Publications

Walio field in Salawati basin, onshore West Papua, mainly producing from Miocene-Kais reefal limestone, is the largest oil field in PetroGas (Basin) Ltd concession and it has been producing since 1975 from more than 300 wells. After oil production peak at 57,800 BOPD in 1977-1978, the production continuously declined due to great escalation of water cut following ESP implementation. It has become a practice that perforation(s) were mostly placed within the good intervals rather than the poor ones to gain maximum withdrawal. This fact indicates that there must be some parts of the reservoir intervals which might be still retaining some recoverable reserves to be extracted. A set of reservoir-technical evaluation is applied to spot the remaining recoverable reserves. Strong aquifer support that keeps the reservoir pressure above the saturation pressure all the time, has contributed to relatively high reservoir recovery factor (RF) which is about 44% to date. During production life of the field, aquifer will move preferentially towards the more porous and waterwet zone whereabouts the oil displacement takes place that subsequently improved the recovery factor. Other prominent controlling factors of field RF in carbonates are wettability, reservoir connectivity and mobility ratio. The latter two mentioned factors are related each other due to reservoir carbonate heterogeneity. As supporting evidence, cased-hole logging performed in some wells attested higher oil saturation mostly within poor reservoir section albeit the degree of geological connectivity in the field is still to be uncertain. In situation of almost all good intervals have been exploited, unlocking the un-swept oil from the poor zones become more attractive to maximize oil production during primary depletion stage. A combination of geological model, cased-hole logging campaign and well review activities are integrated to realize new perforation opportunities from the poor zones with successful results.