Summary

Estimating water saturation is one of the main challenging aspects in reservoir characterisation. Good estimation of this parameter enables us to calculate reserve accurately. Hence, it is of great importance to estimate precisely water saturation based on hydraulic flow units of reservoir rocks. In this paper, a modified J-function was used and developed to determine the water saturation in the hydrocarbon reservoirs located in field A, Cuu Long basin. The capillary pressure data (Pc) and water saturation (Sw) as well as routine core sample analysis including porosity (φ) and permeability (K) were used to develop the J-function. First, the normalised porosity (Фz), the rock quality index (RQI), and the flow zone indicator (FZI) factors were used to classify all data into discrete hydraulic flow units (HU) containing unique pore geometry and bedding characteristics. Subsequently, the modified J-function was used to normalise all capillary pressure curves corresponding to each of predetermined HUs. The results showed that the reservoir rock was classified into several separate rock types with definite HUs and reservoir pore geometry. Eventually, the water saturation was determined using a developed equation corresponding to each HU gained by normalised J-function. The equation is a function of rock characteristics including Фz, FZI, lithology (J’), and pore size distribution index (∂). The proposed technique can be applied to any reservoir to determine the water saturation in the reservoir, specially the ones with high range of heterogeneity in the reservoir rock properties.

Key words: Water saturation, rock quality index (RQI), hydraulic unit (HU), flow zone index (FZI), Cuu Long basin.
 

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