Many fields demonstrate significant vertical changes in the oil properties. It is a challenge to explain and simulate these changes which occur under the gravitational forces or the effect of thermal diffusion if the reservoir is thin (up to 40 m) and the temperature gradient is close to zero, which is typical of some fields in East Siberia. Here, other processes have a significant impact on the properties of oil: oxidation, biodegradation, the effect of bottom water near the oil-water contact, etc. At the same time, ignoring the differentiation of oil properties in a flow simulation model (setting averaged properties for the entire reservoir) leads to an incorrect assessment of fluid mobility and to inaccurate estimates of hydrocarbon production volumes.
The paper presents an approach to creating a PVT-model for systems with vertical differentiation of oil properties in the context of one of the reservoirs of the Srednebotuobinskoye field. The analysis of field geological information allows the authors to identify a layer of heavy viscous oil near the water oil contact. Previously the samples with high viscosity values had been ignored as non- representative. Matching the common equation of state to the results of some samples which were taken both near the gas oil contact and water oil contact helps to take fluid properties differentiation by depth into account– fully saturated oil at the gas oil contact and increasing the oil viscosity in the vicinity of the water oil contact. As a result the compositional dynamic model allows to determine oil properties correctly in a reservoir when estimating hydrocarbon reserves, improve history matching process and provide a more accurate predicted HC production.
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