A geo-cellular model of a multiphase hydrocarbon field incorporating fault-seal analysis : Bredasdorp Basin, South Africa
Master Thesis
2015
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University of Cape Town
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Geological 3D static modelling has become an integral tool during the appraisal and developmental stages of a hydrocarbon field lifecycle. The 3D model becomes the basis upon which reservoir heterogeneity and characterisation are understood, hydrocarbon volumetrics are calculated and field development plans are designed. Reservoir compartmentalisation and fault-seal analysis is also an industry topic which has drawn much interest. Having a 3D model allows for fault-seal analyses to be carried out and evaluated using the statistically distributed reservoir properties. This study incorporates the building of a 3D geo-cellular reservoir model with a fault seal analysis of the E-S field, which is located on the north flank of the Bredasdorp Basin. The reservoir model was built using geostatistical methods to populate the several reservoir parameters into the model to calculate a hydrocarbon volume. In addition, a fault-seal analysis was carried out in order to investigate the phenomenon of having an oil accumulation separated from a gas accumulation either side of a fault. The facies modelling was carried out using the object modelling technique, in order to produce a model which is geologically plausible. Most of the remaining reservoir parameters were modelled using a variogram except in the case of water saturation, which was modelled using a J function equation. The volumetrics were assigned per fault block. Using a recovery factor of 75% for gas and 11% for oil, the calculated total recoverable hydrocarbons were 12.6 Bscf and 1.3 MMbbl respectively. The fault-seal analysis showed that the faults separating two of the fault blocks are not completely sealing. All the calculated fault properties supported this view, with the Shale Gouge Ratio (SGR) and threshold pressure relationship indicating a high likelihood for leakage across parts the faults. Pressure data from Repeat Formation Tests (RFT) however, indicates that the hydrocarbon accumulations in both blocks are isolated from each other. This contradiction has informed the recommendation to drill a highly deviated or short horizontal well which will cross the fault and intersect both blocks, and to complete the well using a sliding sleeve, thus providing the flexibility needed in order to manage multi-phase flow.
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El Saadi, O. 2015. A geo-cellular model of a multiphase hydrocarbon field incorporating fault-seal analysis : Bredasdorp Basin, South Africa. University of Cape Town.