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Lookup NU author(s): Professor Andrew Aplin,
Professor Stephen Larter
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We present a method to determine the composition and PVT properties of petroleum in individual petroleum fluid inclusions. Confocal Laser Scanning Microscopy is used to generate three dimensional images of single petroleum inclusions. Because liquid petroleum fluoresces under the laser. the images readily distinguish the liquid and vapour within the inclusion and can be used to determine the inclusion's volumetric liquid:vapour ratio. Using PVT modelling software, the liquid:vapour ratio is used along with the homogenisation temperature to determine the bulk composition. phase envelope, isochore and a range of physical properties of the included petroleum. This is done using an iterative series of PVT calculations which match two parameters: (1) the molar volume of the petroleum at room and homogenisation temperatures; (2) the liquid:vapour ratio of the inclusion at room temperature. Key uncertainties in the method are explored, including the accuracy with which the liquid:vapour ratio can be determined: the composition of the titrant gas used in the iterative procedure; and the composition of the petroleum chosen to model the physical properties of the included petroleum. Data from coeval inclusions suggest that the saturation pressure, Gas-Oil Ratio, viscosity, molar volume, density and surface tension of included petroleum are determined with a precision of a few percent. Confirmation of the accuracy of the method awaits tests using inclusions grown in the laboratory under carefully controlled PVTX conditions. However, it is likely that the physical properties of included petroleums are more accurately modelled by fluids which are genetically related to them. If proven to be accurate, the method will provide a routine method for determining palaeopressure in petroleum systems. Finally, we present data from a Central North Sea example which are geologically realistic and which for the first time record the evolution of fluid pressure and petroleum composition in a petroleum reservoir. (C) 1999 Elsevier Science Ltd. All rights reserved.
Author(s): Aplin AC, Macleod G, Larter SR, Pedersen KS, Sorensen H, Booth T
Publication type: Article
Publication status: Published
Journal: Marine and Petroleum Geology
Print publication date: 28/05/1999
ISSN (print): 0264-8172
ISSN (electronic): 1873-4073
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