et al. 2000; Moss et al. 2003; Dennis et al. in press; Vejbæk et al. in press). The fluid contact can be defined in two radically different ways: The OWC is defined by setting a threshold for the oil saturation, whereas the FWL is defined where the pressures The history of hydrocarbon filling of Danish chalk fields |
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