Publications

The LRLC reservoir is one of the proven and productive zones in the Offshore North West Java Area. The reservoir is a member of the Upper Cibulakan formation and it is widely distributed in this large area. The reservoir mainly consists of shaley sand facies with occasionally thin limestone stringers deposited in the shallow marine environment, from neritic to littoral. The LRLC reservoir is characterized by relatively low gamma ray (10-30 degs API) and low resistivity value (1-2 ohm) which makes it difficult to distinguish it from a water-bearing formation. Using conventional log analysis, the low resistivity and high shaliness will yield high water saturation. This situation will lead into the pessimistic reserve calculation. The high-water saturation in the reservoir may produce hydrocarbons. The challenge for the subsurface team is to find a proper methodology to evaluate such a reservoir to provide a more realistic evaluation in terms of reserves calculation and also to find the optimum perforation interval. This paper contains a proposed methodology including utilization of Buckle Plot and Apparent Water Resistivity (Rwa). Buckle plot has been introduced since 1965 (Buckle, 1965:42-52) and principally is a number obtained from the result of multiplication between water saturation and porosity which is Bulk Volume Water (BVW). The BVW can be utilized to observe whether the zone is in the irreducible or transition zone by assuming the same grain size. The different grain size will show a different value of BVW. On the other hand, Rwa technique is used to recognize hydrocarbon bearing zone which higher from lowest Archie’s derived Rwa. The value and trend of total gas (TG) from mud logging data is very crucial data that needs to be integrated to obtain a more comprehensive analysis. This paper employs two methods of reconstruction of BVW plot and Rwa log to determine by-passed hydrocarbon potential in the LRLC reservoir in the ONWJ Area.