Abstract
Carbonate reservoirs are known as heterogeneous reservoirs due to their pore complexity caused by depositional setting and diagenetic process. This complexity can create comprehension about storage capacity and flow capacity, including water saturation. A reservoir characterisation method using a flow zone indicator (FZI) can be useful to divide reservoir rock based on its flow unit, as well as irreducible water saturation. Reservoir characterisation is applied to the Kujung formation, in Jago and the Bravo Structure, North East Java Basin which has an invalid calculation of Archie's water saturation. First, the flow unit is identified by FZI, then the water saturation of the reservoir is calculated by the Leverett J-Function method for which every flow unit has its irreducible water saturation. From the FZI method, the Kujung formation can be divided into three flow units with their own characteristics. Flow unit 1 has a channelling pore type and a 0.25 Swirr value, flow unit 2 has a vuggy pore type and a 0.39 Swirr value, while flow unit 3 has a highly cemented interparticle pore type and a 0.43 Swirr value. Water saturation, calculated by using the Leverett J-Function method, provides a more precise result compared to Archie's water saturation method, which has been validated by fractional flow test in the Kujung reservoir interval. It is inferred that the reservoir characterisation implies an excellent prediction of water saturation by using the J-Function method.