ABSTRACT:

A detailed description of geological heterogeneities, a good transfer to the dynamical model and the identification of the most important factors in dynamic simulation are the key-points for a reliable modelling of the reservoir behaviour. El Borma is a giant oil field in a mature stage of production through secondary recovery by water injection. About 190 wells (some of them horizontal) have been drilled; an infilling well campaign aiming at increasing the recovery and an EOR WAG pilot project have been recently started. The field is producing from 4 main reservoir levels composed of fluviatile sediments characterised by strong facies heterogeneities and crossed by some sub-seismic faults. The geological study was carried out using:

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    a cluster analysis process on logs

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    non stationary facies simulations

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    petrophysical simulations

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    a strong integration between geological data and a rich production history

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    an upscaling method based on VPC and Laplace algorithm

Dynamic modelling after the ranking of upscaled geostatistical images confirmed the good reservoir description with good matches since the first runs. After the fine tuning phase the static model was substantially unchanged. Moreover, good results in the final match were also determined by the identification and simulation of some phenomena like gas relative permeability hysteresis and water injection characterisation. Gas relative permeability hysteresis enabled us to match the strong reservoir depletion in the first phase of field production and, at the same time, assured a GOR control after water injection activation. In a mature field with high water-cut (85-98%), little and generally acceptable differences in water-cut match have a dramatic influence on pressure evolution. Therefore, a detailed description of water characteristics (injection vs formation water) is mandatory.

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